Cigarette smoker---------Text processing of Linux Egre and fgrep of Three Musketeers

Egrep is another mode of grep, with the-e option (enabling or shutting down one or more of the commands), enabling the extended Regular expression engine feature to use patterns that extend the regular expression character and the combination of plain text characters , A line-by-line check of text flow that displays the row of the matched string to the standard output

The FGREP,GREP-F option, which turns off the regular expression engine feature, combines plain text characters withpattern, based on a unique algorithm, checks the text for efficient matching , and matches the line where the string is located display to standard output

Egrep command

[[Email protected] ~]# type Egrepegrep is aliased to ' egrep--color=auto ' [[email protected] ~]# which--skip-alias egrep/u Sr/bin/egrep[[email protected] ~]# egrep--help #获取使用帮助Usage: grep [OPTION] ... PATTERN [File]...-e,--extended-regexp #ERE # Its helper content with the use of the grep command

-e option, grep-e equivalent to Egrep

# grep-e ' ^root\b '/etc/passwd# egrep ' ^root\b '/etc/passwd

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Extending Regular Expression characters

Character matching

Number of Matches

Position anchoring

Or

Character matching

1). Any single character

2) [] any single character within the specified range, [ABC] A or B or C

3) [^] any single character outside the specified range

Using the example

[[email protected] ~]# vim a.txt #vim是一个文本编辑命令, enter after pressing I key, before writing text, after writing finished. Press the ESC key, and then press SHIFT +: to enter the Wq plus enter key. How is you?hwo old is you? How is it? HWO old is You?root:x:0:0:root:/root:/bin/bash

. Match any single character

# egrep ' R.. T ' a.txt

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[] matches any single character within the specified range, [ABC] A or B or C

# egrep ' [EFH] ' a.txt

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[^] denotes any single character outside the specified range, [^ABC] not A and B and C

# egrep ' [^efh] ' a.txt

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Number of matches Number of occurrences of the preceding single character

1) * matches the preceding single character, appears 0, 1, or more

2)? Matches the preceding single character, 0 or 1 times

3) + matches the previous single character, appears at least 1 times, >=1 times

4) {m} exactly matches the preceding single character m times

5) {m,} matches the preceding single character, at least m times

6) {, n} up to n times

7) {M,n} at least m times, up to N times

Using the example

[Email protected] ~]# vim Output_delimiter.txtabcba12baababbabababababababab

* matches the preceding single character, appearing 0, 1, or more

# egrep ' a*b ' output_delimiter.txt

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. * match. Any single character any time, any character of any length , (* in Glob)

# egrep ' r.*t ' a.txt

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? matches the preceding single character, 0 or 1 times ( in the basic regular expression \? )

# egrep ' a?b ' output_delimiter.txt # grep ' a\?b ' output_delimiter.txt

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+ matches the preceding single character, appearing at least 1 times, >=1 times ( \+ in the basic regular expression )

# egrep ' a+b ' output_delimiter.txt# grep ' a\+b ' output_delimiter.txt

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{m} exactly matches the preceding single character m times ( \{m\} in the basic regular expression )

# egrep ' a{3}b ' output_delimiter.txt# grep ' a\{3\}b ' output_delimiter.txt

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{m,} matches the preceding single character, at least m times ( \{m,\} in the basic regular expression )

# egrep ' a{3,}b ' output_delimiter.txt# grep ' a\{3,\}b ' output_delimiter.txt

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{, n} matches the preceding single character up to n times ( \{m,\} in the basic regular expression )

# egrep ' a{,2}b ' output_delimiter.txt# grep ' a\{,2\}b ' output_delimiter.txt

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{m,n} matches the preceding single character at least m times, up to N times ( \{m,n\} in the base regular expression )

# egrep ' a{3,6}b ' output_delimiter.txt# grep ' a\{3,6\}b ' output_delimiter.txt

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Position Anchor ' expected matching character must appear in a certain location '

1) ^ The beginning of the line anchor, used for the leftmost mode. by The string character that the regular expression matches to must appear at the beginning of the line

2) $ line end anchor for the right side of the pattern. A string character that is matched by a regular expression must appear at the end of the line

3) ^pattern$: The entire line can only match this mode

4) Match blank line: ^[[:space:]]*$ blank can have any number of times

5) \< or \b The first anchor for the left side of the word pattern

6) \> or \b ending anchor for the right side of the word pattern

7) \<pattern\> or \bpattern\b matches the entire word for the left and right sides of the word

8) grouping, back reference ()

^ The beginning of the line is anchored to the left of the pattern. by The string character that the regular expression matches to must appear at the beginning of the line

# grep-e ' ^root '/etc/passwd

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$ line-tail anchor for the right-most mode. A string character that is matched by a regular expression must appear at the end of the line

# grep-e '/bin/bash$ '/etc/passwd

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^pattern$: The entire row can only match this pattern

# GREP-E-C ' ^$ '/etc/init.d/functions #匹配空行-C Displays the number of rows for all rows that match the string

Match blank line: ^[[:space:]]*$ blank can have any number of times

# GREP-E-C ' ^[[:space:]]*$ '/etc/init.d/functions #匹配可为空行或有空白字符的行

\< or \b The first anchor for the left side of the word pattern

# grep-e ' \broot '/etc/passwd

\> or \b Ending anchor for the right side of the word pattern

# grep-e ' root\b '/etc/passwd

\<pattern\> or \bpattern\b matches the entire word for the left and right sides of the word

# grep-e ' \broot\b '/etc/passwd

() grouping, ( the basic regular expression in \ (\) ) will be any character currently the same component

# Cat Grep.txt Abxyxxxxxxyxyxyxyxyabcxy

# grep-e ' (XY) + ' Grep.txt

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Attention:

When representing the string itself , if the command used by the regular expression character, there is \, then no \; If there is no \, then add \.

# Grep-o ' [[: alpha:]_]\+ () '/etc/rc.d/init.d/functions #正则表达式字符为 \ (\)

GREP-E-O ' [[: Alpha:]_]+\ (\) '/etc/rc.d/init.d/functions #扩展正则表达式字符为 ()

A back reference, the contents of the pattern in the grouping brackets are recorded in internal variables by the regular expression engine , and are named as: \1,\2,\3

# grep-e ' (^[[:alnum:]]+\>). *\1$ '/etc/passwd

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Or

[Ccat] C or C or a or T

c| Cat C or Cat

(c| C) at cat or cat

# Vim Dsdci.txtcatcatc12c123at

1, [Ccat] matches any single character within the specified range

# egrep ' [Ccat] ' dsdcI.txt

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2, c| Cat matches C or cat

# egrep ' c| Cat ' DsdcI.txt

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3, (c| C) at match cat or cat

# egrep ' (c| C) at ' DsdcI.txt

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Cigarette smoker---------Text processing of Linux Egre and fgrep of Three Musketeers