Shulou(Shulou.com)06/02 Report--

Four-condition test

Test test condition test content

[test condition test content] # is more widely used

1 Test file type

Test-e filename tests whether the file exists and is true

[- e file name] Note: spaces must be added on the left and right sides of []!

Attachment: test test results do not show, need to use echo$? To display the return value of test

The return 0 statement is correct, and a non-0 statement is incorrect.

Extension: test-e test.txt & & echo Yes | | echo No

Test-f file name determines whether it is a normal file # if it is a file, it returns 0, if the directory returns non-0

Test-d file name determines whether it is a directory or not

Test-b file name determines whether it is a block device file

Test-c filename character device file

2 Test file permissions

Test-r file name determines whether it has readable permissions

The test-w file name is writable

Test-x filename execution

Test-s file name determines whether it is non-blank and whether the content is true.

3 comparison of two documents

[file1-nt file2] whether file1 is newer than file2

[file1-ot file2] whether file1 is older than file2

[file1-ef file2] whether file1 and file2 are linked files, shortcuts, soft links

4. Judge between two values

[N1-eq N2] N1 and N2 are equal # it is recommended to use the following = = symbol to judge

Test: aa=123;bb=123

[$aa-eq $bb] & & echo Yes | | echo no

[N1-ne N2] N1 and N2 are not equal

[N1-gt N2] N1 is greater than N2

[N1-lt N2] N1 is less than N2

[N1-ge N2] N1 is greater than or equal to N2

[N1-le N2] N1 is less than or equal to N2

5 judgment string

[- z string] determines whether the string is empty, and the variable value is true if it has no content / is empty

[string 1 = = string 2] determines whether string 1 is equal to string 2 # determines whether string type is used

[$aa = = $bb] & & echo 1 | | echo 2

Attached: aa=abc

["$aa" = = "abc"] & & echo Yes | | echo No # Why is the test successful without two ""?

[string 1! = string 2] determine whether the string is unequal

6 multiple judgments

-a logic vs.

[- z $file-a-e $file]

-o logical or

! Logic is not

Example 7: determine the type of file entered and file permissions Note: be sure to practice

#! / bin/bash

Echo-e "nide wenjian shifou cunzai? wenjian quanxian shi shenme?\ n\ n"

Read-p "please input filename:"-t 30 filename

Test-z $filename & & echo "please input filename!" & & exit 1

# determine whether the string is empty, if so, print an error message, and exit the program!

Test!-e $filename & & echo "wenjian bucunzai!" & & exit 2

The #-e variable determines whether the file exists and whether it exists is true! Logic is not

Test-f $filename & & filetype=putong

Whether #-f is an ordinary file

Test-d $filename & & filetype=mulu

#-d whether it is a directory

Test-r $filename & & perm= "read"

#-r whether it has readable permission

Test-w $filename & & perm= "$perm write"

Whether #-w is writable

Test-x $filename & & perm= "$perm executable"

Whether #-x is executable

Echo-e "the filename is: $filename\ n"

# print file name

Echo-e "filetype is: $filetype\ n"

# print file type

Echo-e "permision is: $perm\ n"

# permission to print files

Five process control

1 if statement

1) if conditional statement-- single branch. Perform the appropriate action when the condition is established

Format:

If conditional test command

Then command sequence

Fi

Example 8:

If the space usage of the / boot partition exceeds 80%, output a warning

#! / bin/bash

RATE= `df-hT | grep "/ boot" | awk'{print $6}'| cut-d "%"-F1 `#: backquotes!

#: df command: displays partition usage

If [$RATE-gt 80]

Then

Echo "Warning,/boot DISK is full!"

Fi

2) if conditional statement-double branches. Perform different actions when "conditions are established" and "conditions are not valid"

Format:

If conditional test command

Then command sequence 1

Else Command sequence 2

Fi

Example 9:

Determine whether the httpd service is started, and start if it is not started

#! / bin/bash

Http= `netstat-tlun | awk'{print $4 "\ n"}'| grep ": 80 $" `

(or http=$ (ps aux | grep httpd | grep-v grep))

Attached: netstat-tlun is used to view all ports started by the system

Psaux is used to print all the processes of apache

Grep-v grep reverses lines that contain grep

If [- z "$http"]

Then

Echo "httpd meiyou qidong!"

/ etc/rc.d/init.d/httpdstart

Else

Echo "httpd runing"

Fi

Add: stop Apache:servicehttpd stop

3) if conditional statement-multi-branch

Format:

If conditional Test Command 1; then

Command sequence 1

Elif conditional Test Command 2; then

Command sequence 2

Elif...

Else

Command sequence n

Fi

Example 10:

# judge the character entered

#! / bin/bash

Echo "if you want to beijing, please input 1"

Echo "if you want to shanghai, please input 2"

Echo "if you want to chengdu, please input 3"

Read-p "please input a num:"-t 30 num

If ["$num" = = "1"]

Then

Echo "beijingling cake!"

Elif ["$num" = = "2"]

Then

Echo "shanghaixiajiao!"

Elif ["$num" = = "3"]

Then

Echo "Chengduqiqiao!"

Else

Echo "error,please input 1 or 2 or 3."

Fi

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