Shell script basics ----- For Loop

Format

For name in list

Do

Loop body

Done

Example:

List the usernames, uid, and shell in the/etc/passwd file, Row 1, 3, 6, and 12

#!/bin/bashfor line in 1 3 6 12do        Username=$(head -$line /etc/passwd | tail -1 | awk -F: ‘{print $1}‘)        Userid=$(head -$line /etc/passwd | tail -1 | awk -F: ‘{print $3}‘)        Usershell=$(head -$line /etc/passwd | tail -1 | awk -F: ‘{print $7}‘)        echo -e "UserName:$Username\tUserID:$Userid\tUserShell:$Usershell"done

List generation

1. Give/etc/fstab/etc/inittab one by one

2. wildcard matching, for example,/var /*

3. Command production list

Example:

#!/bin/bashfor File in `ls /var`do    file /var/$Filedone

4. The number sequence {1 .. 100} is automatically expanded to 1 to 100.

{Start number... end number}

SEQ automatically generates a numerical sequence:

Sed 3: generated from 1 to 3

Sed 3 16 production from 3 to 16

Sed 3 2 16 generates 3 to 16, but the interval is 2

3 5 7 9 11 13 15

Exercise: display the usernames and shells of all/etc/passwd users.

#!/bin/bashLINES=$(wc -l /etc/passwd | awk -F" " ‘{print $1}‘)for I in $(seq 1 $LINES)do        head -$I /etc/passwd | tail -1 | awk -F: ‘{print $1,$7}‘done

Arithmetic Operations in shell scripts

Shell does not support floating point numbers: In the calculation result, the floating point will be an integer.

1.22 = 1; 1.99 = 1

Arithmetic Operation Implementation Method

$ [Expression]

For example

A = 1

B = 2

C = $ [$ A + $ B]

Echo $ C

3

Script contact

Calculate the sum of 0 to 100

#!/bin/bashsum=0for i in $(seq 0 100)do        sum=$[$sum+$i]doneecho $sum

Calculate the total uid of all users

#!/bin/bashidsum=0for i in $(awk -F: ‘{print $3}‘ /etc/passwd)do        idsum=$[$idsum+$i]doneecho $idsum

This article from the "hanging sword" blog, please be sure to keep this source http://sublime.blog.51cto.com/8856101/1440022

Shell script basics ----- For Loop