Recipe: Basic regular expression primer

Grep Syntax
===========
user@host:~$ grep match_pattern filename


user@host:~$ grep "match_pattern" filename


Stdin
=====
user@host:~$ echo -e "this is a word\nnext line" | grep word

Multiple Files Input
====================
user@host:~ $ grep "match_text" file1 file2 file3 ...

Colouring in grep
=================
user@host:~ $ grep word filename --color auto


Regular expression
==================
user@host:~ $ grep -E "[a-z]+"

Regular expression with egrep
=============================
user@host:~ $ egrep "[a-z]+"


Print only matching portion
===========================
user@host:~ $ echo this is a line. | grep -o -E "[a-z]+\."
line.

Print only matching portion with egrep
======================================
user@host:~ $ echo this is a line. | egrep -o "[a-z]+\."
line.

Invert matching
===============
user@host:~ $ grep -v  match_pattern file


Counting matches
================
user@host:~ $ grep -c "text" filename


user@host:~ $ echo -e "1 2 3 4\nhello\n5 6" | egrep  -c "[0-9]"
2

user@host:~ $ echo -e "1 2 3 4\nhello\n5 6" | egrep  -o "[0-9]" | wc -l
6


user@host:~ $ cat sample1.txt
gnu is not unix
linux is fun
bash is art


user@host:~ $ cat sample2.txt
planet linux


user@host:~ $ grep linux -n sample1.txt
2:linux is fun

user@host:~ $ cat sample1.txt | grep linux -n
2:linux is fun


user@host:~ $ grep linux -n sample1.txt sample2.txt
sample1.txt:2:linux is fun
sample2.txt:2:planet linux


user@host:~ $ echo gnu is not unix | grep -b -o "not"
7:not


user@host:~ $ grep -l linux sample1.txt sample2.txt
sample1.txt
sample2.txt


user@host:~ $ grep "text" . -R -n


user@host:~ $ cd src_dir
user@host:~ $ grep "test_function()" . -R -n
./miscutils/test.c:16:test_function();


user@host:~ $ echo hello world | grep -o "HELLO"
hello



user@host:~ $ grep -e "pattern1" -e "pattern
 

user@host:~ $ echo this is a line of text | grep -e "this" -e "line" -o
this
line


user@host:~ $ grep -f pattern_file source_filename



user@host:~ $ cat pat_file
hello


user@host:~ $ echo hello this is cool | grep -f pattern 
hello this is cool


user@host:~ $ grep "main()" . -r  --include *.{c,cpp}


user@host:~ $ grep "main()"  . -r –-exclude "README" 



Scripts
=======

silent_grep.sh