Lao Li share: "Linux shell Script Raiders" Essentials (iv)

1, the IP address of the regular expression: [0-9]{1,3}\. [0-9] {1,3}\. [0-9] {1,3}\. [0-9] {1,3}

2. grep usage

Recursive retrieval of text in a multilevel directory

[Email protected] program_test]# grep "yang"./-rn

./test.txt:6:laoyang
./right.txt:1:1 Yang Man

Ignore case matching

[Email protected] program_test]# echo Hello World | Grep-i "HELLO"
Hello World

recursively searches all. C and. cpp files

[[email protected] program_test]# grep "main ()". -R--include *. {C,cpp}
./hello.c:int Main ()
Sin.c:int Main ()
Hello.cpp:int Main ()

Match a few lines after a result

[Email protected] program_test]# echo-e "A\NB\NC\NA\NB\NC" | grep a-a 1
A
B
--
A
B

3. Cut command

Cut, a gadget that cuts text by column.

-D delimiter; -F Columns to extract

[Email protected] program_test]# cut-d ":"-f5--complement Passwd_yang
Root:x:0:0:/root:/bin/bash
Bin:x:1:1:/bin:/sbin/nologin

[Email protected] program_test]# cut-c1-5 Passwd_yang
Root
Bin:x
Daemo
Adm:x

Count the word frequency in a specific file

[email protected] program_test]# cat word_freq.sh

#!/bin/bash

If [$#-ne 1];

Then

echo "Usage: $ filename"

Exit-1

Fi

Filename=$1

Egrep-o "\b[[:alpha:]]+\b" $filename | \

awk ' {count[$0]++} \

END {printf ("%-14s%s\n", "word", "Count"); \

for (Ind in count) \

{printf ("%-14s%d\n", Ind,count[ind]);} }‘

4. Sed command (stream editor)

Apply text processing.

1. Replace, start with the 3rd one

[Email protected] program_test]# echo this thisthisthis | Sed ' s/this/this/3g '
This thisthisthis

2. Remove the blank line

[[Email protected] program_test]# sed '/^$/d ' choice.sh

3. Matched string Markers &

[Email protected] program_test]# echo This was an example | Sed ' s/\w\+/[&]/g '
[This] [IS] [An] [Example]

4. Replacement example.

[email protected] program_test]# cat Sed_data.txt
ABC 111 this 9 file contains 111 numbers 0000
[email protected] program_test]# Cat Sed_data.txt | sed ' s/\b[0-9]\{3\}\b/number3/g '
ABC NUMBER3 This 9 file contains NUMBER3 numbers 0000

5. Practical examples

Get an error message for NTP synchronization (assuming the current device is not networked)

Example one: Ntpdate 8.8.8.8

Jan 07:28:26 ntpdate[7137]: Bind () Fails:permission denied

Example two: Ntpdate google.com

[Email protected] cutdemo]# ntpdate msf22.com
Error resolving msf22.com:Name or service not known (-2)
Jan 07:30:54 ntpdate[7169]: Can ' t find host msf22.com:Name or service not known (-2)
Jan 07:30:54 ntpdate[7169]: No servers can be used, exiting

Want to get [71**]: After the error message, before the deletion. The script is as follows:

[Email protected] cutdemo]# ntpdate msft22.com 2>&1 | Sed ' s/.*\]\://g '
Error resolving msft22.com:Name or service not known (-2)
Can ' t find host msft22.com:Name or service not known (-2)
No servers can be used, exiting

Explanation: Ntpdate msft22.com 2>&1//2>&1 standard error redirect to standard output.

Sed ' s/.*\]\://g '//delete file "]:" in front of the string.

5. awk tool for data flow, operation on columns and rows.

1), how awk is implemented

[Email protected] program_test]# echo-e "Line1\nline2" | awk ' BEGIN {print ' begin...\n '} {print} END {print ' end...\n '} '
Begin ...

Line1
Line2
End ...

2), awk to achieve cumulative sum

[[email protected] program_test]# SEQ 5 | awk ' BEGIN {sum=0; print ' summary: '} {print ' + '; sum+=$1;} END {print "= =" Sum} '

Summary
1 +
2 +
3 +
4 +
5+
==15

3), awk sets the delimiter.

-F delimiter $NF the last field in a row

[Email protected] program_test]# awk-f: ' {print $ \ t ' $NF} '/etc/passwd
Root/bin/bash
Bin/sbin/nologin
Daemon/sbin/nologin

4), print each letter in the file

[email protected] program_test]# cat read_each_word.sh

Cat hello.c | \

(While read line;

Do

#echo $line;

for word in $line;

Do

#echo $word;

For ((i=0;i<${#word};i++))

Do

Echo ${word:i:1};

Done

Done

Done)

5), Print 4–6 line content

[[email protected] program_test]# SEQ 100 | awk ' nr==4, nr==6 '
4
5
6

6), awk to implement the function similar to TAC reverse order.

[[email protected] program_test]# SEQ 9 | awk ' {lifo[nr]=$0; Lno=nr} END {print "nr =" NR; for (; lno>-1;lno--) {print Lifo[lno];}} '

NR = 9

9

8

7

6

5

4

3

2

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Lao Li share: "Linux shell Script Raiders" Essentials (iv)