dmesg | grep -i 'usb'  here the dmesg command is piped through grep to extract any patterned data matching 'usb'
grep is a unix/linux utility that searches the named input file/s for lines containing a match to the given pattern
"dmesg | grep -i 'usb'  here the dmesg command is piped through grep to extract any patterned data matching 'usb'" What is the definition of "grep"?