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# Copy Command In Cmd

You can copy an ASCII text file that uses an end-of-file character (that is, CTRL+Z) to indicate the end of the file. Type in cmd and press ENTER; Right Click anywhere in window (see image below). The first does the same as dragging a file to a new location on the same hard disk; the second. exe will exit, no search window is shown. If you use only FAT drives, VSS will not function. When I execute the command copy /y ". I need to copy a folder from my usb harddrive to the program files folder on the c drive. copy running-config. The Linux Command Line A Book By William Shotts. , a library or school computer), or an otherwise non-administrator account. le druide sans la potion. The first is to open the command-line window with Ctrl-f, then use normal-mode commands to paste. This publication provides IBM® Copy Services Manager CLI commands that you can enter to manage data-copy functions. This also works for files in the Finder. exe will also work. This program should copy the files from the source fold. I need to put these into a. Select Mark from the menu Click and drag over the text you wish to copy. The Server command-line arguments can be found under Command-line arguments (Server). Right click anywhere on the command window. destination is the new place – file or directory – where you want to copy it to. Keep in mind that if you're on a shared computer (e. Any ideas would be greatly appreciated. You can copy an ASCII text file that uses an end-of-file character (that is, CTRL+Z) to indicate the end of the file. The xcopy command does not have this requirement. There are some CMD commands that are so useful and easy to use that even regular users see the Windows command prompt as a key part of the operating system. Instead I get the two files concatenated, (including the trailing CR/LF's as I would expect ), but also one additional character, the hex character for a right-arrow symbol - 0x1A. Enter the "copy" command. exe: ora_br_copy. cp is the command entered in a Unix and Linux shell to copy a file from one place to another, possibly on a different filesystem. pdf && copyq select 0 Check their wiki for more documentation and usage examples. Then press ctrl c (which is copy) , which will copy the full text into memory. source is the source file or directory you want to copy. If you don't specify any arguments, MOVE will display its command dialog. Command prompt's ability in recovering deleted files is restricted to a large extent, which means that you may not be able to fully restore every lost file by using CMD. It has been available as part of the Windows Resource Kit and was first introduced as a standard feature in Windows Vista and Windows Server 2008. Is there a way to do something like: cp mystuff. Most commands affect the document's selection (bold, italics, etc. Are you a Windows OS user? Read these posts:. As you know from using. You can also use quotes in the command line and use the complete folder names. The directories are stored sequentially in a virtual stack. You can use it in your case as follows: tee ~/folder1/test. scp stands for secure copy, it is command-line utility that allows users to copy files and directories securely between two and more systems. Read below about, 'how to enable copying and pasting texts in Windows Command prompt'. You can copy and command and paste it directly into your Command Prompt. txt < ~/test. mv command is the basic command in Linux. The script is kept inside a batch file, with the extension. mv command syntax. Using Clip. Batch File can copy files in computer easily. In prior versions of Windows, you'd have to select your text, click on the C:\ icon for the drop-down menu, choose the Edit command. In the past left click was copy and right click paste (only CMD not powershell) CTRL+V is a pretty new way of pasting I think. The copy-paste feature has also been enhanced in Windows 10. all All of the above. 0 and above. Option 3: Manually copy the file to the Opengear device then run netflash using the local file To begin, login to the Opengear CLI as root, or an admin group user and become root with: sudo -s. pauses the execution of a batch file and shows a message. Cara Copy File Menggunakan CMD ( Command Prompt ) - Windows Command Prompt atau biasa disebut DOS Prompt adalah jendela unuk menjalankan perintah-perintah atau mengeksekusi file dengan cara menuliskan perintahnya diikuti dengan menekan tombol Enter yg merupakan standar operasi dari MS-DOS sebelum era Windows. You can use this command to duplicate objects in drawing. Re: Copy Paste from Excel Cells into Command Line You have to make sure the command line is active, or it will paste into the drawing area as an ole object. The copy shell command does support wild cards. Regardless of the method used to copy files, you aren't going to suddenly decrease the time it takes by using one method over another. 3 for a description of these options. start command prompt. Once the properties of the command prompt open up, check QuickEdit Mode,Insert Mode and Enable Ctrl key shortcuts and click on OK button. cp and rsync are one of the most popular commands for copying. If you need to just upload one file you can stop reading after the first option since it covers probably most of needs to upload a single file. org! jq is like sed for JSON data - you can use it to slice and filter and map and transform structured data with the same ease that sed , awk, grep and friends let you play with text. In this case, /b applies to the file preceding /b. Odd copy command. Use xcopy unless you need a complete disk image copy. It seems that we chug along with the same commands over and over in our daily lives as network admins. exe on Windows or bash on Linux and OS X. mpg and I want to copy this file to /home/levan/kdenlive. But typing in everything to Google’s search bar doesn’t sound too appealing to me. It is extremely easy to create shortcut to a file or folder using the Shortcut Create wizard in Windows, but there's no direct way to create a shortcut from the command line. How to copy a file to multiple folders using the Learn more about copy a file to multiple folders. Amazon S3 is a reasonably priced data storage service. Command Line How to manage wireless networks using Command Prompt in Windows 10 When you need to manage your wireless network connections, using the Settings app or Control Panel may not be enough. Accessing network file shares from a command prompt March 8th, 2007 If you’ve ever tried to access a network file share in a command prompt by simply using the cd command, you’ll know that it just complains that “CMD does not support UNC paths as current directories”. on the windows command line, run this command (e. It can record a bag, republish the messages from one or more bags, summarize the contents of a bag, check a bag's message definitions, filter a bag's messages based on a Python expression, compress and decompress a bag and rebuild a bag's index. Yes, you can do it. Re: Command Prompt (CMD) - Copy/Paste - Windows 10 The screenshot in the tutorial contains a cmd. Permissions aren't automatically inclusive, you will need to give both 'essentials. Option 3: Manually copy the file to the Opengear device then run netflash using the local file To begin, login to the Opengear CLI as root, or an admin group user and become root with: sudo -s. Press again to exit full. Paste it using the shortcut Ctrl + V. A situation may arise when you want to execute a (shell) command from the C# application. Normally, we right-click on text to perform these task but in case of command prompt, these features are hidden. Most commands affect the document's selection (bold, italics, etc. Any text selected in the browser when one of these commands is executed will be cut or copied to the user's clipboard. Using copy command, we can copy files from one directory to another directory. txt to D:\Temp\Test Folder1. This command is similar to the Linux cp command, but it does not match with the full functionality of cp. The default syntax for cp is >cp source destination. ASMCMD is a command-line utility that you can use to view and manipulate files and directories within ASM disk groups. To copy, click and drag with your left-mouse button to select text in a Command Prompt Window, then right-click To paste, either at the command prompt or in a text file, right-click. png && copyq select 0 To copy a data file (you need to indicate the MIME type): copyq write application/pdf - < file. Doing so will open the Command Prompt program. Here is the list of all Windows CMD commands sorted alphabetically along with exclusive CMD commands pdf file for future reference for both pro and newbies. By default, you are prompted when you replace this setting, unless the copy command is executed in a batch script. Running Previous Commands Again Searching through the history is great and all, but I’d rather not have to copy and paste found commands. It would be perfect if we could implement the procedure at the URL below on the command line. Paste it using the shortcut Ctrl + V. This switch copies hidden and system files in MS-DOS mode. For the command for copying with the clipboard, see Cut, copy, and paste. CMD is a command line interpreter – a program designed to understand the commands input by a user, from a text file, or any other medium – in Windows NT family. The first does the same as dragging a file to a new location on the same hard disk; the second. exe) allows copy and paste function, it is not user-friendly, be it in Windows 7, Windows Vista, Windows XP, etc. To launch Command Prompt select Start -> Run and type cmd in the box. To turn on Quick Edit mode, follow these steps: Right-click on the title bar of Command Prompt and select Properties. IN (set) used to provide list for looping. You will see Welcome to the Microsoft telnet client displayed on the command prompt. Instead of typing the commands on psql every time, you could have a. mv command options. What we have found is that the majority of incidents occur with copy and past and move related commands. This means that the window will remain after the command has been run. Run a FreeFileSync batch job. The tail command is probably one of the single most handy tools you have at your disposal for the viewing of log files. Normally, we right-click on text to perform these task but in case of command prompt, these features are hidden. Disclaimer: use these command at own risk. If I am using the terminal in a Gui, there aren't problems because i simply highlight the text and copy it, but how can I copy the text without using the mouse for example from a text only system ? Thanks and sorry for my poor English, Francesco. While the using the Copy as Path command is a handy aid when working in a Command Prompt window, it has other uses too. This reveals or changes the encryption of records and files on NTFS volumes. After you complete the copy, run that same line again. Accessibility Wizard – accwiz 3. -create-file-list-exclude-files. From the command line, you can navigate through files and folders on your computer, just as you would with Windows Explorer on Windows or Finder on Mac OS. You can copy an ASCII text file that uses an end-of-file character (that is, CTRL+Z) to indicate the end of the file. With this easy-to-use and yet professional Word to Text server converter, you can convert Word to Text, command line enabled, in only a few minutes. cp and rsync are one of the most popular commands for copying files and directory. However, AOMEI Backupper offers a partition/drive level copy while xcopy doesn’t. ) Simply open a command prompt. So here I will tell you how to find and use them. The rosbag command-line tool provides functionality for ROS bags. 2,) Turn on "QuickEdit Mode" via: A. display host name. If you look at the command, I use the “start” cmd and then supply (“”) a literal nothing as a switch to the “start” cmd. The above command will print out the contents of dmesg and allow you to scroll through the output just as you did viewing a standard log with the less command. The bcp utility is a command-line tool that uses the Bulk Copy Program (BCP) API to bulk copy data between an instance of SQL Server and a data file. The boldface type below (that follows the command prompt) is what you should type as you work through this tutorial. Powershell is a cross-platform, task-based command-line shell and scripting language that helps rapidly automate tasks that manage operating systems (Linux, macOS and Windows) and processes. (It starts at Z: and moves backward). After you complete the copy, run that same line again. Using the method described by seanyboy here: I'm not sure on how i can write a 'for' loop to go through each 'dest-machine' and perform step 2. xcopy /heckod is what I use. To get this functionality, head to. exe [enter] The copy command may be generalized as follows: [prompt location]\> copy [source item] [target location][\optional rename] [enter] List Directory Contents. The pipe (|) operator reads the output from one command and writes it to the input of another command. cp is shorthand for copy. For the purposes of this guide, we'll be using it to create new disk images (although there is a lot more the command can do). Xcopy is a built in command on Windows OS which has advanced features than the basic Copy command. XCOPY usage and attributes can be obtained by typing "XCOPY /?" in the DOS Command line. Part 2: How to copy and paste in Command Prompt on Windows 10. cp your-file. txt" directly on your clipboard. See also: Add Windows User Command line. So here I will tell you how to find and use them. It may be by the default in Windows 10, if not then what you can do is just follow this. Launching and Managing Command Prompt; Win + R, then type 'cmd' R un Windows Command Promt: Win + X, then C: Start C ommand Prompt via Power User Commands: Win + X, then A: Start Command Prompt as A dministrator via Power User Commands: type 'exit' Exit Command Prompt: Alt + Enter or F11: Switch to full-screen mode. The trick is the double-quotes. Command get can download even folder, not only file. The first is to open the command-line window with Ctrl-f, then use normal-mode commands to paste. Are you a Windows OS user? Read these posts:. Alternatively, you can press F2 to copy a certain number of characters from the previous command to the current one. Step 1: Run CMD with Administrators permission. Go to My Computer > C:\ drive or the drive where you installed your Windows. scr and drag and drop it into your plan view. One common scenario is that you wish to check, and then reduce, the disk space that Volume Shadow copy consumes. PUSHD, and POPD. In this article, we gonna show you an easy way to create The Matrix rain in your Command Prompt. Xcopy is a built in command on Windows OS which has advanced features than the basic Copy command. Command Prompt and CMD Commands are unknown territories for most of the Windows users, they only know it as a black screen for troubleshooting the system with some fancy commands. Double-click Startup On Windows. Let’s assume that the regular file with content is named sourceone. If the screen is getting too full, just type "Cls" and hit enter to clear it. For that, start typing in cmd to the windows search. Discover why the command line is an agile, scalable, and extensible technology. sc start VSS. Accessibility Controls – access. Is it possible to set a Build Step (Command line) to copy database. doc E:\NewDirectory. Just follow these simple steps and then you are good to go. execCommand () method. Using it, you can copy files between systems without logging into them, as if by magic. Once you do that you can paste it into the command line. With this two tools, you can also clone USB drives via command lines. Copy Datastore Folders or Files in the VMware Host Client Please help me ! Thank you. A cmdlet Measure-Command can be used to measure the time it takes to run a command. [tags]scp, windows, secure copy, ftp, putty, scp clients[/tags]. -create-file-list Create a file list of a path. bat " extension i. txt Note that tee also writes the input to the standard output. Method 3: Uninstall Power Copy 1. See the previous section. Learn Enough Command Line to Be Dangerous is available as an ebook, an offline video series, and as a structured, self-paced online course. Any ideas would be greatly appreciated. The CMD commands in Windows are very useful. This tool copies the data redirected or passed to it, into the. Batch File []. This batch command is used for copying files from one location to the other. While the using the Copy as Path command is a handy aid when working in a Command Prompt window, it has other uses too. Yes, you can do it. Type: help copy for the syntax and a list of the available switches. Note: You can't start a service if Startup type is on Disabled. For example, to generate the System information and copy the output directly to the clipboard, type the following: Systeminfo | Clip. 83 bronze badges. Valid values are COPY and REPLACE. So click twice inside the command line (not double click, just twice slowly) the first click only usually makes Autocad the active window again after leaving Excel, and the second click makes the command line active. The above command is one of the most crucial Command Prompt Windows 10 commands. Command Prompt. 3 Plink command line options. It is capable of moving files, directories, and even whole drives from one location to another. The copy command copies larger files in parts til it's completed. I'm trying to figure out a way to copy the current text in a command line to the clipboard WITHOUT touching the mouse. The Linux command line, the Terminal, can be easily accessed through the Application. User should have administrator/read and write permissions on the servers. The course includes full online access to the book content, streaming videos, progress tracking, exercises, and community exercise answers. See the previous section. ), while others insert new elements (adding a link), or affect an entire line (indenting). What makes robocopy different from xcopy and copy? robocopy, it can copy the files metadata. exe will exit, no search window is shown. Wait for the results to show up and then click the command prompt option. exe) It was done on W10 beta. The script is kept inside a batch file, with the extension. The command. Open Command Prompt, and type "title", followed by the text that you want the Title bar to read. It would be perfect if we could implement the procedure at the URL below on the command line. The diskutil command is only for disk management, when it comes to creating and restoring images there are two other commands to know of. Click on OK. ssh-copy-id [email protected] – add your key to host for user to enable a keyed or passwordless login Searching grep pattern files – search for pattern in files grep -r pattern dir – search recursively for pattern in dir command | grep pattern – search for pattern in the output of command locate file – find all instances of file System Info. Normally, we right-click on text to perform these task but in case of command prompt, these features are hidden. The Windows command prompt is a feature that's been a core part of the Windows operating system for a long time. Annoyed with the situation we have gotten drafters to fill out a log that records the time of the crash, how long the crash took (estimates only) and what the last command was that was used. You can open the command line interface by pressing shift + F2. Many people when using Windows only deals with the GUI Windows interface, so they don't have an idea about any cmd commands and even what command prompt is. IE10 and above added support for the 'cut' and 'copy' commands through the Document. The cp command helps you to do so. If you want to copy ostechnix. Thanks! Copy a file from a Windows command line 2012-03-01 13:48. This manual describes GNU make, which was implemented by Richard Stallman and Roland McGrath. In the command prompt window, type robocopy c:\finance\ d:\finance\ /mir /dcopy:t and press Enter, replacing c:\finance\ with the path of the folder you want to copy, and d:\finance\ with the path. For example (I actually used these folder names successfully): copy c:\"program files"\"this is a test folder"\test. If you want to increase the speed of filling folder names in the command line you can simply copy the CommandPromptPortable. It is capable of moving files, directories, and even whole drives from one location to another. A friend of NoW, Glenn Reimche, shared a much better way using copy command line without the IF statement. This tool copies the data redirected or passed to it, into the. That is faster and more powerful, but requires finding out what the commands are. Altera Command-Line Tools for Board Bringup and Diagnostics This section describes Altera command-line tools useful for Nios development board bringup and debugging. It is a symbol or series of characters at the beginning of a line that indicates the system is ready to receive input. For example: $pbcopy < file. The cp command helps you to do so. start command prompt. It permanently moves the files or directories from one location to another and deletes the files in the source. The syntax is:. You can copy and paste with the familiar CTRL + C to copy and CTRL + V to paste keyboard shortcuts. Now again an important option: cp -r. Do not forget to terminate path with slash. The cp command has several command line options that helps to deal with the symbolic links. exe in the search field in the Start menu or click on Start, then Accessories, and then click on the Command Prompt icon. mp4 files together (because VirtualDub would not do it) and I stumbled across a handy command line option. txt delimiter '|'. Now, when you're in the command prompt, you can type Xcopy command as below to copy folders and subfolders including contents. Options exist for many terminal commands. I often need to copy some text line from the command line in an text editor (emacs or nano). Is there a way to do something like: cp mystuff. Segitu kiranya hehe :D Jadi Maksud saya kali ini yaitu hanyak ingin berbagi ilmu yang saya ketahui, yaitu Copy Folder dengan Command Prompt, yah ini mungkin bukan cara seperti biasanya dalam meng-copy suatu folder. Windows users can double-click on the sqlite3. txt file on your system. See the previous section. It typically ends in a$. Run a FreeFileSync batch job. Whenever I want to copy a drive I just select all files in Windows explorer except for the windows swap file and copy them. Hi, I am facing the issue described in the title, some of the command line arguments for JLink commander don't seem to work. I'd like to write a script to backup some files to my iCloud drive. If you look at the command, I use the “start” cmd and then supply (“”) a literal nothing as a switch to the “start” cmd. Enabling Copy & Paste In Command Prompt So, we have made this article that will help you to learn the process of enabling copy and paste in command prompt with simple steps. Save your file with a ”. A command line scp client for windows. This manual describes GNU make, which was implemented by Richard Stallman and Roland McGrath. The first, hdiutil, is used to manipulate disk images. mv command syntax. This tutorial shows how to copy text from Command Prompt to Window 7 Clipboard and then paste it into a Notepad. mp4 files together (because VirtualDub would not do it) and I stumbled across a handy command line option. Go to start , in the search bar type cmd , and right click the cmd file. asked Jun 11 '10 at 11:03. The simplest use of the cp command is to copy a single source file to a target directory. Possible reasons for VSS failures: For VSS to work, at least one volume in your computer must be NTFS. Open Settings in Command Prompt. Use cp followed by the file you want to copy and the destination where you want it moved. Windows Mac OS X Linux. You can also choose a type of file for example: manual*. There are two modes of Windows Disc Image Burner, visual mode and command line mode. It is normal practice to open the Windows command prompt and execute commands. In this tutorial we'll show you how to copy and paste in Command Prompt on Windows 10 / 8 / 7. exe con (using the type command) c:\> type files\docs\atari. cp is the command entered in a Unix and Linux shell to copy a file from one place to another, possibly on a different filesystem. First you have to run the DOS program with elevated permission, that is as an administrator. First, move the folder that you want to replicate the structure of, to a new folder that has nothing else in it. Instead, use the REPLACE console command. 1) Command Line - GUI tool see below Use RoboCopy (Robust File Copy) a command-line file copying tool built into Windows. With this two tools, you can also clone USB drives via command lines. Displays help at the command prompt. createpoint test2. Now you can select texts in the command prompt using the mouse or keyboard, copy, and paste it into other programs. However, AOMEI Backupper offers a partition/drive level copy while xcopy doesn’t. Although the "Command Prompt here" shell extension often seems to make a short cut to a command prompt redundant, it can be quite useful to have one or even several at hand, especially since a shortcut can open a customized command prompt. By typing commands at the command prompt, you can perform any tasks on your computer without using the Windows graphical interface. The nice thing is that this utility is most often made available from boot command prompts when you are running from a command prompt provided by a utility like PE tool provided in Windows Automated. Segitu kiranya hehe :D Jadi Maksud saya kali ini yaitu hanyak ingin berbagi ilmu yang saya ketahui, yaitu Copy Folder dengan Command Prompt, yah ini mungkin bukan cara seperti biasanya dalam meng-copy suatu folder. See also:. The boldface type below (that follows the command prompt) is what you should type as you work through this tutorial. MS-DOS commands make little difference between a file and a directory. 1 Overview of make. org is a web site devoted to helping users of legacy operating systems discover the power of Linux. exe or simply cmd) is a command shell based on the MS-DOS operating system from the 1980s that enables a user to interact directly with the operating system. It would be better if it would accept the "Enter" (CRLF) from a copy/paste list of entries like. I have a program where you can choose a source folder and a destiantion folder. This page describes the commonly used options and how to use them. 1) • AWS Command Line Interface on GitHub (p. sort the screen output. Enter number of cycles to retain the data. rtf TestFile-copy. mv Here, the file in the source path is removed, after copying to destination path. This also works for files in the Finder. Here's a primer on how it works, and how you can do almost anything with it. 52, provided for free under the Info-ZIP license. Computerhope. If this parameter is not specified, COPY will be used. All you now have to do is run the copy command located at the top of this post. When we log onto the computer the shell will automatically start. Type in cmd and press ENTER; Right Click anywhere in window (see image below). execCommand ( aCommandName, aShowDefaultUI, aValueArgument ). To copy an image (you need to indicate the MIME type): copyq write image/png - < file. LPT1 = "PDFtoPrinter. Is it possible to set a Build Step (Command line) to copy database. ws-commands. cp and rsync are one of the most popular commands for copying files and directory. A situation may arise when you want to execute a (shell) command from the C# application. As you know from using. Copy command Optional study: copying folders. I have a program where you can choose a source folder and a destiantion folder. copy running-config tftp [verbose] address {A. Required parameters Object Name-on ObjectName Sets path and/or name of the object to process. The new command line is a nice feature. Are you a Windows OS user? Read these posts:. pdf && copyq select 0 Check their wiki for more documentation and usage examples. This feature is available in all the operating systems,. It will then monitor the terminal for any commands. org but in much greater detail. The pipe (|) operator reads the output from one command and writes it to the input of another command. And CMD Commands are the specific set of instructions given to Command Prompt to perform some kind of task or function on your Windows PC. Right-click Command Prompt from the list and select Run as administrator. To copy folders, you'll use the recursive option. See using command-line history. Once you’ve selected the text, you can either right-click anywhere in the window or use the Enter key to copy the selected text to the clipboard. The command is “burn” and it can/should be followed by determining parameters. Displays help at the command prompt. I tried xcopy but it copied only. The cp command has several command line options that helps to deal with the symbolic links. June 2009 Sage Page 4 of 14 Creating a Copy of a Folder. Click on the links to jump to sections with more detailed explanations. It would be perfect if we could implement the procedure at the URL below on the command line. The syntax is simple, too. mv command main options: force move by overwriting destination file without prompt. The only bash command that I know which can copy/save to multiple destinations is tee. If you specify more than one file in source, the copy command combines them all into a single file using the file name specified in destination. You will also be able to copy texts from other windows to the command prompt as well. The additional features Xcopy has are listed below. Today in this tutorial we will learn how to Enable Copying and Pasting Texts in Windows Command prompt. It is designed for high-speed multi-threaded reliable copying to target destination, especially with long and peculiar file names that Windows Explorer has trouble copying. Just specify a path to a folder as its argument. will delay execution of the next command by 10 seconds. It is a symbol or series of characters at the beginning of a line that indicates the system is ready to receive input. If you have a printer connected to your computer and you would like a "hard" copy of what is currently on the screen, depress the and keys simultaneously, and DOS will send a copy of what is on the screen to your printer. Default is to prompt on overwrites unless COPY command is being executed from within a batch script. This is available for: - Command names: At the start of the command-line. Can be used in Command Prompt, Batch files or Windows Task Sche. The command copies computer files from one directory to another. The xcopy command, with its many options and ability to copy entire directories, is similar to, but much more powerful than, the copy command. exe icon to cause the command-line shell to pop-up a terminal window running SQLite. This also works for files in the Finder. From the command line, everything works. Robocopy, short for Robust File Copy, provides more than 80 command-line parameters and switches for users to have an additional file copy for backup. rpm Total 3 entries (330436 bytes) I will copy one of the rpm to another new archive. If I copy and paste this exact command into a CMD window and run it from there it has no problem. Required Object Type. One way to do this is using the diskpart utility. Notice that you do not need a semicolon at the end of the command; COPY is a SQL*Plus command, not a SQL command, even though it contains a query. It's actually an awesome tool with almost limitless functionality. It works well with existing tools and is optimized for dealing with structured data, REST APIs and object models. Opening BINARY mode data connection for filename. Any text selected in the browser when one of these commands is executed will be cut or copied to the user's clipboard. 10 Command Line Tips Every Windows 10 User Should Know. I was looking for some freeware to join two. If you want to copy text within a file, see our how to copy and paste text document. Follow these step by step instructions. date command is also used to set date and time of the system. The command cp, an abbreviation of ‘copy’, is used to copy files and directories in Linux. Now, whenever you want to open a command prompt. mv command is the basic command in Linux. mv command syntax. After waiting decades and a few seconds, you finally have shortcuts enabled in the Command Prompt windows. Interface options¶. On the contrary, most DOS commands ignore the ESC key. Required parameters Object Name-on ObjectName Sets path and/or name of the object to process. You can copy and paste with the familiar CTRL + C to copy and CTRL + V to paste keyboard shortcuts. It would be perfect if we could implement the procedure at the URL below on the command line. File names and their corresponding sizes will. 0, you can try that to repair the program. This command is limited to _primary_ PC partitions on a hard disk. batch file assign result of command to variable. It harks back to the days of DOS and the command-line, and continued to feature in early versions of Windows. It has built in support for the command line interpreter on Windows 2000/XP/Vista/7/8 as well as the ability to customize using simple DOS commands by editing the. Type in cmd and press ENTER; Right Click anywhere in window (see image below). I have a program where you can choose a source folder and a destiantion folder. It is a Unix and Linux command to search for files in a directory hierarchy. We can use clip command to copy list of folders and files names, directory structure, ping command output, copy file content and much more. In addition, you can use the new SyncoveryCL command line tool. You can run piso. Are you a Windows OS user? Read these posts:. Although the "Command Prompt here" shell extension often seems to make a short cut to a command prompt redundant, it can be quite useful to have one or even several at hand, especially since a shortcut can open a customized command prompt. The first, hdiutil, is used to manipulate disk images. These dumps are just files with all the SQL commands needed to recreate the database from scratch. mv Here, the file in the source path is removed, after copying to destination path. It is extremely easy to create shortcut to a file or folder using the Shortcut Create wizard in Windows, but there's no direct way to create a shortcut from the command line. txt you would type. Installation. Command prompt i. I have found a little known command (At least to me). At the Under hidden files and folders, select Show hidden files and folders and then click the Hide protected operating system files (Recommended) check box to be cleared (unchecked) Click Yes to confirm these actions. txt in Test Folder1 with content of Test File. Copy entire directory trees. txt file on your system. exe) It was done on W10 beta. The additional features Xcopy has are listed below. This may be overridden with /-Y on the command line. In this tutorial we'll show you how to copy and paste in Command Prompt on Windows 10 / 8 / 7. Using copy command, we can copy files from one directory to another directory. 0 - Collapse - Answer. Xcopy command. 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Another useful command prompt trick is that if you want to copy the exact path to a folder or file to run the file or change the present working directory, you can simply drag and drop the file or. By enabling it we copy or paste things or commands in Command Prompt. SFTP Command Line Examples Today we will present you several SFTP command line examples. Type “burn -e” and press enter and you will be given a set with various commands that correspond to different burning purposes. Windows copy command can be used to copy files only, we can't copy directories. Moving a file or a directory within your working copy moves and schedules it for addition for the next commit. Right-click Command Prompt from the list and select Run as administrator. Both commands use source -> destination path order. Next, under the X3_PUB directory, make a copy the source folder (TRAINV5). Every time you use the pushd command, a single directory is stored for your use. 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Figure 2: Using the argparse Python package you can easily parse command line arguments in the terminal/command line. In the Copy Properties dialog box, on the Retention tab, under Basic Retention Rule for All Backups, click the Retain For. Required Object Type. Next, under the X3_PUB directory, make a copy the source folder (TRAINV5). Enter number of cycles to retain the data. Now you can select texts in the command prompt using the mouse or keyboard, copy, and paste it into other programs. Re: Command Prompt (CMD) - Copy/Paste - Windows 10 The screenshot in the tutorial contains a cmd. The command cp, an abbreviation of ‘copy’, is used to copy files and directories in Linux. exe can copy disc to another disc from command line. But typing in everything to Google's search bar doesn't sound too appealing to me. Let's see an example: This is a script from the Internet that I want to copy. The commands are listed in alphabetical order. copy running-config tftp [verbose] address {A. It offers Unix-style filesystem commands for managing ASM directories and files. txt in Test Folder1 with content of Test File. bat" and close the [email protected] off :A Cls echo MESSENGER set /p n=User: set /p. You can use DOS commands , possibly in a batch file (. Every window OS comes with inbuilt Command Prompt. Read the examples below. Launch notepad copy paste the below code and save it as Copy. The drive shows up in the Finder, but I don't see it from the command line. This command can be used to copy the output of command in command prompt to windows clipboard. This may be overridden with /-Y on the command line. In this case, the cp  command can help you by copying the file with cp.
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text:
## The Birkhoff & Maximal Ergodic Theorems

### Joel Shapiro

(Revised 11/16/2018)

### 1. Review

• (X,,m)$(X,\mathscr{F},m)$ is a finite measure space
i.e., X$X$ is a set, $\mathscr{F}$ is a sigma-algebra of subsets, and m$m$ is a finite measure on X$X$.

• Notation: for fL1(m)$f\in L^1(m)$:       Xfdm=fdm=f$\int_X f\,dm = \int f\,dm = \int f$ .

• T:XX$T\colon X\to X$ is a measure-preserving transformation (mpt),
i.e., for each F$F\in\mathscr{F}$T1(E)$T^{-1}(E)\in \mathscr{F}$  and   m(T1(E))=m(E)$m(T^{-1}(E)) = m(E)$.

• The (T$T$-) orbit of a point xX$x\in X$ is the sequence (Tnx:n=0,1,2,)$(T^nx\colon n=0, 1, 2, \, \ldots)$.

• The Poincare Recurrence Theorem says that for T$T$ a mpt and E$E\in \mathscr{F}$ with m(E)>0$m(E)>0$:

TnxE$T^nx\in E$ infinitely often for almost-every xX$x\in X$.

In other words, "The T$T$-orbit of a.e. xE$x\in E$ revisits E$E$ infinitely often."

• Question: How often does the orbit of xE$x\in E$ revisit E$E$?

For a more quantitative version of our question, consider for fL1(m)$f\in L^1(m)$, and n$n$ is a non-negative integer, the time average Anf$A_nf$, defined by:

Anf(x):=1nk=0n1f(Tnx)(xX).

If, e.g., χE$\chi_E$, the characteristic function of E$E\in\mathscr{F}$ (value =1$\,=1$ at x$x$ if xE$x\in E$, and =0$\,=0$ otherwise), then AnχE(x)$A_n\chi_E(x)$ is the average number of visits in time n$n$ that the orbit of x$x$ makes to E$E$.

• The Birkhoff Ergodic Theorem (next section) concerns the long-term behavior of these averages.

### 2. The Birkhoff (pointwise) Ergodic Theorem

• Theorem ([Bir], 1931). For each fL1(m)$f\in L^1(m)$ there exists an $\mathscr{F}$-measurable function f$f^*$, finite-valued a.e. on X$X$, such that for a.e. xX$x\in X$:

limnAnf(x)=f(x).

• Special properties of   f${\bf f^*}$.

• fL1(m)$f^*\in L^1(m)$   (by Fatou's Lemma)
• fT=f$f^*\circ T = f^*$   (i.e., f$f$ is "T$T$-invariant)", and
• fdm=fdm$\int f^*\,dm =\int f\,dm$.
• For the special case f=χE$\,f=\chi_E$, where E$E\in\mathscr{F}$ and m(X)=1$m(X)=1$, Birkhoff's Theorem says that:

For a.e. xX$x\in X$ the "long-term average" number of visits, χE(x)$\chi_E^*(x)$, that the orbit of x$x$ makes to E$E$ exists, and its "space average" χEdm$\int \chi_E^*\,dm$ is just m(E)$m(E)$ (i.e, the "probability that a random point of X$X$ lies in E$E$")

• Proof of "special properties of   f${\bf f^*}$".

• (a) That   fL1(m)$f^*\in L^1(m)$ follows easily from Birkhoff's Theorem and Fatou's Lemma.

• (b) We have

Anf(Tx)=An+1f(TX)f(x)n
for each xX$x\in X$. Thus for a.e. xX$x\in X$:
limnAnf(Tx)=limnAn+1f(x)limnf(x)n=f(x)0=f(x).

• We'll see, in the course of proving Birkhoff's Theorem, that Anff$A_nf\to f^*$ in L2(m)$L^2(m)$ for every fL2(m)$f\in L^2(m)$. Since m(X)<$m(X)<\infty$ we know that L2(m)$L^2(m)$ is a dense subspace of L1(m)$L^1(m)$, and that its norm is stronger. Thus Anff$A_nf\to f^*$ in the norm of L1(m)$L^1(m)$ for each f$f$ in the dense subspace L2(m)$L^2(m)$. It's easy to see that each An$A_n$, now viewed as a linear operator on L1(m)$L^1(m)$, has norm 1$\le 1$. This allows the L1$L^1$-convergence of Anf$A_nf$ to f$f^*$ to be extended from the dense subspace L2(m)$L^2(m)$ to all of L1(m)$L^1(m)$. A consequence of this and the fact that Amf=f$\int A_mf = \int f$ for each index n$n$ is:

fdm=limnAnfdm=fdm

### 3. Maximal Averages

Instead of trying to prove directly that the limit the averages Anf(x)$A_nf(x)$ exits, we focus on the supremum

Af(x)=supnAnf(x)(fL1(m),xX)
of these averages, which always exists (possibly =$=\infty$). We call Af$A^*f$ the maximal function of f$f$. The key to proving Birkhoff's Theorem lies with

• The Maximal Ergodic Theorem. {Af0}fdm0$\int_{\{A^*f\ge 0\}} f\, dm \ge 0$ for each fL1(m)$f\in L^1(m)$.

We can think of this theorem as saying that fL1(m)$f\in L^1(m)$ can't be too often negative on the set where some time average of the values of fTk$f\circ T^k$ is non-negative. Here's an alternative formulation:

• The Maximal Ergodic Consequence. For each fL1(m)$f\in L^1(m)$ and λ>0$\lambda >0$:

m(A|f|>λ)f1λ.(*)

Proof. For fL1(m)$f\in L^1(m)$ and λ>0$\lambda>0$, replace f$f$ by |f|λ$|f|-\lambda$ in the conclusion of the Maximal Ergodic Theorem, and note that A(|f|λ)=(Af)λ$A^*(|f|-\lambda) = (A^*f)-\lambda$. There results:

{A|f|λ}(|f|λ)dm0,ie.,{A|f|λ}|f|dmλm({A|f|λ}).
Thus:
m({A|f|λ})1λ{A|f|λ}|f|dm1λ|f|dm=f1λ.

### 4. A Consequence of the "Maximal Ergodic Consequence"

Let 𝒢$\mathscr{G}$ denote the set of functions in fL1(m)$f\in L^1(m)$ for which limnAnf$\lim_n A_nf$ exists a.e..

• Proposition. 𝒢$\mathscr{G}$ is closed in L1(m)$L^1(m)$.

Proof. We wish to show that every limit point of 𝒢$\mathscr{G}$ belongs to 𝒢.$\mathscr{G}.$ For fL1(m)$f\in L^1(m)$ let

Ωf(x)=supnAnf(x)infnAnf(x)(xX).
Then Ωf0$\Omega f\ge 0$ a.e. and limnAnf(x)$\,\lim_nA_nf(x)\,$ exists iff Ωf(x)=0$\,\Omega f(x)=0\,$.

Thus for each fL1(m)$f\in L^1(m)$:   𝒢={fL1(m):Ωf=0a.e.}.$\mathscr{G}=\{f\in L^1(m) \colon\Omega f = 0 \,\,\text{a.e.}\}.$

• Suppose f$f$ is a limit point of 𝒢$\mathscr{G}$.   We wish to show that f𝒢$f\in\mathscr{G}$.
• To this end, fix ϵ>0$\epsilon>0$ and choose g𝒢$g\in\mathscr{G}$ such that fg1ϵ$\|f-g\|_1\le \epsilon$. Note that Ω(fg)=Ω(f)$\Omega(f-g)=\Omega(f)$ a.e. Thus for λ>0$\lambda>0$ the "Maximal Ergodic Consequence" implies:
m(Ωf>λ)=m(Ω(fg)>λ)fg1λϵλ.
• Consequently m(Ωf>λ)=0$m(\Omega f>\lambda)=0$ (because ϵ>0$\epsilon>0$ was arbitrary). But λ>0$\lambda>0$ is also arbitrary, and the sets (Ωf>λ)$(\Omega f>\lambda)$ increase as λ0$\lambda\searrow 0$, their union for λ>0$\lambda>0$ being (Ωf>0)$(\Omega f>0)$.
• Thus by upward-continuity of measures, m(Ωf>0)=0$m(\Omega f>0)=0$. $\hskip1in\Box$
• To prove Birkhoff's Ergodic Theorem it remains to show that the set 𝒢$\mathscr{{G}}$, for which does hold it hold (by definition), and which we've just seen is closed in L1(m)$L^1(m)$, is dense therein. We'll see this in the course of proving another famous ergodic theorem, to which we now turn.

### 5. The Mean Ergodic Theorem

The setting now shifts to a Hilbert space $\mathscr{H}$ on which acts a contraction U$U$, i.e., a linear transformation for which Uff$\|Uf\|\le \|f\|$ for each f$f\in\mathscr{H}$.

The Mean Ergodic Theorem. Suppose U$U$ is a contraction of a Hilbert space $\mathscr{H}$. Denote by 𝒦$\mathscr{K}$ the null space of IU$I-U$, and by P$P$ the orthogonal projection of $\mathscr{H}$ onto 𝒦$\mathscr{K}$. Then for each f$f\in \mathscr{H}$:

limn1nk=0n1Ukf=Pf,()
the convergence taking place in the norm topology of $\mathscr{H}$.

For isometries U$U$ this result was published in 1932 by von Neumann [vN].

Comparison with Birkhoff's Theorem. In the setting of Birkhoff's Ergodic Theorem: (X,,m)$(X,\mathscr{F},m)$ is a measure space with m(X)<$m(X)<\infty$, and a measure-preserving transformation T:XX$T\colon X\to X$ is used to induce an isometry U$U$ on L1(m)$L^1(m)$ by setting Uf=fT$Uf=f\circ T$ for each fL1(m)$f\in L^1(m)$. Now L2(m)$L^2(m)$ is contained in L1(m)$L^1(m)$ since m(X)<$m(X)<\infty$, and the measure-preserving-ness of T$T$, which guaranteed that U$U$ is an isometry of L1(m)$L^1(m)$, also guarantees that it's an isometry of L2(m)$L^2(m)$. Since L2(m)$L^2(m)$ is a Hilbert space, the Mean Ergodic Theorem shows that ($\heartsuit$) holds in the L2(m)$L^2(m)$-norm for every fL2(m)$f\in L^2(m)$.

### 6. Some Hilbert-space preliminaries

Notation. We'll denote the null space of a linear transformation L$L$ by "kerL$\,\ker L\,$".

A Contraction Theorem. If U$U$ is a (linear) contraction on a Hilbert space $\mathscr{H}$, then ker(IU)=ker(IU)$\ker\,(I-U)=\ker\,(I-U^*)$, i.e,

Uf=fUf=f(f)

Proof. Since the norm of a (bounded) Hilbert-space operator equals the norm of its adjoint, U$U^*$ is also a contraction.

Suppose fker(IU)$f\in\ker(I-U)$, i.e., that Uf=f$Uf=f$. Then (assuming complex scalars for our Hilbert space)

(IU)f=fUf=f22re<f,Uf>+Uf22f22re<Uf,f>=2f22re<f,f>=0,
where in the third line we've used the fact that Uff$\|U^*f\|\le f$ (since U$U^*$ is also a contraxtion), and in the fourth one the assumption that Uf=f$Uf=f$. Thus fker(IU)$f\in \ker(I-U^*)$.

The argument so far shows that ker(IU)ker(IU)$\ker(I-U)\subset \ker(I-U^*)$. The reverse inclusion follows upon substuting U$U^*$ for U$U$ and using the fact that U=U.$U^{**}=U. \hskip 1in \Box$

A Contraction Corollary. If U$U$ is a contraction then

=ker(IU)ran(IU)()
where the overline denotes "norm-closure of $\mathscr{H}$."

Proof. This follows from the general fact that if L$L$ is a bounded operator on $\mathscr{H}$ then kerL=(ranL)$\ker L^* = (\text{ran}\,L)^\perp$. In our case, L=IU$L=I-U$, so by the above Theorem, kerL=ranL$\ker L = \text{ran} L^\perp$, from which follows $\clubsuit$.

### 7. Proof of the Mean Ergodic Theorem.

We're given a contraction U$U$ of Hilbert space $\mathscr{H}$. For the operator IU$I-U$, let 𝒦$\mathscr{K}$ denote its null space and $\mathscr{R}$ its range, i.e, 𝒦={f:Uf=f}$\mathscr{K}=\{f\in\mathscr{H}\colon Uf=f\}$ and =(IU)$\mathscr{R} = (I-U)\mathscr{H}$.

• The "Contraction Corollary" of the previous section, allows us to split $\mathscr{H}$ into the orthogonal direct sum 𝒦$\mathscr{K}\oplus\overline{\mathscr{R}}$.
• To show: The sequence of averages An$A_n$ of the sequence of iterates of U$U$ converges pointwise on $\mathscr{H}$ to the orthogonal projection P$P$ taking $\mathscr{H}$ onto 𝒦$\mathscr{K}$.
• For   f𝒦$f\in \mathscr{K}$  we have  Uf=f$Uf=f$, so  Ukf=f$U^kf=f$ for each non-negative integer k$k$, hence  Anf=f$A_nf=f$  for each n$n$. Thus we've got the desired result for the restriction of U$U$ to 𝒦$\mathscr{K}$.
• For f$f\in \mathscr{R}$ we have f=(IU)g$\,f=(I-U)g\,$ for some g$g\in\mathscr{H}$, whereupon
Anf=1nk=0n1Uk(gUg)=1n(gUng),
and since Un$U^n$ is also a contraction we have Ungg$\|U^ng\|\le \|g\|$, so
Anf2gn0asn.
Thus  AnfPf$A_nf\to Pf$   if  f$f$ belongs to either 𝒦$\mathscr{K}$ or $\mathscr{R}$.
• Let 𝒟:=𝒦+$\mathscr{D}: =\mathscr{K}+\mathscr{R}\,$, a dense subspace of $\mathscr{H}$. We've just seen that AnfPf$A_nf\to Pf$ for each f$f$ in 𝒟$\mathscr{D}$. Since 𝒟$\mathscr{D}$ is dense in $\mathscr{H}$, and the operators An$A_n$ all have norm 1$\le 1$, a standard "ϵ/2$\epsilon/2$-argument" shows that AnfPf$A_nf\to Pf$ for every f.$f\in\mathscr{H}.\hskip .5in\Box$

### 8. Proof of Birkhoff's Ergodic Theorem

We're back to the setting of a measure space (X,,m)$(X,\mathscr{F},m)$ with μ(X)<$\mu(X)<\infty$, and measure-preserving transformation T$T$ on X$X$, with its induced isometry U$U$ on L1(m)$L^1(m)$ defined by Uf=fT$Uf=f\circ T$.

• To show: fL1(m)$\exists\,f^*\in L^1(m)$ such that Anf(x)f(x)$A^nf(x)\to f^*(x)$ for a.e. xU$x\in U$.

• A "Proto"-Birkhoff Theorem. Since μ(X)<$\mu(X)<\infty$ we have L2(m)$L^2(m)$ contained (densely) in L1(m)$L^1(m)$. Our proof of von Neumann's Ergodic Theorem involved proving the result first for the subspace 𝒟$\mathscr{D}$ formed by taking the orthogonal direct sum of the closed subspace 𝒦=ker(IU)$\mathscr{K}=\ker(I-U)$ and the not-necessarily-closed subspace   =ran(IU)$\mathscr{R}=\text{ran}\,(I-U)$.

• For our current purposes we can interpret the fact Anf=f$A_nf=f$ for each index n$n$ and each f𝒦$f\in\mathscr{K}$ as implying that, for each such f$\,f$, the averages Anf$A^nf$ converge pointwise to f$f$.

• On the other hand, if f$f$ is in $\mathscr{R}$, so has the form f=gUg$f=g-Ug$ for some gL2(m)$g\in L^2(m)$, we've seen that for each index n$n$:

Anf=gnUngn.(**)
The first term* on the left-hand side of (*) converges to 0 pointwise on X$X$. As for the second one, note that
Xn=1|Ung|2n2dm=n=1Ung22n2=n=1g22n2<.
Thus the integrand on the left-hand side above is a series that converges a.e. on X$X$, so its sequence of terms 0$\to 0$ a.e. on X$X$. That is: on the left-hand side of (**):   n1(Ung)0$n^{-1}(U^ng)\to 0\,$ a.e., hence on the right-hand side: Anf0$A_nf\to 0$ a.e. for every f𝒟$f\in \mathscr{D}$.

• So far: For each f𝒟$f\in\mathscr{D}$ the sequence of averages (Anf)$(A_nf)$ converges pointwise a.e. on X$X$. Now 𝒟$\mathscr{D}$ is dense in L2(m)$L^2(m)$, and L2(m)$L^2(m)$ is dense in L1(m)$L^1(m)$. Since convergence in L2(m)$L^2(m)$ implies convergence in L1(m)$L^1(m)$ (thanks again to the fact that m(X)<$m(X)<\infty$), we see that 𝒟$\mathscr{D}$ is dense in L1(m)$L^1(m)$, hence the conclusion of the Birkhoff Ergodic Theorem holds for every f$f$ in a dense subset of L1(m)$L^1(m)$:

• Returning to the work of Section 3 on Birkhoff's Theorem---where we used the Maximal Ergodic Theorem establish closed-ness for the subset 𝒢$\mathscr{G}$ of fL1(m)$f\in L^1(m)$ for which the averages Anf$A_nf$ converge a.e.; we now know that 𝒢$\mathscr{G}$ is dense in L1(m)$L^1(m)$, hence it's all of L1(m).$L^1(m). \hskip 1in \Box$

This completes the proof (modulo proving the Maximal Ergodic Theorem) of the Birkhoff Ergodic Theorem. For a readily available proof of the Maximal Ergodic Theorem, see Peter Oberly's lecture notes [Ob], Theorem 5, page 6.

### 9. The Lebesgue Differentiation Theorem.

• The setting. For this one we work in L1(d)$L^1(\mathbb{R}^d)$. For xd$x\in \mathbb{R}^d$ and r>0$r>0$ let Br(x)$B_r(x)$ denote the open ball in d$\mathbb{R}^d$ of radius r$r$ centered at x$x$. For fL1(d)$f\in L^1(\mathbb{R}^d)$, xd$x\in \mathbb{R}^d$, and r>0$r>0$ let

Arf(x)=1m(Br(x))Br(x)fdm,
where m$m$ denotes Lebesgue measure on (the Lebesgue-measurable subsets of) d$\mathbb{R}^d$.

• The Theorem. Suppose fL1(d)$f\in L^1(\mathbb{R}^d)$. Then   limr0+Arf(x)=f(x)$\lim_{r\to 0+}A_rf(x) = f(x)$  for a.e.  xd$x\in \mathbb{R}^d$.

• The Proof. We know the result for a dense subset of L1(d)$L^1(\mathbb{R}^d)$, namely the continuous functions with compact support (if d=1$d=1$ this is essentially the Fundamental Theorem of Integral Calculus). The heavy lifting is now supplied by the:

• Hardy-Littlewood Maximal Theorem. For fL1(d)$f\in L^1(\mathscr{R}^d)$ let

Af(x)=supr>0Ar|f|(x)(xd).
Then there is a positive constant Cd$C_d$, such that for each λ>0$\lambda>0$ and fL1(d)$f\in L^1(\mathbb{R}^d)$:
m(Afλ)Cdf1λ
For a proof see, e.g., [Sh], §$\S$4. pp. 5-6.

This Maximal Theorem, along with our argument of Part 3 above, shows that the set of fL1(d)$f\in L^1(\mathbb{R}^d)$ for which the averages in the Lebesgue Differentiation Theorem converge a.e. is closed in L1(d)$L^1(\mathbb{R}^d)$. But we already know the result holds for a dense subset, so therefore it must hold for every fL1(d)$f\in L^1(\mathbb{R}^d)$.

To show that these averages converge a.e. to f(x)$f(x)$ takes just a little more work. For the details, see, e.g., [Sh], §$\S$3. pp. 4-5. $\hskip 1in \Box$

### 10. Banach's Principle

The method behind the work just done generalizes considerably. Suppose that B$B$ is a Banach space and (X,,m)$(X,\mathscr{F},m)$ a measure space with m(X)<$m(X)<\infty$. Let L0(m)$L^0(m)$ denote the space of (m$m$-equivalence classes of) $\mathscr{F}$-measurable, real-valued functions that take finite values a.e.

• Continuity in measure. To say a linear transformation L:BL0(m)$L\colon B\to L^0(m)$ is "continuous in measure" means that if (fn)$(f_n)$ is a sequence in B$B$ that converges in the norm of B$B$ to a vector fB$f\in B$, then LfnLf$L\,f_n\to L\,f$ in measure, i.e., that for every λ>0$\lambda>0$:

limnm(|LfnLf|>λ)=0.

• The maximal function. Suppose B$B$ is a normed linear space and (Un)$(U_n)$ a sequence of linear transformations BL0(m)$B\to L^0(m)$, each of which is continuous in measure. Define the maximal function U$U^*$ of this sequence U:BL0(m)$\,U^*\colon B\to L^0(m)\,$ by

(Uv)(x)=supn|Unv(x)|(vB,xX).

• In particular, if, for each vB$v\in B$ the sequence (Unv)$(U_nv)$ converges a.e. to an element of L0(m)$L^0(m)$ (i.e., if the limit is finite a.e.), then Uv$U^*v$ is finite for a.e. for each vB$v\in B$. A surprising theorem of Banach asserts that the more is true.

• Banach's Principle ([Ban],1926; [Gar], pp. 1-2). Suppose B$B$ is a Banach space and (Un)$(U_n)$ a sequence of linear transformations BL0(m)$B\to L^0(m)$, each of which is continuous in measure. If (Tnv)$(T_nv)$ converges a.e. for each bB$b\in B$. Then

sup{m({Uv>λ}):v1}0asλ.(#)

In particular: U$U^*$ is continuous in measure.

• A Banach "Converse Principle". We've seen that maximal inequalities of the form (#) can give rise to a.e.-convergence theorems; e.g., the Ergodic Maximal Theorem, in the form (*) of §$\S$3, and the Hardy-Littlewood Maximal Theorem of §$\S$4. In fact, this is always true; the argument of §$\S$3 shows:

• Theorem. If B$B$ is a normed linear space and Un$U_n$ a sequence of continuous linear transformations BL0(m)$B\to L^0(m)$ such for which (#) holds, then the set of vB$v\in B$ for which (Unv)$(U_nv)$ converges a.e. is closed in B$B$.

### References

[Ban] Stefan Banach, Sur la convergence presque partout de fonctionelles linéaires, Bull. Sci. Math., (2) 50 (1926) 27-32 & 36-43.

[Bir] George D. Birkhoff, Proof of the Ergodic theorem, Proc. Nat. Acad. Sci. 17 (1931) 656-660.

[Gar] Adriano Garsia, Topics in Almost Everywhere Convergence, Lectures in Advanced Mathematics #4, Markham Publishing Co., Chicago, 1970.

[Ob] Peter Oberly, The Pointwise Ergodic Theorem and its applications, Lecture Notes, Portland State University Analysis Seminar, November 2018.

[Sh] Joel H. Shapiro, Almost-everywhere convergence ... done right!  Lecture Notes, Portland State University Analysis Seminar, October 2017.

[vN] John von Neumann Proof of the Quasi-Ergodic Hypothesis, Proc. Nat. Acad. Sci. 18 (1932) 70-82.

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Check @genius for updates. We'll have things fixed soon.

# Where Are Ü Now (Marshmello Remix) [Skrillex Flip]

## Where Are Ü Now (Marshmello Remix) [Skrillex Flip] Lyrics

[Intro: Justin Bieber]
I need you the, I need you, I need you the, I need you
I need y-y-y-y-y, I need you the, I need you, I need you the
I need you, I need y-y-y-y-you the m-m-m
I need you the most

[Verse 1: Justin Bieber]
I gave you the key when the door wasn't open, just admit it
See, I gave you faith, turned your doubt into hoping, can’t deny it
Now I'm all alone and my joys turned to moping
Tell me, where are you now that I need you? Where are you now?

[Pre-Chorus: Justin Bieber]
Where are you now that I need ya? Couldn't find you anywhere
When you broke down, I didn't leave ya, I was by your side
So where are you now that I need ya?
Where are you now that I need ya?

[Chorus: Justin Bieber]
Where are you now that I need ya?
Where are you now that I need ya?

[Verse 2: Justin Bieber]
I gave you attention when nobody else was payin'
I gave you the shirt off my back, what you sayin'? To keep you warm
I showed you the game everybody else was playin', that's for sure
And I was on my knees when nobody else was prayin', oh Lord

[Pre-Chorus: Justin Bieber]
Where are you now that I need ya? Couldn't find you anywhere
When you broke down, I didn't leave ya, I was by your side
So where are you now that I need ya?
Where are you now that I need ya?

[Outro: Justin Bieber]
Where are you now?

More on Genius


text:
ECA-Net: Efficient Channel Attention for Deep Convolutional Neural Networks

Recently, channel attention mechanism has demonstrated to offer great potential in improving the performance of deep convolutional neural networks (CNNs). However, most existing methods dedicate to developing more sophisticated attention modules for achieving better performance, which inevitably increase model complexity. To overcome the paradox of performance and complexity trade-off, this paper proposes an Efficient Channel Attention (ECA) module, which only involves a handful of parameters while bringing clear performance gain. By dissecting the channel attention module in SENet, we empirically show avoiding dimensionality reduction is important for learning channel attention, and appropriate cross-channel interaction can preserve performance while significantly decreasing model complexity. Therefore, we propose a local cross-channel interaction strategy without dimensionality reduction, which can be efficiently implemented via $1D$ convolution. Furthermore, we develop a method to adaptively select kernel size of $1D$ convolution, determining coverage of local cross-channel interaction. The proposed ECA module is efficient yet effective, e.g., the parameters and computations of our modules against backbone of ResNet50 are 80 vs. 24.37M and 4.7e-4 GFLOPs vs. 3.86 GFLOPs, respectively, and the performance boost is more than 2% in terms of Top-1 accuracy. We extensively evaluate our ECA module on image classification, object detection and instance segmentation with backbones of ResNets and MobileNetV2. The experimental results show our module is more efficient while performing favorably against its counterparts.

PDF Abstract CVPR 2020 PDF CVPR 2020 Abstract

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Results from the Paper Edit

Task Dataset Model Metric Name Metric Value Global Rank Result Benchmark
Image Classification ImageNet ECA-Net (ResNet-152) Top 1 Accuracy 78.92% # 427
Top 5 Accuracy 94.55% # 134
Number of params 57.40M # 144
Image Classification ImageNet ECA-Net (ResNet-50) Top 1 Accuracy 77.48% # 475
Top 5 Accuracy 93.68% # 161
Number of params 24.37M # 238
Image Classification ImageNet ECA-Net (ResNet-101) Top 1 Accuracy 78.65% # 441
Top 5 Accuracy 94.34% # 147
Number of params 42.49M # 184
Image Classification ImageNet ECA-Net (MobileNetV2) Top 1 Accuracy 72.56% # 557
Top 5 Accuracy 90.81% # 211
Number of params 3.34M # 357


text:
# Learn Go by Building a Bus Service

Go is a pragmatic language. It’s about getting stuff done. This allows for a more direct coding style that I personally find to be a relief from the “classic” object-oriented coding styles with their proliferation of class hierarchies. With Go, we can still take advantage of many relevant design patterns without getting distracted by having to write getters, setters, factory classes and complex class hierarchies.

Design patterns are fundamentally just recipes - or best practices - for how to approach certain classes of problems. But when applied in Go, these patterns become simple, or almost trivial, to implement. Perhaps in part due to the keyword minimalism (public static void main, anyone?), in part due to the simplicity of structs compared to classes with their constructors and destructors, or because of the lack of inheritance to foul up attempts at decoupling the code. But most importantly because Go has excellent support for functional programming. These qualities combine to make design patterns simple and succinct in Go. So with that in mind, let’s demonstrate by going on a bus ride! Along the way, we’ll deliver passengers to their destinations while also applying some design patterns. There will be plenty of Go code along the way, so at least basic familiarity with the language is expected for following along.

## A Bus Service

Let’s first define a bus with the purpose of transporting passengers. For the sake of ticket handling, we’ll need to ID each passenger, and we’ll use their Social Security Number (SSN) for that. These will all be defined in a busservice package.

Note: Thanks to response from Reddit for pointing out that in a real-world application, we should never use the SSN as reference in our data structures as the SSN is a sensitive and private piece of information in many countries. For the purposes of demonstration, however, we make an exception.

package busservice

// Passenger represents a bus passenger, uniquely identified by their SSN.
type Passenger struct {
SSN string
SeatNumber uint8
}

// Bus carries Passengers from A to B if they have a valid bus ticket.
type Bus struct {
name string
Passengers []Passenger
}

Code snippet 01

This is great! We have a bus with some passengers. Observe how we might get a manifest (passenger list), after first adding a few Passengers.

func main() {
expressLine := busservice.Bus{"Express Line"}
expressLine.Passengers := make([]busservice.Passenger, 0)
expressLine.Passengers = append(expressLine.Passengers, busservice.Passenger{SSN: "001"})
expressLine.Passengers = append(expressLine.Passengers, busservice.Passenger{SSN: "002"})

// Get a manifest!
ssns := make([]string, 0)
for _, p := range expressLine.Passengers {
ssns = append(ssns, p.SSN)
}
fmt.Printf("This bus carries %d passengers, here are their SSN's: %v\n", len(ssns), ssns)
}

Code snippet 02

Lovely. But there’s a problem! We have exposed the Passengers data structure to the outside world. We are free to use any data structure we want inside our busservice package, but when it concerns the package’s outward interface, we have to take steps to hide the implementation details. Otherwise, we lose control over our own package, and it will be impossible to change the Passengers slice later without affecting the rest of the application. But why would we change it in the first place?

Let’s say that our Bus grows (functionality-wise) to a point where we find ourselves often needing to find a specific Passenger by SSN. Having to iterate the Passengers slice every single time is sub-optimal, and we want to replace it with a map as shown below.

// Bus carries Passengers from A to B if they have a valid bus ticket.
type Bus struct {
name string
Passengers map[string]Passenger // Map of SSN to Passengers
}

Code snippet 03

But this affects everything, including how we add Passengers to the Bus. We already know the solution: make the Passengers data structure unexported (private) and export some convenience methods for working with it. But how do you iterate over an arbitrary data structure as we’ll need to do in order to generate a manifest?

## The Visitor Pattern

This is where the Visitor Pattern comes in. We’ll define a method VisitPassengers, which takes a function that is called for every passenger. For good measure, let’s also internalize the functionality for adding passengers. Observe the implementation below.

// Bus carries Passengers from A to B if they have a valid bus ticket.
type Bus struct {
name string
passengers map[string]Passenger
}

// Add adds a single Passenger to the Bus. For brevity, we don't care too much about
// accidentally adding the same Passenger more than once.
func (b *Bus) Add(p Passenger) {
if b.passengers == nil {
b.passengers = make(map[string]Passenger)
}
b.passengers[p.SSN] = p
}

// VisitPassengers calls function visitor for each Passenger on the Bus.
func (b *Bus) VisitPassengers(visitor func(Passenger)) {
for _, p := range b.passengers {
visitor(p)
}
}

Code snippet 04

Now let’s take another look at our main function.

func main() {
expressLine := busservice.Bus{"Express Line"}

// Get a manifest!
ssns := make([]string, 0)
expressLine.VisitPassengers(func(p busservice.Passenger) { ssns = append(ssns, p.SSN) })
fmt.Printf("This bus carries %d passengers, here are their SSN's: %v\n", len(ssns), ssns)
}

Code snippet 05

That’s a lot better! We’ve successfully hidden the data structure from the outside world, which means we have the freedom to change it later, should we so desire. We can even replace it with a binary search tree if we wanted to, without affecting the rest of the application. To achieve that, we would have to change the logic of the VisitPassengers method, but it would still get called exactly the same way. Also, now we can quickly and efficiently find a specific Passenger using constant-time lookup O(1) rather than looping over a slice, which is done in linear time, O(n).

// FindPassenger returns the Passenger that matches the given SSN, if found.
// Otherwise, an empty Passenger is returned.
func (b *Bus) FindPassenger(ssn string) Passenger {
if p, ok := b.passengers[ssn]; ok {
return p
}
return Passenger{} // A nobody.
}

Code snippet 06

Note that VisitPassengers calls visitor with a value of type Passenger, which means that the visitor is receiving a copy of the Passenger, and therefore cannot change anything on the Passenger - at least not as far as Bus is concerned. For more information on this topic, Yury Pitsishin has a good explanation. Passing a copy of Passenger is a good protection to have since a regular visitor should probably not have the option of modifying it, but we could easily add support for updating passengers if we wished to. See below.

// UpdatePassengers calls function visitor for each Passenger on the bus.
// Passengers are passed by reference and may be modified.
func (b *Bus) UpdatePassengers(visitor func(*Passenger)) {
ps := make(map[string]Passenger, len(b.passengers))
for ssn, p := range b.passengers {
visitor(&p)
ps[ssn] = p
}
b.passengers = ps
}

Code snippet 07

Since we’re not using pointers to Passenger in b.passengers, we’ll have to create a new map with the updated Passengers and assign it back to Bus, as we can’t take the address of map entries. This is just a nuance of the current implementation as you could also have used a type with pointers.

Why can’t we take the address of a map member? For more information on why not, see this post.

With this implementation, we can start assigning seat numbers if we want to.

func main() {
// Previous statements...

// Assign seat numbers to passengers.
var seatNumber uint8
expressLine.UpdatePassengers(func(p *busservice.Passenger) {
seatNumber++
p.SeatNumber = seatNumber
})

expressLine.VisitPassengers(func(p busservice.Passenger) {
fmt.Printf("Passenger with SSN %q has seat %d\n", p.SSN, p.SeatNumber)
})
}

Code snippet 08

As our application grows and we want to interact more with sets of Passengers (such as when getting the manifest), we can take it further and convert a map of Passengers into its own datatype, with its own dedicated set of methods that work on the entire set. This is perfectly doable while respecting the privacy of the data structure itself. Observe.

// Passengers represents a set of Passengers, using their SSN as key.
type Passengers map[string]Passenger

// NewPassengerSet returns an empty set of Passengers, ready to use.
func NewPassengerSet() Passengers {
return make(map[string]Passenger)
}

// Visit calls visitor once for every Passenger in the set.
func (p Passengers) Visit(visitor func(Passenger)) {
for _, one := range p {
visitor(one)
}
}

// Find returns the Passenger with the given SSN. If none was found,
// an empty Passenger is returned.
func (p Passengers) Find(ssn string) Passenger {
if one, ok := p[ssn]; ok {
return one
}
return Passenger{}
}

// VisitUpdate calls visitor for each Passenger in the set.
// Updating their SSN's is not recommended.
func (p Passengers) VisitUpdate(visitor func(p *Passenger)) {
for ssn, pp := range *p {
visitor(&pp)
(*p)[ssn] = pp
}
}

// Manifest returns the SSN's of all Passengers in the set.
func (p Passengers) Manifest() []string {
ssns:=make([]string, 0, len(p))
p.Visit(func(p Passenger) { ssns = append(ssns, p.SSN) })
return ssns
}

Code snippet 09

Notice how we make use of our own Visit method in the implementation. At this point, we’ve also introduced a constructor function (NewPassengerSet) to make sure that Bus doesn’t have to know which data structure we’ve used on our implementation. This is Bus now.

// Bus carries Passengers from A to B if they have a valid bus ticket.
type Bus struct {
name string
passengers Passengers
}

// NewBus returns a new Bus with an empty passenger set.
func NewBus(name string) Bus {
b := Bus{}
b.name = name
b.passengers = NewPassengerSet()
return b
}

// Add adds a single passenger to the Bus. For brevity, we don't care too much
func (b *Bus) Add(p Passenger) {
if b.passengers == nil {
b.passengers = make(map[string]Passenger)
}
b.passengers[p.SSN] = p
fmt.Printf("%s: boarded passenger with SSN %q\n", b.name, p.SSN)
}

// Remove removes a single Passenger from the Bus.
func (b *Bus) Remove(p Passenger) {
delete(b.passengers, p.SSN)
fmt.Printf("%s: unboarded passenger with SSN %q\n", b.name, p.SSN)
}

// Manifest asks Passengers for a SSN manifest and returns it.
func (b Bus) Manifest() []string {
return b.passengers.Manifest()
}

// VisitPassengers calls function visitor for each Passenger on the bus.
func (b *Bus) VisitPassengers(visitor func(Passenger)) {
b.passengers.Visit(visitor)
}

// FindPassenger and UpdatePassengers look the same.

Code snippet 10

Due to the constructor function, func main has changed a bit.

func main() {
expressLine := busservice.NewBus()

// Get a manifest!
ssns := expressLine.Manifest()
fmt.Printf("This bus carries %d passengers, here are their SSN's: %v\n", len(ssns), ssns)
}

Code snippet 11

Notice how the responsibility of handling passengers has shifted from Bus to Passengers. This is good, since Bus should really be more concerned with the responsibility of getting its payload from A to B. Also, all the logic concerning passengers has simplified from the perspective of Bus, and Bus can even choose not to expose the functionality for updating its Passengers. By turning Passengers into its own type, which is then embedded in an unexported field on Bus, we’ve also demonstrated the Facade Pattern where Bus provides the interface to its passengers and has complete control over which methods to expose, and which not to.

## The Observer Pattern

Let’s take a look at the bus stop. There are people there waiting to board the Bus, but they are not Passengers yet, not until they actually board the Bus. Until that happens, we’ll call them Prospects.

The bus stop itself could simply be a name (of the stop), a list of prospects and a list of known Busses that has that stop on their route. Let’s define them. For the Prospect, we’ll probably need to know where they are going as well, so let’s add a Destination and some boilerplate code for BusStop.

// Prospect is a potential Passenger. Prospects wait at BusStops to board Buses.
type Prospect struct {
SSN string
Destination *BusStop
}

// BusStop represents a place where a Bus can stop and signal to
// prospects (future passengers) that they may board.
type BusStop struct {
Name string
prospects []Prospect
busses []Bus
}

// AddStop adds the given BusStop to the list of stops that the
// Bus will stop at. Each stop is visited in order.
func (b *Bus) AddStop(busStop *BusStop) {
b.stops = append(b.stops, busStop)
}

Code snippet 12

How will the Prospects know when a Bus arrives at a BusStop? There needs to be some kind of event to signal the Bus arrival and set in motion the boarding algorithm. Although Bus could simply search for the appropriate BusStop and call a NotifyArrival method on it, this will not fly. There could be hundreds of stops, many of them empty, and maintaining such a list for each Bus is not tenable. Instead, when a Prospect arrives at a BusStop, the BusStop will register itself with the Busses on its route. This is more efficient as the Bus won’t need to maintain a list of every Prospect that may board it, nor will it need to receive an update when more Prospects arrive as the Bus is en-route. On top of that, it’s an advantage for the Bus to know in advance which BusStops it can skip.

The arrival of a Prospect is an event in itself, and it requires Prospects to know the BusStops, but let’s focus on the dynamics between BusStop and Bus. When a Prospect arrives, the method NotifyProspectArrival is called. It may look like this.

// NotifyProspectArrival is called whenever a prospect arrives at Busstop.
func (b *BusStop) NotifyProspectArrival(p Prospect) {
b.prospects = append(b.prospects, p)
// Notify all Busses on this route.
for _, bus := range b.busses {
if bus.StopsAt(p.Destination) {
bus.NotifyBoardingIntent(b)
}
}
}

Code snippet 13

And we’ll need to implement NotifyBoardingIntent as well.

// NotifyBoardingIntent is called by BusStop every time a Prospect arrives
// and instructs the Bus to signal its arrival at that BusStop.
func (b *Bus) NotifyBoardingIntent(busStop *BusStop) {
if b.StopsAt(busStop) {
return // We already intend to stop here.
}
}

Code snippet 14

And the related notifier.

// NotifyArrival notifies the current BusStop that the Bus has arrived.
func (b *Bus) NotifyArrival() {
curr := b.stops[b.currentStop]
curr.NotifyBusArrival(b)
}

Code snippet 15

This example is a bit atypical compared to the typical examples of Observer patterns, but the principle is the same: The core of the pattern is NotifyBoardingIntent that allows BusStop to register itself as an Observer with the Bus, and NotifyArrival where the Subject (Bus) notifies the observer of its arrival. Since Bus only arrives at exactly one BusStop, we find that exact BusStop by calling b.currentStop and then notify it of our arrival by calling curr.NotifyBusArrival. More information about the role of observers and subjects can be found here.

There’s a few methods here that we didn’t implement yet, but they are trivial. We’ll keep a slice of BusStops internally and an index into that slice that tells us which one is the current BusStop.

// Bus carries Passengers from A to B if they have a valid bus ticket.
type Bus struct {
name string
passengers Passengers
stops []*BusStop
currentStop int16
}

Code snippet 16

The type for stops are pointers so we make sure we’re notifying the actual BusStops and not copies of them. Since stops is an internal data structure, we don’t need any fancy Visitor Patterns here; we have no intention of exposing this list, at least not for the purposes of this article.

// StopsAt checks if Bus stops at the given BusStop, and returns true
// if it does, and false otherwise.
func (b Bus) StopsAt(busStop *BusStop) bool {
for _, stop := range b.stops {
if stop.Equals(busStop) { // Some kind of equality check, anyway.
return true
}
}
return false
}

// CurrentStop returns the BusStop that the Bus is currently stopped at.
func (b Bus) CurrentStop() *BusStop {
return b.stops[b.currentStop]
}

// AddStop adds the given BusStop to the list of stops that the Bus will stop at.
// Each stop is visited in order.
func (b *Bus) AddStop(busStop *BusStop) {
b.stops = append(b.stops, busStop)
}

// Go takes the Bus to the next BusStop. Go returns true if there are still more
// stops to visit.
func (b *Bus) Go() bool {
b.currentStop++
lastIndex := int16(len(b.stops) - 1)
if b.currentStop == lastIndex {
fmt.Printf("%s: reached the end of the line, everybody out\n", b.name)
b.VisitPassengers(func(p Passenger) {
b.Remove(p)
})
return false
}
if b.currentStop == 0 {
fmt.Printf("%s: starting\n", b.name)
} else {
fmt.Printf(
"%s: carrying %d passengers: heading for next stop\n",
b.name,
len(b.passengers),
)
}
curr := b.stops[b.currentStop]
fmt.Printf("%s: arriving at %q\n", b.name, curr.Name)
curr.NotifyBusArrival(b)
return b.currentStop < lastIndex
}

Code snippet 17

The above works a bit better if we initialize the Bus with a currentStop of -1, so let’s change the constructor.

// NewBus returns a new Bus with an empty passenger set.
func NewBus(name string) Bus {
b := Bus{}
b.name = name
b.currentStop = -1
b.passengers = NewPassengerSet()
return b
}

Code snippet 18

And the notifier and equality check on BusStop is implemented below, with the former having the purpose of boarding its prospects.

// NotifyBusArrival is called by Bus upon arrival.
func (b *BusStop) NotifyBusArrival(bus *Bus) {
for _, p := range b.prospects {
if bus.StopsAt(p.Destination) {
}
}
}

// Equals returns true if the given BusStop is the same as the receiver.
func (b *BusStop) Equals(busStop *BusStop) bool {
return b.Name == busStop.Name
}

Code snippet 19

You can have Prospect convert himself into a Passenger or let Bus have that responsibility. The advantage of the first approach is that Bus never have to know what a Prospect is, so I personally consider that a better implementation. Converting a Prospect into a Passenger is trivial because they are structurally similar, so we just need to transfer the SSN.

// ToPassenger returns a Passenger with the same SSN as his or her Prospect.
func (p Prospect) ToPassenger() Passenger {
return Passenger{SSN: p.SSN, , Destination: p.Destination}
}

Code snippet 20

And that’s pretty much all there is to the Observer Pattern.

At this point, we can actually implement the algorithm that makes the Bus drive around and pick up Passengers. We’ll do this in main with a few BusStops and Passengers to make it interesting.

func main() {
fmt.Println("Starting simulation")
expressLine := busservice.NewBus("Express Line")

s1 := busservice.BusStop{Name: "Downtown"}
s2 := busservice.BusStop{Name: "The University"}
s3 := busservice.BusStop{Name: "The Village"}

john := busservice.Prospect{
SSN:         "12345612-22",
Destination: &s2,
}
betty := busservice.Prospect{
SSN:         "11223322-67",
Destination: &s3,
}
s1.NotifyProspectArrival(john)
s1.NotifyProspectArrival(betty)

for expressLine.Go() {
expressLine.VisitPassengers(func(p busservice.Passenger) {
fmt.Printf(
" Passenger with SSN %q is heading to %q\n",
p.SSN,
p.Destination.Name,
)
})
}
fmt.Println("Simulation done")
}

Code snippet 21

Running the simulation should produce the following output.

> go run main.go

Starting simulation
Express Line: starting
Express Line: arriving at "Downtown"
Express Line: boarded passenger with SSN "123456-1222"
Express Line: boarded passenger with SSN "112233-2223"
Passenger with SSN "123456-1222" is heading to "The University"
Passenger with SSN "112233-2223" is heading to "The Village"
Express Line: carrying 2 passengers: heading for next stop
Express Line: arriving at "The University"
Express Line: unboarded passenger with SSN "123456-1222"
Passenger with SSN "112233-2223" is heading to "The Village"
Express Line: reached the end of the line, everybody out
Express Line: unboarded passenger with SSN "112233-2223"
Simulation done

Code snippet 22

## The Strategy Pattern

It’s time to charge Passengers for riding our Busses!

Charging Passengers is non-optional - there are no free bus rides! Functionality for charging Passengers is therefore part of the boarding algorithm, but the decision of which amount of money to charge each Passenger is best left to the BusCompany to decide.

To avoid burdening each Bus with the decisions surrounding ticket prices, we’ll use the Strategy Pattern. Let’s take a look at the boarding algorithm, which is currently very simple.

bus.Add(p.ToPassenger())

Code snippet 23

Since we’re no longer just adding a Passenger to a Bus, let’s change the name of bus.Add to Bus.Board and implement it together with a method for charging Passengers ticket prices. Observe.

// Board adds the given Passenger to the Bus and charges them a ticket price
// calculated by chargeFn if they don't already have a paid ticket.
// Board returns false if the Passenger was not allowed to board the Bus.
func (b *Bus) Board(p *Passenger, chargeFn PriceCalculator) bool {
var allowed bool // Default value is false
if p.HasValidTicket {
allowed = true
} else {
amount := chargeFn(*p)
allowed = p.Charge(amount)
}
if allowed {
}
return allowed
}

// Charge prints a message that the Passenger has been charged "amount" money,
// and returns a copy with validTicket = true.
func (p Passenger) Charge(amount float64) {
if p.HasValidTicket{
return p // We already charged this Passenger.
}
fmt.Printf("Passenger with SSN %s: charged %.2f of arbitrary money\n",p.SSN,amount)
p.HasValidTicket=true
return p}

// PriceCalculator is used by BusCompany to determine the ticket price for a Passenger.
// PriceCalculator returns the ticket price in the local currency.
type PriceCalculator func(p Passenger) float64

Code snippet 24

Note how we don’t pass chargeFn directly to Passenger: it’s not Passenger’s responsibility to know any details about how a BusCompany handles ticket pricing, it’s sufficient that they know how to be charged a certain amount of money. But at this point, another question presents itself: who is responsible for passing chargeFn to Board?

BusCompany might offer these two policies.

// WorkdayPricing charges EUR 6 for regular Passengers
// and EUR 4.5 for seniors during workdays.
func WorkdayPricing(p Passenger) float64 {
if p.IsSenior() {
return 4.5
}
return 6.0
}

// WeekendPricing charges EUR 5 for regular Passengers
// and EUR 3.5 for seniors during weekends.
func WeekendPricing(p Passenger) float64 {
if p.IsSenior() {
return 3.5
}
return 5.0
}

Code snippet 25

It’s then up to the BusCompany to supply each Bus with the correct policy for the day.

// BusCompany represents the bus company responsible for the Bus service.
// BusCompany determines price policies.
type BusCompany string

// GetPricing returns a price calculator based on the pricing policy of the day.
func (b BusCompany) GetPricing() PriceCalculator {
wd := time.Now().Weekday()
if wd == time.Saturday || wd == time.Sunday {
return WeekendPricing
}
return WorkdayPricing
}

Code snippet 26

Now that we have a BusCompany that can supply prices - and two pricing strategies - we can refactor Bus.NotifyBusArrival to use the new Board method.

// NotifyBusArrival is called by Bus upon arrival.
func (b *BusStop) NotifyBusArrival(bus *Bus) {
for _, p := range b.prospects {
if bus.StopsAt(p.Destination) {
pas := p.ToPassenger()
bus.Board(pas, bus.Company.GetPricing()(pas))
}
}
}

Code snippet 27

To make this work, we just need to know if the Passenger is senior or not.

// SeniorAge is the minimum age from which a Passenger is considered
// a senior to the BusCompany.
const SeniorAge = 65

// IsSenior returns true if the Passenger is a senior, and false otherwise.
// IsSenior detects age by extracting the last two digits from the SSN and
// treating them like an age.
func (p Passenger) IsSenior() bool {
age,err:=strconv.ParseInt(p.SSN[len(p.SSN)-2:],10,8)
if err != nil {
panic("invalid SSN: " + p.SSN)
}
return age >= SeniorAge
}

Code snippet 28

We might have tied SeniorAge to BusCompany so it can vary with each company’s policy, but let’s just say that it’s a national law and therefore equal for all. In that case, using a const is fine. Also, just to keep it simple, we’ll use the last two digits of the SSN as the age and just panic if the age extraction fails. In a real program, we would propagate the error or check for valid SSN’s at the package boundaries so we don’t have to check it each and every time.

Going back to the main function for a second, we’ll immediately notice that these changes have made Betty a senior.

john := busservice.Prospect{
SSN:         "12345612-22",
Destination: &s2,
}
betty := busservice.Prospect{
SSN:         "11223322-67",
Destination: &s3,
}

Code snippet 29

We can now run the program and verify that Betty is indeed charged a lower ticket price for seniors (in this case the weekend price). Output below.

Starting simulation
Express Line: starting
Express Line: arriving at "Downtown"
Passenger with SSN 12345612-22: charged 5.00 of arbitrary money
Express Line: boarded passenger with SSN "12345612-22"
Passenger with SSN 11223322-67: charged 3.50 of arbitrary money
Express Line: boarded passenger with SSN "11223322-67"
Passenger with SSN "12345612-22" is heading to "The University"
Passenger with SSN "11223322-67" is heading to "The Village"
Express Line: carrying 2 passengers: heading for next stop
Express Line: arriving at "The University"
Express Line: unboarded passenger with SSN "12345612-22"
Passenger with SSN "11223322-67" is heading to "The Village"
Express Line: reached the end of the line, everybody out
Express Line: unboarded passenger with SSN "11223322-67"
Simulation done

Code snippet 30

The Strategy Pattern allowed us to keep Bus focused on charging the Passenger for the ride, rather than the technicalities of the implementation: whether or not it’s a weekday and to what degree BusCompany decides to let the Passenger’s characteristics affect the pricing. The method Bus.Board receives a simple PriceCalculator function and leaves it up to the BusCompany to analyze the situation and provide the correct pricing policy.

## Conclusion

Over the course of this bus tour, we’ve applied the Visitor Pattern to avoid exposing an internal data structure (Bus.Passengers) to other packages. We then went on to abstract the same data structure using the Facade Pattern, which allows us to write convenience methods that operate easily on a collection of passengers, which we demonstrated by implementing a solution for getting a passenger manifest.

Next, we started visiting different bus stops while boarding and unboarding passengers, which we achieved by implementing an event-driven notification system using the Observer Pattern. This allows us to keep responsibilities where they belong as opposed to having a know-it-all algorithm that ties into everything else.

After having verified that our algorithm works, we then applied the Strategy Pattern in order to charge passengers different ticket prices without creating a dependency on a specific implementation, and while keeping the responsibilities of the calculation details out of the details of how a bus operates.

Finally, we ran the finished simulation and took a couple of passengers around the city.

I hope you enjoyed reading, and maybe even learned something. The entire tour code is available in my GitHub repository.