Grep--linux Text Processing One of the Three Musketeers

Linux Text Processing Three musketeers: grep sed awk

Grep:global search Regular expression and Print out of the line.

Function: A text Search tool that matches the target text against the user-specified filter criteria and prints out qualifying rows

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

Use: grep [OPTIONS] PATTEN [FILE ...]

OPTIONS:

--colour=auto: Coloring a match to a string after highlighting

-i:ignorecase, ignoring the case of characters;

-O: Displays only the matching string;

-V: Matched rows are not displayed, displaying rows that cannot be matched

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

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

-a #:after displays the following # lines of matching rows

-B #: Before displays the first # lines of matching rows

-C #: Context, show 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 IGLT:] [: Alpha:] [: Upper:] [: Lower:] [: Alnum:] [:p UNCT:] [: Space:]

Number of matches:

*: matches the preceding character any number of times, 0, 1, multiple times

. *: Matches any character of any length

\?: matches its preceding character 0 or 1 times,

\+: Matches its preceding character at least once;

\{m\}: Matches its 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:

^: denotes the beginning of a character following a symbol

$: Indicates the end of a character preceded by a symbol

\< or \b: The first anchor of the word to the left of the word pattern

\> or \b: ending anchor for the rightmost side of the word pattern

\<patten\>: Match full word PATTEN

Group and application:

\ (\): Bind one or more characters together and treat them as a whole;

Note: The contents of the pattern matching in the grouping brackets are automatically recorded in the internal variables by the regular expression engine, these variables are:

\1: The pattern from the left side, the first opening parenthesis, and the matching closing parenthesis, matches the character of the pattern;

\2: The pattern from the left side, the second opening parenthesis, and the matching closing parenthesis, matches the character of the pattern;

\3: ...

...

egrep:

An extended regular expression implementation is similar to the grep text filtering feature; grep-e

Egrep [OPTION] PATTEN [FILE]

Options:

-i,-o,-v,-q,-a,-b,-c

-G: Support for basic regular expressions

Extend the metacharacters of regular expressions:

Character Matching:

.: matches any single character;

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

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

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

Number of matches:

*: Any time

?: 0 Times or 1 times

+:1 Times or more

{m}:m times

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

{0,n}, {m,}

Location anchoring:

^: denotes the beginning of a character following a symbol

$: Indicates the end of a character preceded by a symbol

\< or \b: The first anchor of the word to the left of the word pattern

\> or \b: ending anchor for the rightmost side of the word pattern

\<patten\>: Match full word PATTEN

Group and application:

(): Bind one or more characters together and treat them as a whole;

Note: The contents of the pattern in the grouping brackets are automatically recorded in the internal variables by the regular expression engine

Or:

A|b:a or B

C|cat:c or cat

(c|c) At:cat or cat

Grep--linux Text Processing One of the Three Musketeers