sed

Stream Editor. Fast and simple using standard GNU Regular Expression Syntax.

A nice fact is that Vim uses very similar syntax for searching and replacing.

Tips

• Basic usage example:

echo hello world | sed 's/hello/good morning/' 

Output:

good morning world

• Replace text in multiple files via grep:

grep -rl "string_to_match_in_files" somedirectory/ | xargs sed -i 's|string1|string2|g'

This can be further refined by piping from find aswell.

Links

• Possibly the most useful - A full description : http://www.grymoire.com/Unix/Sed.html