grep

Usage

grep <options> pattern <file...>

Pattern options

-F, --fixed-strings   # list of fixed strings

-G, --basic-regexp    # basic regular expression (default)

-E, --extended-regexp # extended regular expression

-P, --perl-regexp     # perl compatible regular expression

Output Options

-c, --count           # print the count of matching lines. suppresses normal output

    --color[=WHEN]    # applies color to the matches. WHEN is never, always, or auto

-m, --max-count=NUM   # stop reading after max count is reached

-o, --only-matching   # only print the matched part of a line

-q, --quiet, --silent

-s, --no-messages     # suppress error messages about nonexistent or unreadable files

Context Options

-B NUM, --before-context=NUM  # print NUM lines before a match

-A NUM, --after-context=NUM   # print NUM lines after a match

-C NUM, -NUM, --context=NUM   # print NUM lines before and after a match

Matching options

-e, --regexp=PATTERN

-f, --file=FILE

-i, --ignore-case

-v, --invert-match

-w, --word-regexp

-x, --line-regexp

Expressions

Basic Regular Expressions (BRE)

In BRE, these characters have a special meaning unless they are escaped with a backslash:

^ $ . * [ ] \

However, these characters do not have any special meaning unless they are escaped with a backslash:

? + { } | ( )

Extended Regular Expressions (ERE)

ERE gives all of these characters a special meaning unless they are escaped with a backslash:

^ $ . * + ? [ ] ( ) | { }

Examples

# Case insensitive: match any line in foo.txt

# that contains "bar"

grep -i bar foo.txt

#  match any line in bar.txt that contains

# either "foo" or "oof"

grep -E "foo|oof" bar.txt

# match anything that resembles a URL in

# foo.txt and only print out the match

grep -oE "https?:\/\/((\w+[_-]?)+\.?)+" foo.txt

# can also be used with pipes:

# match any line that contains "export" in

# .bash_profile, pipe to another grep that

# matches any of the first set of matches

# containing "PATH"

grep "export" .bash_profile | grep "PATH"

# follow the tail of server.log, pipe to grep

# and print out any line that contains "error"

# and include 5 lines of context

tail -f server.log | grep -iC 5 error