Shell Script Programming Learning notes-for loops

1.FOR Loop structure 1.1 for loop structure syntax

Grammar:

For variable name in variable Value list

Do

Instructions...

Done

Tip: In this structure, "in variable Value list" can be omitted, when omitted is equivalent to in "[email protected]", using for I is equivalent to I in "[email protected]".

1.2 C-language for loop structure

Grammar:

For ((EXP1;EXP2;EXP3))

Do

Instructions...

Done

Example: Comparison of While loops and for loops

[[email protected] jiaobenlianxi]# cat while4.sh #!/bin/bashi=1while((i<=10))do    echo $i    ((i++))done[[email protected] jiaobenlianxi]# cat for1.sh #!/bin/bashfor((i=1;i<=10;i++))do    echo $idone

Description

(1) The program continues to run multi-use while, including daemons and with read read into the loop processing.

(2) The finite-cycle multi-use for, the work for use more.

How to learn Memory:

For men in the world

Do

If [with room] && [car] && [deposit] && [will do housework] && [handsome] && [considerate] && [shopping] ; then

echo "I Like You"

Else

Rm–f Man

Fi

Done

1.3 For Loop Basic Example 1.3.1 Example 1: List all elements of a variable directly, print 1,2,3,4,5

Method 1:

[[email protected] jiaobenlianxi]#  cat for3.sh for n in 1 2 3 4 5 doecho $ndone

Method 2: Use the curly braces method

[[email protected] jiaobenlianxi]# cat for4.sh for n in {1..10}doecho 192.168.1.$ndone

Method 3: Use SEQ

[[email protected] jiaobenlianxi]# cat for5.sh for n in  `seq 5`doecho 192.168.1.$ndone

Prints the file name of the current directory with A For loop, implemented with SEQ

Tip: A variable Value list can also be used with command output

[[email protected] jiaobenlianxi]# cat for5.sh for n in  `ls`doecho $ndone

1.3.2 Example 2: Random number Generation file

Batch generated file, file name random MD5 processing, select eight bits.

[[email protected] jiaobenlianxi]# cat suijiwnjian.sh for((i=1;i<=10;i++))do    mkdir -p ./test    touch ./test/` echo $RANDOM|md5sum|cut -c 1-8`_finished.htmldone[[email protected] jiaobenlianxi]# ls test/0ac2453a_finished.html  8b90c52b_finished.html  c4eb22c9_finished.html2c1f5e87_finished.html  a22717d3_finished.html  db258218_finished.html6d6bc69f_finished.html  a4aca3b0_finished.html6d7c516a_finished.html  c21f3d55_finished.html

1.3.3 Example 3: Batch modification of file names

Modify the resulting 10 file ending in. html to end with. jpg. And remove the finished and use the For loop only.

Method One:

[r[email protected] jiaobenlianxi]# cat piliangxiugai1.sh for f in `ls test/*.html`do    mv $f `echo $f|sed ‘s#_finished.html#.jpg#g‘`done[[email protected] jiaobenlianxi]# ls test/0ac2453a.jpg  6d6bc69f.jpg  8b90c52b.jpg  a4aca3b0.jpg  c4eb22c9.jpg2c1f5e87.jpg  6d7c516a.jpg  a22717d3.jpg  c21f3d55.jpg  db258218.jpg

Method two: For loop plus variable partial intercept method

[[email protected] jiaobenlianxi]# cat piliangxiugai3.sh for file in `ls test/*.html`do    /bin/mv $file "${file%_finished*}.jpg"done

Method Three: LS combined with awk implementation

[[email protected] test]# ls0513d6f0_finished.html  6ab3573c_finished.html  8abfa660_finished.html1a9335f3_finished.html  70018e1c_finished.html  bb6763ab_finished.html559d16bc_finished.html  74e206b5_finished.html58fc15d7_finished.html  7878f84a_finished.html[[email protected] test]# ls |awk -F ‘[_]‘ ‘{print "mv " $0,$1".jpg"}‘|bash[[email protected] test]# ls0513d6f0.jpg  559d16bc.jpg  6ab3573c.jpg  74e206b5.jpg  8abfa660.jpg1a9335f3.jpg  58fc15d7.jpg  70018e1c.jpg  7878f84a.jpg  bb6763ab.jpg

Method Four: Realize by rename

[[email protected] test]# ls16d72ca3_finished.html  673c62da_finished.html  b9328787_finished.html37690b31_finished.html  72ebc17d_finished.html  e37aeed5_finished.html37e66161_finished.html  a5050e54_finished.html4efe1f4c_finished.html  b2553039_finished.html[[email protected] test]# rename "_finished.html" ".jpg" *[[email protected] test]# ls16d72ca3.jpg  37e66161.jpg  673c62da.jpg  a5050e54.jpg  b9328787.jpg37690b31.jpg  4efe1f4c.jpg  72ebc17d.jpg  b2553039.jpg  e37aeed5.jpg

1.3.4 Example 4:

Actual Case: Development script implementation only set SSHD Crond rsyslog network boot from

[[email protected] jiaobenlianxi]# cat chkconfigoff.sh LANG=enchkconfig --list|grep 3:on|awk ‘{print $1}‘ >b.logfor name in `chkconfig --list|grep 3:on|awk ‘{print $1}‘|egrep -v "sshd|crond|rsyslog|network"`do  chkconfig $name offdone[[email protected] jiaobenlianxi]# cat chkconfigon.sh LANG=enfor name in `cat b.log`do    chkconfig $name ondone

1.3.5 Example 5: Implementing the sum of 1-100 with a for loop

Method One:

[[email protected] jiaobenlianxi]# cat for1-100.sh for((i=1;i<=100;i++))do    let sum+=idoneecho $sum[[email protected] jiaobenlianxi]# sh for1-100.sh 5050

Method Two:

[[email protected] jiaobenlianxi]# cat for1-1000.sh for n in `seq 100`do    ((sum+=n))doneecho $sum

Method Three:

[[email protected] jiaobenlianxi]# cat for1-100_3.sh for n in `seq 100`do   a="$(($n*($n+1)/2))"doneecho $a

Shell Script Programming Learning notes-for loops