Shell Judgment Statement--Example interpretation

1 if statement

The format of the IF statement:

If condition then command fi

If condition then command else command fi

If condition then command elif condition then command else command fi

Example:

Determines whether the current user is root, and if so, performs/home/test directory compression

#！ /bin/bash

If ["$ (id-u)"-eq "0"];then

Tar czf/home/test.tar.gz/home/test

Fi

Require the user to enter a password and determine if the password is correct

#！ /bin/bash

Read-p "Enter a passwd:" passwd

If ["$passwd" = = "123456"];then

echo "ok!"

Else

echo "error! Please input your passwd again "

Fi

Judging the score, less than 60 shows a failure, greater than 60 less than 70 display generally, greater than 70 less than 85 shows good, greater than 85 excellent

#！ /bin/bash

if [$1-ge];then

echo "Excellent"

elif [$1-ge];then

echo "Good"

elif [$1-ge];then

echo "General"

Else

echo "Failed"

Fi

Case statement

It is a replacement solution for multiple if statements and is easy to read and write

Format 1:

Case $ variable name in

Mode 1)

Command

;;

Mode 2)

Command

;;

Mode 3)

Command

;;

*)

Esac

Format 2:

Case $ variable name in

Mode 1| Mode 2)

Command

;;

Mode 3| Mode 4)

Command

;;

Mode 5| mode 6)

Command

;;

*)

Esac

Example:

Process/var/log log directory, backup only Wednesday Friday data, delete Tuesday Thursday data

#/bin/bash

date=$ (Date +%a)

time=$ (Date +%y+%m+%d)

Case DATE in

wed| Fri)

tar-czf/home/log/${time}_log_tar.gz/var/log/& >/dev/null

;;

tue| Thu)

Rm-rf/var/log/*.2016-*.log

;;

*)

Esac

Determine whether the input is a number or a letter

#/bin/bash

Case $ in

[A-z] | [A-z])

echo "You have type a character"

;;

[[:d Igit:]])

echo "This is a number"

;;

*)

Esac

This article is from the "Practical Linux knowledge and Skills sharing" blog, please be sure to keep this source http://superleedo.blog.51cto.com/12164670/1889263

Shell Judgment Statement--instance interpretation