Regular expressions (regexp)

Summary

The commands that use basic and extended regular expressions are as follows:
Basic
ed, expr, grep, sed
Extended
awk, grep with -E option, sed with the -E option.
Table 1 summarizes the features that apply to the applicable shell commands.
Table 1. Features that apply to different shells (regexp)
Notation awk ed grep -E expr sed
. Yes Yes Yes Yes Yes
^ Yes Yes Yes No Yes
$ Yes Yes Yes Yes Yes
[...] Yes Yes Yes Yes Yes
[::] Yes Yes Yes Yes Yes
re* Yes Yes Yes Yes Yes
re+ Yes No Yes No No
re? Yes No Yes No No
re|re Yes No Yes No No
\d Yes Yes Yes Yes Yes
(...) Yes No Yes No No
\(...\) No Yes No Yes Yes
\< No No No No No
\> No No No No No
\{ \} Yes No Yes No Yes

Examples

The following patterns are given as illustrations, along with descriptions of what they match:
abc
Matches any line of text containing the three letters abc in that order.
a.c
Matches any string beginning with the letter a, followed by any character, followed by the letter c.
^.$
Matches any line containing exactly one character (the newline is not counted).
a(b*|c*)d
Matches any string beginning with a letter a, followed by either zero or more of the letter b, or zero or more of the letter c, followed by the letter d.
.* [a-z]+ .*
Matches any line containing a word, consisting of lowercase alphabetic characters, delimited by at least one space on each side.
(morty).*\1
 
morty.*morty
These expressions both match lines containing at least two occurrences of the string morty.
[[:space:][:alnum:]]
Matches any character that is either a white space character or alphanumeric.