grep cheat sheet

Grep is a command-line tool that allows you to search for specific patterns or words in a file or group of files. It is commonly used by programmers, system administrators, and analysts to search for specific patterns in logs, configuration files, and other types of data.

To use grep, you specify the pattern you want to search for and the file or files you want to search in. Grep will then output all lines that contain the pattern.

Here is a basic example of using grep to search for the word “error” in a file called file.txt:

grep error file.txt

This will show all lines in file.txt that contain the word “error”.

Grep has many options that allow you to customize the search, such as ignoring case, showing line numbers, and searching multiple files. You can also use regular expressions, which are a powerful way to specify complex patterns to search for.

Here is my grep cheat sheet to help you get started with using grep.

Option	Description	Example
-v	Invert the search, showing lines that do not match the pattern	grep -v error file.txt
-e	Specify multiple patterns to search for	grep -e error -e warning file.txt
-f	Specify a file containing patterns to search for or exclude	grep -f patterns.txt file.txt
-c	Count the number of lines that match the pattern	grep -c error file.txt
-i	Ignore case when searching	grep -i error file.txt
-n	Prefix each line of output with the line number	grep -n error file.txt
-l	Only show the names of files that contain a match	grep -l error *.log
-r	Recursively search subdirectories	grep -r error /var/log
-E	Interpret the pattern as an extended regular expression	grep -E '[0-9]*error' file.txt
-w	Only match whole words	grep -w error file.txt
-x	Only show lines that match the pattern exactly	grep -x error file.txt

Here is an explanation of each option:

• -v: Inverts the search, showing lines that do not match the pattern. For example, grep -v error file.txt will show all lines in file.txt that do not contain the word “error”.
• -e: Allows you to specify multiple patterns to search for. For example, grep -e error -e warning file.txt will show all lines in file.txt that contain either the word “error” or the word “warning”.
• -f: Allows you to specify a file containing patterns to search for or exclude. For example, grep -f patterns.txt file.txt will show all lines in file.txt that contain any of the patterns in patterns.txt.
• -c: Counts the number of lines that match the pattern. For example, grep -c error file.txt will show the number of lines in file.txt that contain the word “error”.
• -i: Ignores case when searching. For example, grep -i error file.txt will show all lines in file.txt that contain the word “error”, regardless of whether it is capitalized or not.
• -n: Prefixes each line of output with the line number. For example, grep -n error file.txt will show all lines in file.txt that contain the word “error”, along with the line number.
• -l: Only shows the names of files that contain a match. For example, grep -l error *.log will show the names of all .log files that contain the word “error”.

• -r: Recursively searches subdirectories. For example, grep -r error /var/log will search for the word “error” in all files under the /var/log directory, including subdirectories.
• -E: Interprets the pattern as an extended regular expression. Regular expressions, or regex, are a powerful way to specify complex patterns to search for. Extended regular expressions add additional features, such as the ability to match multiple characters with a single expression. For example, grep -E '[0-9]*error' file.txt will show all lines in file.txt that contain a number followed by the word “error”.
• -w: Only matches whole words. For example, grep -w error file.txt will show all lines in file.txt that contain the word “error” as a whole word, but will not match lines that contain the word “error” as a part of another word.
• -x: Only shows lines that match the pattern exactly. For example, grep -x error file.txt will show all lines in file.txt that contain the word “error” and nothing else.

I hope this grep cheatsheet is helpful!