freeCodeCamp/guide/english/bash/bash-grep/index.md

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Bash grep

Bash command: grep

The grep command is used to find matching text in input file(s). Default output lists lines from the input file(s) which contain a match to the provided pattern. Options may be used to alter matching behavior or to provide a different output scheme.

Usage

grep [options] [pattern] [file_names]

Common options:

• -i, Ignore case when mathing the provided pattern
• -v, Show results which do not match the provided pattern.
• -l, Instead of outputting matching lines, output the file paths which contain matching text.
• -r, Search all files in the provided directories. Directory name(s) or path(s) is used in place of the file name(s) (Search defaults to the current working directory if none is provided)
• -c, Output a count of the matching lines.
• -E, Use extended regular expressions to define the pattern to be matched. The command alias egrep is the same as grep -E

Examples:

Search a server log file for lines containing the text "ERROR":

grep ERROR server.log

Using a pipe to combine commands, list files and folders in the current working directory that contain the text "code":

ls | grep code

Search for IP 127.0.0.1 in the /etc/hosts file

grep "127.0.0.1" /etc/hosts

Search for oom (out of memory) in /var/log/messages

grep -i oom /var/log/messages

More Information

• Bash Guide for Beginners, Examples using grep
• Wikipedia