grep Regular Expression

1.1) grep: is a text Search tool. The so-called metacharacters is not meant literal meaning, meta-character expression control or wildcard functions

2) Fgep:fast, does not support regular expressions, when literal representation.

"Grep"

1. Basic regular expression meta-characters:

. : Matches a single character.

[]: matches any single character within the specified range.

such as [0-9] = = = [[:d igit:]], [a-z] = = = [[: Lower:]], [a-z] = = = [[: Upper:]], [^]: Reverse

[[: Space:]]: space, [[:p UNCT:]]: special characters, [[: Alpha:]]: Uppercase and lowercase [[: Alnum:]]: Letters or numbers

2. Number of times match metacharacters: Specifies the number of occurrences of the preceding character

①*: Any length, the characters in front of him can appear any time

②\? : A single character appears 0 or one time

③\{m\}: Exact match appears m times

④\{m,n\}: Appears at least m times, up to N times

3. Position anchoring

Beginning: ^ Line end: $ word Left: \< word right:\>

A string of words that do not contain the characters of a continuous character of special characters

4. Grouping \ (* * * \) Once grouped, the group is considered an atomic unit

\#: Refers to the content that the # # brackets match to, not the pattern itself

5. Command options

-V: the inverse selection

-O: Only matching strings are displayed, not the lines where the strings are located

-I: Ignore case

-e: extending regular expressions

-A: Displays the following line

-B: Display the line above

-C: Display context

In the extended regular expression are also:

+: match at least once

grep Regular Expression