Find (Unix)
# Find (Unix)

In Unix-like and some other operating systems, find is a command-line utility that locates files based on some user-specified criteria and either prints the pathname of each matched object or, if another action is requested, performs that action on each matched object.

It initiates a search from a desired starting location and then recursively traverses the nodes (directories) of a hierarchical structure (typically a tree). find can traverse and search through different file systems of partitions belonging to one or more storage devices mounted under the starting directory.

The possible search criteria include a pattern to match against the filename or a time range to match against the modification time or access time of the file. By default, find returns a list of all files below the current working directory, although users can limit the search to any desired maximum number of levels under the starting directory.

The related locate programs use a database of indexed files obtained through find (updated at regular intervals, typically by cron job) to provide a faster method of searching the entire file system for files by name.

## History

find appeared in Version 5 Unix as part of the Programmer's Workbench project, and was written by Dick Haight alongside cpio, which were designed to be used together.

The GNU find implementation was originally written by Eric Decker. It was later enhanced by David MacKenzie, Jay Plett, and Tim Wood.

The find command has also been ported to the IBM i operating system.

## Find syntax

The two options control how the find command should treat symbolic links. The default behaviour is never to follow symbolic links. The -L flag will cause the find command to follow symbolic links. The -H flag will only follow symbolic links while processing the command line arguments. These flags are specified in the POSIX standard for find. A common extension is the -P flag, for explicitly disabling symlink following.

At least one path must precede the expression. find is capable of interpreting wildcards internally and commands must be quoted carefully in order to control shell globbing.

Expression elements are separated by the command-line argument boundary, usually represented as whitespace in shell syntax. They are evaluated from left to right. They can contain logical elements such as AND (-and or -a) and OR (-or or -o) as well as predicates (filters and actions).

GNU find has a large number of additional features not specified by POSIX.

### Predicates

Commonly-used primaries include:

* -name pattern: tests whether the file name matches the shell-glob pattern given.
* -type type: tests whether the file is a given type. Unix file types accepted include:
   * b: block device (buffered);
   * c: character device (unbuffered);
   * d: directory;
   * f: regular file;
   * l: symbolic link;
   * p: named pipe;
   * s: socket;
   * D: door.
* -print: always returns true; prints the name of the current file plus a newline to the stdout.
* -print0: always returns true; prints the name of the current file plus a null character to the stdout. Not required by POSIX.
* -exec program [arguments...] ;: runs program with the given arguments, and returns true if its exit status was 0, false otherwise. If program, or an argument is, it will be replace by the current path (if program is, find will try to run the current path as an executable). POSIX doesn't specify what should happen if multiple are specified. Most implementations will replace all with the current path, but that is not standard behavior.
* -exec program [arguments...] +: always returns true; run program with the given arguments, followed by as many paths as possible (multiple commands will be run if the maximum command-line size is exceeded, like for xargs).
* -ok program [arguments...] ;: for every path, prompts the user for confirmation; if the user confirms (typically by entering y or yes), it behaves like -exec program [arguments...] ;, otherwise the command is not run for the current path, and false is returned.

If the expression uses none of -print0, -print, -exec, or -ok, find defaults to performing -print if the conditions test as true.

### Operators

Operators can be used to enhance the expressions of the find command. Operators are listed in order of decreasing precedence:

* ( expr ): forces precedence;
* ! expr: true if expr is false;
* expr1 expr2 (or expr1 -a expr2: AND. expr2 is not evaluated if expr1 is false;
* expr1 -o expr2: OR. expr2 is not evaluated if expr1 is true.

This command searches the current working directory tree for files whose names start with fileA_ or fileB_. We quote the fileA_* so that the shell does not expand it.

This command searches the current working directory tree except the subdirectory tree ".svn" for files whose name is "foo.cpp". We quote the ! so that it's not interpreted by the shell as the history substitution character.

## POSIX protection from infinite output

Real-world file systems often contain looped structures created through the use of hard or soft links. The POSIX standard requires that

   The find utility shall detect infinite loops; that is, entering a previously visited directory that is an ancestor of the last file encountered. When it detects an infinite loop, find shall write a diagnostic message to standard error and shall either recover its position in the hierarchy or terminate.

## Examples

### From the current working directory

This searches the current working directory tree for files whose names start with my. The single quotes avoid the shell expansion—without them the shell would replace my* with the list of files whose names begin with my in the current working directory. In newer versions of the program, the directory may be omitted, and it will imply the current working directory.

### Regular files only

This limits the results of the above search to only regular files, therefore excluding directories, special files, symbolic links, etc. my* is enclosed in single quotes (apostrophes) as otherwise the shell would replace it with the list of files in the current working directory starting with my…

### Commands

The previous examples created listings of results because, by default, find executes the -print action. (Note that early versions of the find command had no default action at all; therefore the resulting list of files would be discarded, to the bewilderment of users.)

This prints extended file information.

### Search all directories

This searches every directory for a regular file whose name is myfile and prints it to the screen. It is generally not a good idea to look for files this way. This can take a considerable amount of time, so it is best to specify the directory more precisely. Some operating systems may mount dynamic file systems that are not congenial to find. More complex filenames including characters special to the shell may need to be enclosed in single quotes.

### Search all but one subdirectory tree

This searches every directory except the subdirectory tree excluded_path (full path including the leading /) that is pruned by the -prune action, for a regular file whose name is myfile.

### Specify a directory

This searches the /home/weedly directory tree for regular files named myfile. You should always specify the directory to the deepest level you can remember.

### Search several directories

This searches the local subdirectory tree of the current working directory and the /tmp directory tree for directories named mydir.

### Ignore errors

If you're doing this as a user other than root, you might want to ignore permission denied (and any other) errors. Since errors are printed to stderr, they can be suppressed by redirecting the output to /dev/null. The following example shows how to do this in the bash shell:

If you are a csh or tcsh user, you cannot redirect stderr without redirecting stdout as well. You can use sh to run the find command to get around this:

An alternate method when using csh or tcsh is to pipe the output from stdout and stderr into a grep command. This example shows how to suppress lines that contain permission denied errors.

### Find any one of differently named files

The -ls operator prints extended information, and the example finds any regular file whose name ends with either 'jsp' or 'java'. Note that the parentheses are required. In many shells the parentheses must be escaped with a backslash (\( and \)) to prevent them from being interpreted as special shell characters. The -ls operator is not available on all versions of find.

### Execute an action

This command changes the permissions of all regular files whose names end with .mp3 in the directory tree /var/ftp/mp3. The action is carried out by specifying the statement -exec chmod 644 \; in the command. For every regular file whose name ends in .mp3, the command chmod 644 is executed replacing with the name of the file. The semicolon (backslashed to avoid the shell interpreting it as a command separator) indicates the end of the command. Permission 644, usually shown as rw-r--r--, gives the file owner full permission to read and write the file, while other users have read-only access. In some shells, the must be quoted. The trailing ";" is customarily quoted with a leading "\", but could just as effectively be enclosed in single quotes.

Note that the command itself should not be quoted; otherwise you get error messages like

which means that find is trying to run a file called 'echo "mv ./3bfn rel071204"' and failing.

If you will be executing over many results, it is more efficient to use a variant of the exec primary that collects filenames up to ARG_MAX and then executes COMMAND with a list of filenames.

This will ensure that filenames with whitespaces are passed to the executed COMMAND without being split up by the shell.

### Delete files and directories

The -delete action is a GNU extension, and using it turns on -depth. So, if you are testing a find command with -print instead of -delete in order to figure out what will happen before going for it, you need to use -depth -print.

Delete empty files and print the names (note that -empty is a vendor unique extension from GNU find that may not be available in all find implementations):

Delete empty regular files:

Delete empty directories:

Delete empty files named 'bad':

Warning. — The -delete action should be used with conditions such as -empty or -name:

### Search for a string

This command will search all files from the /tmp directory tree for a string:

The /dev/null argument is used to show the name of the file before the text that is found. Without it, only the text found is printed. (Alternatively, some versions of grep support a -H flag that forces the file name to be printed.) GNU grep can be used on its own to perform this task:

Example of search for "LOG" in jsmith's home directory tree:

Example of search for the string "ERROR" in all XML files in the current working directory tree:

The double quotes (" ") surrounding the search string and single quotes (' ') surrounding the braces are optional in this example, but needed to allow spaces and some other special characters in the string. Note with more complex text (notably in most popular shells descended from `sh` and `csh`) single quotes are often the easier choice, since double quotes do not prevent all special interpretation. Quoting filenames which have English contractions demonstrates how this can get rather complicated, since a string with an apostrophe in it is easier to protect with double quotes:

### Search in case insensitive mode

Note that -iname is not in the standard and may not be supported by all implementations.

If the -iname switch is not supported on your system then workaround techniques may be possible such as:

### Search files by size

Searching files whose size is between 100 kilobytes and 500 kilobytes:

Searching empty files:

Searching non-empty files:

### Search files by name and size

This command will search the /usr/src directory tree. All files that are of the form '*,v' and '.*,v' are excluded. Important arguments to note are in the tooltip that is displayed on mouse-over.

The units should be one of [bckw], 'b' means 512-byte blocks, 'c' means byte, 'k' means kilobytes and 'w' means 2-byte words. The size does not count indirect blocks, but it does count blocks in sparse files that are not actually allocated.

### Searching files by time

Date ranges can be used to, for example, list files changed since a backup.

* -mtime : modification time
* -ctime : inode change time
* -atime : access time

Files modified a relative number of days ago:

* +[number] = At least this many days ago.
* -[number] = Less than so many days ago.
* [number] = Exactly this many days ago.
* Optionally add -daystart to measure time from the beginning of a day (0 o'clock) rather than the last 24 hours.

Example to find all text files in the document folder modified since a week (meaning 7 days):

Files modified before or after an absolute date and time:

* -newermt YYYY-MM-DD: Last modified after date
* -not -newermt YYYY-MM-DD: Last modified before date

Example to find all text files last edited in February 2017:

* -newer [file]: More recently modified than specified file.
   * -cnewer: Same with inode change time.
   * -anewer: Same with access time.
   * Also prependable with -not for inverse results or range.

List all text files edited more recently than "document.txt":

## Related utilities

* locate is a Unix search tool that searches a prebuilt database of files instead of directory trees of a file system. This is faster than find but less accurate because the database may not be up-to-date.
* grep is a command-line utility for searching plain-text data sets for lines matching a regular expression and by default reporting matching lines on standard output.
* tree is a command-line utility that recursively lists files found in a directory tree, indenting the filenames according to their position in the file hierarchy.
* GNU Find Utilities (also known as findutils) is a GNU package which contains implementations of the tools find and xargs.
* BusyBox is a utility that provides several stripped-down Unix tools in a single executable file, intended for embedded operating systems with very limited resources. It also provides a version of find.
* dir has the /s option that recursively searches for files or directories.
* Plan 9 from Bell Labs uses two utilities to replace find: a walk that only walks the tree and prints the names and a sor that only filters (like grep) by evaluating expressions in the form of a shell script. Arbitrary filters can be used via pipes. The commands are not part of Plan 9 from User Space, so Google's Benjamin Barenblat has a ported version to POSIX systems available through GitHub.
* fd is a simple alternative to find written in the Rust programming language.
