1.6 linux basis (f) grep Three Musketeers

1.6 linux basis (f) grep Three Musketeers

grep: Global search REgular expression and Print out the line

Line to match the print; text search tool, based on user-specified "model" for the target text line by line matching check: the role of

Mode: filtering criteria by the regular expression characters and text characters written

grep [OPTIONS] PATTERN [FILE...]

• grep root /etc/passwd

• grep "$USER" /etc/passwd

• grep '$USER' /etc/passwd

• grep `whoami` /etc/passwd

grep command options:

• --color = auto: matching the color display of the text

• -v: show no pattern is matched to the line

• -i: Ignore character case

• -n: display the line numbers match

• The number of rows that match Statistics: -c

• -o: Display only the matched character string

• -q: silent mode does not output any information

• -A #: after, after # line (look for signs)

• -B #: before, before the line #

  ~]# nmap -v -sP 192.168.32.0/24 |grep -B1 up|grep "Nmap scan" |cut -d" " -f5

• -C #: context, each longitudinal row #

• -e: to achieve a logical relationship between the number of options or

• grep –e 'cat ' -e 'dog' file

• -w: match whole words

• -E: Use ERE, extended regular expressions

• -F: the equivalent of fgrep, does not support regular expressions (look fast)

1.6.1 Regular Expressions

• REGEXP: a special kind of mode character and text written characters, some characters (metacharacters)

• Does not represent a character literal meaning, while a control function or wildcard

• Program support: grep, sed, awk, vim, less, nginx, varnish, etc.

• Divided into two categories:

  • The basic regular expressions: BRE

  • Extended regular expressions: ERE grep -E, egrep

The regular expression engine:

Using different algorithms, check processing software modules regular expression

PCRE（Perl Compatible Regular Expressions）

Metacharacters Category: character, the matching frequency and location of anchors, group

man 7 regex

== Basic == regular expression metacharacters

1.6.1.1 character matches:

• . Matches any single character

• [] Matches any single character within a specified range

• [^] Any single character match outside the specified range

• [: alnum:] letters and numbers

• [: alpha:] represents any case English characters, i.e. AZ, AZ

• [: Lower:] lowercase

• [: Upper:] uppercase letters

• [: digit:] decimal number

• [: punct:] Punctuation

• [: space:] the horizontal and vertical whitespace

• [: Blank:] white space (spaces and tabs)

• [: Space:] vertical and horizontal whitespace (ratio [: blank:] contains a wide range)

• [: Cntrl:] unprintable control character (backspace, delete, bell ...)

• [: Xdigit:] hexadecimal digits

• [: Graph:] non-blank printable characters

• [: Print:] printable characters

1.6.1.2 the number of matches

• After the character to be used in a specified number of times specified for the preceding character to appear

  • *: Any number of times in front of the match character, including zero

  • Greed mode: as long as possible match

  • * Any character of any length

  • ? Matches its preceding character 0 or 1 times

  • Match front + character at least once

  • {N} matches the preceding character n times

  • {M, n} m character match at least the front and at most n times

  • {, N} foregoing character match up to n times

  • {N,} matches at least n times the previous character

1.6.1.2 anchoring position: positioning to appear

• ^ Beginning of a line anchored mode for most of the left
  
• $ Anchored end of the line, for the rightmost pattern
  
• ^ PATTERN $ pattern matching for the whole line
  
• ^ $ Empty line
  
• ^ [[: Space:]] * $ Blank lines
  
• <Or \ b word-initial anchor for word patterns of the left
  
• > Or \ b suffix anchor; right mode for the word
• <PATTERN> matches the entire word

1.6.1.3 Grouping:

• () One or more characters tied together, as a whole for processing

• Such as: (root) + parentheses packet pattern matching content to be recorded in the regular expression engine of internal variables, these variables are named: \ 1, \ 2 \ 3, ...

• \ 1 showing from the left a first mode between the left bracket and a right bracket matching the matched character

Example: (string1 + (string2) *)

\1 ：string1+(string2)*

\2 ：string2

After the reference to 1.6.1.4

• Reference packet mode in parentheses preceding the matching characters, rather than the pattern itself

[root@centos7 ~]# cat 1.txt 
He love his lover.
She like her liker.
He like his lover.
[root@centos7 ~]# cat 1.txt |egrep "(love)+.*\1"
He love his lover.

1.6.1.5 Or: |

• Example: a | b: a or B
  C | cat: C or cat
  (C | C) AT: Cat or cat

Exercise:

1, the display / proc / meminfo file to the beginning of the line size s (requirement: two methods)

[root@CentOS7 scripts]# cat /proc/meminfo |grep -E "^(s|S)"
SwapCached:            0 kB
SwapTotal:       3145724 kB
SwapFree:        3145724 kB
Shmem:             10640 kB
Slab:             119216 kB
SReclaimable:      59848 kB
SUnreclaim:        59368 kB

[root@CentOS7 scripts]# cat /proc/meminfo |grep  "^[sS]"

SwapCached:            0 kB
SwapTotal:       3145724 kB
SwapFree:        3145724 kB
Shmem:             10640 kB
Slab:             119216 kB
SReclaimable:      59848 kB
SUnreclaim:        59368 kB
[root@CentOS7 scripts]# cat /proc/meminfo |grep -i "^s"
SwapCached:            0 kB
SwapTotal:       3145724 kB
SwapFree:        3145724 kB
Shmem:             10640 kB
Slab:             119232 kB
SReclaimable:      59848 kB
SUnreclaim:        59384 kB

2, the display / etc / passwd file not to / bin / bash line end

[root@CentOS7 scripts]# cat /etc/passwd |grep -v "/bin/bash$"

3, displays the user's default shell program rpc

[root@CentOS7 scripts]# cat /etc/passwd |grep "rpc\>"|cut -d : -f7
/sbin/nologin

4, to find the / etc / passwd in two or three digits

[root@CentOS7 scripts]#  cat /etc/passwd|grep "\<[1-9][0-9]\{1,2\}\>"

5, display /etc/grub2.cfg file CentOS7, at least to begin with a blank line of characters and there is a non-blank character behind

[root@CentOS7 scripts]# cat /etc/grub2.cfg |grep "^[[:space:]]\+[^[:space:]]\+"   
[root@CentOS7 scripts]#cat /etc/grub2.cfg |grep "^[[:space:]]\{1,\}[^[:space:]]\{1,\}"

6, to find the "netstat -tan" command followed by the results to the end of any number of white space characters LISTEN line

[root@CentOS7 scripts]# netstat -tan|grep "LISTEN[[:space:]]*$"

7, displays the user names of all system users on CentOS7 and UID

[root@CentOS7 scripts]# cat /etc/passwd |grep "/sbin/nologin"|cut -d":" -f1,3

8, adding users bash, testbash, line basher, sh, nologin (its shell to / sbin / nologin), find / etc / passwd username and shell of the same name

[root@CentOS7 scripts]# cat /etc/passwd |grep "^\([[:alnum:]]\+\>\).*\1$"

9, and the use of df grep, remove the disk usage of each partition, and descending order

[root@CentOS7 scripts]# df|grep "/dev/sd.*"|tr -s " "  |cut -d" " -f1,5 |sort  -n
    /dev/sda1 16%
    /dev/sda2 9%
    /dev/sda3 1%
[root@CentOS7 scripts]# df|grep "/dev/sd.*"|tr -s " "  |cut -d" " -f1,5|sort -t" " -k2 -nr
    /dev/sda1 16%
    /dev/sda2 9%
    /dev/sda3 1%

[root@CentOS7 ~]# df |grep "/dev/sd"|egrep -o "[0-9]{1,3}%"

1.6.1.6 egrep extended regular expressions

egrep = grep -E

egrep [OPTIONS] PATTERN [FILE...]

• Extended regular expression metacharacters:

• Character matches:

  • . Any single character

  • [] Specified range of characters

  • [^] Not in the specified range of characters

• The number of matches :

  • * : Matches the previous character any number of times

  • ?: 0 or 1

  • +: 1 or more times

  • {M}: m times Match

  • {M, n}: at least m, up to n times

• Anchor position:

  • ^: Beginning of the line

  • $: End of line

  • <, \ B: First word

  • >, \ B: suffix

• Packet: ()

• After the quote: \ 1, \ 2, ...

• Or: a | b: a or b

  • C | cat: C or cat

  • (C|c)at:Cat或cat

1.6.2 Exercise

1, shows three users root, mage, wang UID and default shell

[root@CentOS7 scripts]# cat /etc/passwd |egrep "^(root|mage|wang)\>"|cut -d: -f1,3,7
root:0:/bin/bash
mage:4035:/bin/bash
wang:4049:/bin/bash

2, first find out /etc/rc.d/init.d/functions lines in the file for a word (underscore) followed by a row of small parenthesis

[root@CentOS7 scripts]# cat /etc/rc.d/init.d/functions |egrep "^[[:alnum:]_]+\>\("

3, taken egrep using its group name /etc/rc.d/init.d/functions

[root@CentOS7 scripts]# echo  /etc/init.d/functions/ |egrep -o "[^/][[:alnum:]_]+/?$"
[root@CentOS7 scripts]# echo  /etc/init.d/functdfioj_123/ |egrep -o "[^/]+/?$"
functdfioj_123/

4, the top directory name removed using egrep path

[root@CentOS7 scripts]# echo  /etc/init.d/functdfioj_123/ |egrep -o "/.*/?$"

5, each host stats last command logged in as root IP address of logins

[root@CentOS7 scripts]# last |egrep -o "\<([1-9]|[1-9][0-9]|1[1-9][0-9]|2[0-4][0-9]|25[0-5])\>\.([1-9]|[1-9][0-9]|1[1-9][0-9]|2[0-4][0-9]|25[0-5])\>\.([1-9]|[1-9][0-9]|1[1-9][0-9]|2[0-4][0-9]|25[0-5])\>\.([1-9]|[1-9][0-9]|1[1-9][0-9]|2[0-4][0-9]|25[0-5])\>" |sort|uniq -c 
  1 172.16.253.196
103 192.168.110.1
  1 192.168.110.128

6, using the extended regular expressions represent 0-9,10-99,100-199,200-249,250-255

0-9:[0-9]
10-99:[1-9][0-9]
100-199:1[0-9][0-9]
200-249:2[0-4][0-9]
250-255:25[0-5]

7, shows all IPv4 addresses ifconfig command results

 ifconfig |egrep -o "([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-5]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-5]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-5]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-5]|25[0-5])" 

[root@centos6 ~]# hostname -I 
192.168.24.6 

8, this string: welcome to centos linux

Each character and to re-sort, many repetitions discharged to the front

[root@CentOS7 scripts]# echo "welcome to magedu linux "|egrep -o "[[:alpha:]]"|sort |uniq -c|sort -nr
3 e
2 u
2 o
2 m
2 l
1 x
1 w
1 t
1 n
1 i
1 g
1 d
1 c
1 a

echo "welcome to magedu linux"|sed 's/[[:space:]]/\n/g'|sed -r 's/([[:alpha:]])/\1\n/g'|sed '/^$/d'|sort |uniq -c |sort -nr