Open Source Research and Development » grep FAQ

how do i grep on a term with a $ in it such as $foo? i tried enclosing it in quotes but that doesn’t help

admin — Mon, 16 Feb 2009 04:57:33 +0000

Enclose the $ in square brackets [ .. ], that is, specify the special character as a character class. For example,

grep ‘[$]foo’ file.txt

if I wanted to match ‘foo13245′, can I use grep ‘foo[\d]*’?

admin — Wed, 07 Jan 2009 12:30:39 +0000

Nope, \d has no meaning (unless using -P for PCRE). You need [[:digit:]] instead; i.e.,

grep 'foo[[:digit:]]*'

How can i search for files which contain string A but not string B ?

admin — Tue, 06 Jan 2009 12:00:36 +0000

Pipe the output of grep through grep -v. For example:
grep 'A' file | grep -v 'B'

Why grep ‘foo|bar’ file doesn’t work?

admin — Mon, 05 Jan 2009 13:00:06 +0000

The bar | has no special meaning in BRE (basic regular expressions). Use extended regular expressions (ERE) such as:

grep -E 'foo|bar' file

egrep 'foo|bar' file

In GNU grep, you can also force the spcial meaning of | by escaping it. E.g.,

grep 'foo\|bar' file

Is grep an acronym? Does it mean GNU Regular Expression P?

admin — Sun, 04 Jan 2009 20:32:03 +0000

grep originated from ed command: g/re/p where re is a regular expression, g stands for globally, and p stands for print. So one could say grep is an acronym of “Global Regular Expression Print“.