grep

grep linux command cheatsheet by Thamizhiniyan C S

Introduction

The grep filter searches a file for a particular pattern of characters, and displays all lines that contain that pattern. The pattern that is searched in the file is referred to as the regular expression.

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Important Flags

Flags	Description
-R	Does a recursive grep search for the files inside the folders(if found in the specified path for pattern search; else grep won't traverse directory for searching the pattern you specify)
-h	If you're grepping recursively in a directory, this flag disables the prefixing of filenames in the results.
-c	This flag won't list you the pattern only list an integer value, that how many times the pattern was found in the file/folder.
-i	Specifies grep to search for the PATTERN while IGNORING the case
-l	Will only list the filename instead of pattern found in it.
-n	It will list the lines with their line number in the file containing the pattern.
-v	This flag prints all the lines that are NOT containing the pattern
-E	This flag we already read above... will consider the PATTERN as a regular expression to find the matching strings.
-e	The official documentation says, it can be used to specify multiple patterns and if any string matches with the pattern(s) it will list it.

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Examples

Command	Description
grep "literal_string" filename	Search for the given string in a single file
grep "string" FILE_PATTERN	Checking for the given string in multiple files
grep -i "string" FILE	Case insensitive search
grep "REGEX" filename	Match regular expression in files
grep -iw "is" demo_file	Checking for full words, not for sub-strings using grep -w
grep -A "string" FILENAME	Display N lines after match
grep -B "string" FILENAME	Display N lines before match
grep -C "string" FILENAME	Display N lines around match
grep -r "ramesh" *	Searching in all files recursively using grep -r
grep -v "go" demo_text	Invert match using grep -v
grep -v -e "pattern" -e "pattern"	Display the lines which does not matches all the given pattern
grep -c "pattern" filename	Counting the number of matches using grep -c
grep -l this demo_*	Display only the file names which matches the given pattern using grep -l
grep -o "is.*line" demo_file	Show only the matched string
grep -o -b "pattern" file	Show the position of match in the line
grep -n "go" demo_text	Show line number while displaying the output using grep -n
grep -iRl [directory path/keyword]	Find files with a specific keyword