Lesson 6 of my Longco operation and maintenance staff (1)

Text processing three Musketeers

Grep Department: grep, egrep, fgrep, text search tools, located in the "PATTERN" to conduct fuzzy search for a given text.

Sed:tream EDitor, stream editor, line editor, text editing tool

Awk:gawk--GNU awd, text formatting tool, text report generator, editing language for text processing

Grep system: grep, egrep, fgrep

Grep:Global search REgular expression and Print out the line.

Use the addition expression to conduct a global search and display the matching lines

Format: grep [OPTIONS] PATTERN [FILE...]

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

Metacharacters of regular expressions: are interpreted as special meanings by the regular expression engine; the regular expression engine of the pcre--perl language; where regular expressions are divided into two categories:

1. Basic regular expression: BRE

2. 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 regular expressions by default.

Text characters: characters that have only the superficial meaning of the characters

Common options:

-imam: ignore the case of text characters

-vmam talk match: direction match; the final result is a row that PATTERN does not match

-cmam Mutual account: count and count all the rows that match PATTERN

-thing: turn off greed mode and show only what PATTERN can match.

-QQuiet.com: quiet mode, no matching results are output

-- color [= WHEN],-- colour [= WHEN]: highlight content that matches PATTERN in a special color

-Emam grep talk: extended regular expression, Emam-E is equivalent to egrep

-Freguipr fgrep-F is equivalent to Fleming.

Basic egrep regexp: basic regular expression, Gmam-G equals grep

The PCRE (Perl Regular Expression) engine is used.

-A NUM,--after-context=NUM: displays the following NUM lines while displaying the lines that match the PATTERN

-B NUM,-- before-context=NUM: displays the previous NUM line while displaying the line that matches the PATTERN

-C NUM,-NUM,-- context=NUM: display the NUM lines before and after the lines that match the PATTERN

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:] 、 [: alnum:] 、 [: punct:] 、 [: blank:]

[: xdigit:]: all hexadecimal numbers

Amurz: all lowercase letters

Amurz: all capital letters

0-9: identifies all decimal digits

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 or 1)

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

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

\ {mdirection n\}: the character preceding it appears at least m times and at most n times; (m