Linux OPS Practice-August 27, 2015 Course assignments

Basic Regular Expression grep command

First, Summary:

grep, Egrep, Fgrep

Divided into two categories:

Basic Regular Expressions: BRE

Extended Regular expression: ERE

1. Grep:global Search REgular expression and Print out of the line.

Function: The text Search tool, according to the user-specified "pattern" line to search for the target text, print the matching line; pattern: a matching condition that is a combination of metacharacters of the text wildcards regular the expression, which can be enclosed in single quotation marks To avoid the effects of shell wildcard, strong references do not replace and display the characters themselves. "" Double quotes, "in the string,", $, \ And so on, are replaced by the shell interpretation and then passed to grep. The normal string (a string without special characters and spaces) can also be searched without quotation marks.

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

Syntax: grep [Options]pattern [FILE ...]

Common parameters:--color=auto: The matching to the string to do highlighting;

-V: The display mode does not match the row;

-I: ignore character case;

-O: Displays only strings that can be matched to the pattern;

-Q: Silent mode;

-C Displays the number of rows that are matched to

-N Output line number

-V reverse selection, which is to find rows without a search string

-W Match Word

-A # is displayed along with the next # line of the matching line, #代表任意数字

-B # is displayed along with the # line of the matching line, #代表任意数字

The-C # is displayed along with the top and bottom # lines of the matching row, #代表任意数字

-R or-R recursively searches for a matching word in the directory or subdirectory (can be combined with the Find command

-e equivalent to Egrep support for extended regular expressions

-F equivalent to Fgrep does not support regular expressions

Basic regular Expression meta-characters:

Character matching:.: matches any single character;

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

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

POSIX special character class: Can be viewed through Man 7 glob

[: Alpha:] literal character [a-za-z]

[:d Igit:] numeric characters [0-9]

[: Graph:] non-null characters (not spaces, control characters)

[: Lower:] lowercase characters [A-z]

[: Upper:] Uppercase characters [A-z]

[: Alnum:] [0-9a-za-z]

[: Cntrl:] control character

[:p rint:] non-null characters (including spaces)

[:p UNCT:] Punctuation

[: space:] All whitespace characters (new line, Space, tab), tab can also be represented by \ t

[: xdigit:] hexadecimal digits and letters (0-9,A-F,A-F)

We use this when we are using: [[: Alpha:]], if the inverse is [^[:d igit:]]

Number of occurrences: used to specify the number of times after the character;

*: any time;

\?:0 or 1 times;

\+:1 or multiple times;

\{m\}: Precisely limited to M times;

\{m,n\}: At least m times, up to n times, [M,n]

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

\{m,\}: at least m times;

. *: Matches any character of any length;

Location anchoring:

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

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

\< \b: The first anchor of the word; the left side of the pattern used to denote the word;

\> \b: the ending anchor; the right side of the pattern used to represent the word;

^$: blank line;

Group: \ (\)

The contents of the pattern in the grouped parentheses are recorded by the regular expression engine during execution, and the built-in variables are saved: The variables are \1, \2, ...

\1: From the left, the first opening parenthesis, and the matching right parenthesis in the middle of the pattern match to the content;

\2:

...

Back reference: Use a variable to refer to the character that matches the pattern in the preceding grouping brackets;

An extended regular expression:

The grep family has three commands:

grep: basic Regular expression

-e: extending regular expressions

-F: Regular expressions are not supported

Egrep: Extending Regular expressions

Fgrep: Regular expressions are not supported

Extend the metacharacters of regular expressions:

Character Matching:

.: Any single character

[]:

[^]:

Number of matches:

*

?: 0 or 1 times;

+: more than 1 times;

{m}: exact match m times;

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

Anchoring:

^: Anchoring the beginning of the line

$: Anchor Line End

\<, \b

\>, \b

Group: ()

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

Or:

A|b

C|cat: does not represent cat or cat, but is C or cat;

To be written (C|c) at

Second, practice

1. Display the lines in the/etc/passwd file that end with bash

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2. Display the two-digit or three-digit number in the/etc/passwd file

[[email protected] ~]$ grep-o ' [[:d igit:]]\{2,3\} '/etc/passwd 12 10 14 11 12 100 13 30 14 50 99 99 81 81 69 69 499 76 89 89 74 74 500 500 501 27 51 502 502 51 503 503 504 504

3. Display lines with ' LISTEN ' followed by 0, one or more whitespace characters in the ' Netstat-tan ' command result

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4. Add user bash, Testbash, basher, and Nologin user (Nologin user's shell

/sbin/nologin), and then find the line in the/etc/passwd file that has the same user name as its shell name

[[email protected] ~]$ grep ' ^\ (. *\):. *\1$ '/etc/passwd Sync:x:5:0:sync:/sbin:/bin/sync Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown Halt:x:7:0:halt:/sbin:/sbin/halt Bash:x:505:505::/home/bash:/bin/bash Nologin:x:508:508::/home/nologin:/sbin/nologin

5. Display the default shell and UID of root, CentOS, or User1 user on the current system (please create these users beforehand, if not present)

[[email protected] ~]$ grep-e ' ^ (root|centos|user1) '/etc/passwd | Cut-d:-f1,3,7 Root:0:/bin/bash Centos:509:/bin/bash User1:510:/bin/bash

6, find a word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses line

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7, use echo to output a path, and then egrep find its path base name; Further use Egrep to remove its directory name

[Email protected] ~]$ echo/usr/share/man/man8/iptables-1.4.7.8.gz | Egrep-o ' [^/]+/?$ ' Iptables-1.4.7.8.gz [Email protected] ~]$ echo/usr/share/man/man8/iptables-1.4.7.8.gz | Egrep-o ' ^/.*/' /usr/share/man/man8/

8. Find the number between 1-255 in the result of ifconfig command execution

Ifconfig | grep--color=auto ' [^[:alpha:]|0|[:p unct:]|[:space:]] '

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Linux OPS Practice-August 27, 2015 Course assignments