Grep is considered as one of the most useful commands on Unix-like operating systems. Here you’ll get basics that can be useful in your work.


Search the contents of files

grep [pattern] [file(s)]

Example:

> grep "import" *js


grep -i [pattern] [file(s)]

Example:

> grep -i "apiservice" *Service.js


Search recursevly inside directory

grep -r [pattern] [path]

Example:

-> Find “api” instances in the current directory recursevly

> grep -r "api" .


Find files by pattern

Sometimes there is a need to search inside files that could be selected by part of their name or extension.

find [path] -name [pattern]

Examples:

> find . -name "*Service.js"


Combining find and grep with xargs

xargs is a command used to build and execute commands. By default it’s using echo command.

Example:

-> Outputs the strings of find result

> find . -name "*js" | xargs

-> Outputs “todo” instances for files that ends with “Service.js”

> find . -name "*Service.js" | xargs grep "todo"

-> Same as previous command. You can use it, but using “find” is preferable from the side that we can test its output and be sure that pattern is ok

> grep -r --include="*Service.js" "todo" .


Search contents of git repository

git grep [pattern]

Example:

-> Searching “version” string in your project tracked files

`git grep version`


Grep mark up options:

-n : each output line is preceded by its relative line number in the file, starting at line 1

--color(-colour) : mark up the matching text with the expression stored in GREP_COLOR environment variable

Grep context options:

-A [num] : print “num” lines of trailing context after each match

-B [num] : print “num” lines of leading context before each match

-C [num] : print “num” lines of leading and trailing context surrounding each match. By default is 2 and is equivalent to -A 2 -B 2


Regular expressions

Basic:

. : any character

\ : escaping character (like \. for dot)

* : zero or more occurences of the regular expression

Extended:

To use extended regular expressions with grep, you’ll need to either escape them with backslashes or turn on extended regular expressions with the -E option.

? : matches zero or one occurence of the one-character regular expression

+ : matches one or more occurence of the one-character regular expression

| : separate alternatives

^ : matches the begining of a line

$ : matches the end of a line

[] : mathes any one character in that string

() : for grouping expressions


Find matches excluding a pattern

> find [path] -name [pattern] | grep -v [pattern]

-v : option for inverse