Grep, egrep and their corresponding regular expressions and usage

Grep: grep,egrep,fgrep, text search tool, fuzzy search for given text based on PATTERN. GREP works in greedy mode by default.

Grep:

Grep [OPTIONS] PATTERN [FILE...]

PATTERN: the filter condition consists of regular expression metacharacters and text characters that have no special meaning.

Regular expression metacharacters:

Will be interpreted as a special meaning by the regular expression engine. Regular expression engine for the pcre--perl language.

Basic regular expression: BRE

Extended regular expression: ERE

Grep only supports basic regular expressions by default

Egrep only supports extended regular expressions by default.

Fgrep does not turn on the regular expression engine by default

Text characters:

Those characters that have only one-sided meaning

Common options:

-I,-- ignore-case ignores the case of text characters

-v,-- invert-match match in reverse, and the final result is the row that PATTREN cannot match

-c,-- count counts all rows that match PATTERN

-o,-- only-matching turns off greedy mode and displays only what PATTERN can match

-Q,-- quiet,-- silent does not output any matching results

-- color [= WHEN],-- colour [= WHEN] displays the contents of the matching PATTREN in a special color

-E,-- extended-regexp extended regular expression grep-E is equivalent to egrep

-F,-- fixed-strings,-- fixed-regexp is equivalent to fgrep

-G,-- basic-regexp basic regular expression, egrep-G is equivalent to grep

-P,-- perl-regexp uses the PCRE engine

-A NUM,-- after-context=NUM displays the rows that match the PATTERN and the NUM lines that follow them

-B NUM-- before-context=NUM

PATTERN

Regular expression metacharacters:

Basic regular expression metacharacters:

GLOBBING- simplified version of regular expression: []? *

Character matching:

.: match any single character

[]: matches any single character in the specified range

[^]: matches any single character outside the specified range

All of the following character sets can be placed in [] to match a single character

[: lower:]

[: upper:]

[: alpha:]

[: digit:]

[: space:] Spac

[: alnum:]

[: punct:]

[: blank:]

[: xdigit:]: all hexadecimal numbers

Amurz: all lowercase letters

Amurz: all capital letters

0-9: all decimal numbers

Number of times matching: the number of times that a character before this class can appear

*: the character in front of it can appear any number of times (0, 1 or more times)

The character in front of it is optional (0 times or once)

\ +: the character preceding it appears at least once (1 or more times)

\ {m\}: the character before it must appear m times

\ {mdirection n\}: at least m times and at most n times (m)