Metacharacters of egrep

Metacharacters of egrep

metacharacters in use

Reading Notes


👣 #regex

Summary of the egrep metacharacters1:

Metacharacter Matches
.dotMatches any one character
[. . .]character classMatches any one character listed
[^. . .]negated character classMatches any one character not listed
\charescaped characterWhen char is a metacharacter, or the escaped combination is not otherwise special, matches the literal char
?questionOne allowed, but it is optional
*starAny number allowed, but all are optional
+plusAt least one required; additional are optional
{min, max}specified rangeMin required, max allowed
^caretMatches the position at the start of the line
$dollarMatches the position at the end of the line
\<word boundaryMatches the position at the start of a word
\>word boundaryMatches the position at the end of a word
|alternationMatches either expression it separates
(. . .)parenthesesLimits scope of alternation, provides grouping for the quantifiers, and “captures” for backreferences
\1, \2, ...backreferenceMatches text previously matched within first, second, etc., set of parentheses

not supported by all versions of egrep

There’re three types of escaped items:

  1. The pairing of \ and a metacharacter is a metasequence to match the literal character (for example, \* matches a literal asterisk).
  2. The pairing of \ and selected non-metacharacters becomes a metasequence with an implementation-defined meaning (for example, \< often means “start of word”).
  3. The pairing of \ and any other character defaults to simply matching the charater literal (that is, the backslash is ignored).
  1. Friedl, Jeffrey E. F. Mastering Regular Expressions. 3rd ed. Sebastapol, CA: O’Reilly, 2006. 

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