grep, Egrep

One, grep global search regular expression, and print out the row  

Function: Text Search tool, according to user-specified "mode (filter)" to match the target text line by row to check; print matching lines;

Pattern: The filter condition written by metacharacters and text characters of regular expressions;

The regular expression engine;

grep [OPTIONS] PATTERN [FILE ...]

grep [OPTIONS] [-E PATTERN |-f file] [FILE ...]

OPTIONS:

--color=auto: Color The matching text to highlight;

-i:ignorecase, ignoring the case of characters;

-O: Displays only the string that matches to itself;

-V,--invert-match: Displays the rows that cannot be matched by the pattern;

-E: Supports the use of extended regular expression metacharacters;

-Q,--quiet,--silent: Silent mode, that is, do not output any information;

-A #:after, after # line

-B #:before, front # line

-c #:context, front and back # lines

Basic regular Expression meta-characters:

Character Matching:

. : matches any single character;

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

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

[:d Igit:], [: Lower:], [: Upper:], [: Alpha:], [: Alnum:], [:p UNCT:], [: Space:]

Number of matches: used to limit the number of occurrences of the preceding character after the character to specify the number of occurrences, and the default work is in greedy mode;

*: Matches its preceding character any time, 0, 1, multiple times;

. *: Matches any character of any length

\?: matches the preceding character 0 or 1 times, that is, the preceding character is optional;

\+: Matches the preceding character 1 or more times, i.e. the character of its face must appear at least 1 times;

\{m\}: Matches the preceding character m times;

\{m,n\}: Matches its preceding character at least m times, up to n times;

\{0,n\}: Up to n times

\{m,\}: At least m times

Location anchoring:

^: Anchor at the beginning of the line, for the leftmost mode;

$: End of line anchoring; for the rightmost side of the pattern;

^pattern$: Used for PATTERN to match whole line;

^$: blank line;

^[[:space:]]*$: A blank line or a line containing white space characters;

Word: A continuous character (string) consisting of a non-special character is called a word;

\< or \b: The first anchor of the word, used for the left side of the word pattern;

\> or \b: The ending anchor for the right side of the word pattern;

\<pattern\>: matches complete words;

Second, Egrep an extended regular expression implementation is similar to the grep text filtering feature; Grep-e

Egrep [OPTIONS] PATTERN [FILE ...]

Options:

-I,-O,-V,-Q,-A,-B,-C

-G: Support for basic regular expressions

Extend the metacharacters of regular expressions:

Character Matching:

.: Any single character

[]: Any single character within the specified range

[^]: Any single character outside the specified range

Number of matches:

*: Any time, 0,1 or multiple times;

?: 0 or 1 times, before the characters are optional;

+: Its preceding character at least 1 times;

{m}: its preceding character m times;

{M,n}: At least m times, up to n times;

{0,n}

{m,}

Position anchoring

^: Anchor at the beginning of the line;

$: End of line anchoring;

\< \b: The first anchor of the word;

\> \b: the final anchor;

Grouping and referencing:

(): grouping; the character that the pattern in parentheses matches to is recorded hermetical the internal variables of the expression engine;

Back reference: \1, \2, ...

Or:

A|b:a or B;

C|cat:c or Cat

(c| C) At:cat or cat

This article from "Everything from scratch, do not forget beginner's mind." "Blog, be sure to keep this provenance http://liaodijin.blog.51cto.com/10988244/1730878

grep, Egrep