Getting Started with Shell Programming (second Edition) (middle)

variable test Statement-test

Function: Used to test whether the variable is equal, is empty, file type, and so on.

Format:

Test tested Condition or []#范围: Integer, String. File

1) integer test :

Test int1-eq int2 test integers are equal

Test int1-ge int2 Test int1 whether >=int2

Test int1-gt int2 Test int1 whether >int2

Test int1-le int2 test int1 whether <=int2

Test int1-lt int2 Test int1 whether <int2

Test int1-ne int2 test integers are not equal

2) string test :

Test STR1=STR2 test strings are equal

Test STR1!=STR2 test string is not equal

Test str1 test string is not empty

Test-n str1 test string is not empty

Test-z str1 test string is empty

3) file Test :

test-d file Specifies whether files are folders

Test- F file Specifies whether files are regular files

Test-x file Specifies whether files can be run

Test-r file Specifies whether the files are readable

Test-w file Specifies whether files are writable

test-a file Specifies whether the file exists

test-s file the size of the file is not 0

Note: Test test statements are generally not used alone , generally as a test condition of the IF statement , such as ;

If test-d filethen....fi

The abbreviated form of the variable for test "[]"

Demo Sample -apachtest.sh

#!/bin/bash# A Test shell script for test Apache was running or notweb=$ (/usr/bin/pgrep httpd) echo "Now let's test the APAC He ... "echo#if [" $web "! =" "]if [-N" $web "]then    echo" Apache is running ... "Else    echo" Apache is not running ... "    /etc/rc.d/init.d/httpd Startfi

Process Control Statements

Flow control Statement : The process used to control the Shell program

Exit statement : exit the program to run , and return a return code , return code 0 indicates normal exit , non- 0 indicates an abnormal exit.

For example : Exit 0

First, if

if/ Then format

Demo Sample -if_then.sh

#!/bin/bash# A Test shell script for if/thenif [-x/etc/rc.d/init.d/httpd]then    echo "script:/ETC/RC.D/INIT.D/HTTDP Have x power! "    /ETC/RC.D/INIT.D/HTTPD Restartfi

If/else Format

Union of multiple conditions :

-A: Logical and , the result is true only if two conditions are set .

-O: Logical OR , Two conditions only need to have a set up , The result is true.

Demo Sample-if_else.sh

#!/bin/bash# a test shell script for if/elif/elseecho-n "please input A filename:" Read Filenameif [-D $filename]then
   echo "$filename is a directory" elif [-F $filename]then    echo "$filename is a commen file" elif [-C $filename-O-B $filename]then    echo "$filename is a device file" Else    echo "$filename is a unkown file" fi

Demo sample -if_elif_exit.sh

#!/bin/bash# A Test shell script for If/elifif [$#-ne 2] thenecho ' Not enough parameters ' exit 1fiif [$1-gt $]then
   echo "is great then $" elif [$1-lt $]then    echo "is little then $" Else    echo "is equal as $" fi

Second,for/in

Demo Sample-for.sh

#!/bin/bash# A Test shell script for ' for ' for day in Sunday Monday Tuesday Wednesday Thursday Friday Saturdaydo    echo " The day was $DAY "done

awk Command [Segment Extraction]

Awk-f field delimiter ' command '[single citation] #假设不用- f to specify the cut character, the default space

1 . The user with UID 0 in thedetection system

Awk-f: ' $3==0 {print '} '/etc/passwd

#awk-F: ' {print $} '/etc/passwd

-F: Specifies that the cut is attached as:

$ A: third place for cutting

2, the detection system in the password is empty users

Awk-f: ' Length ($) ==0 {print $} '/etc/shadow

#ps aux | Grep-v Root | awk ' {print $} '

Demo Sample -awk.sh

#!/bin/bash# a test script for desplay users infomation/bin/echo-n "Please input A username:" Read Username/bin/grep $use  rname/etc/passwd >/dev/null 2>/dev/nullif [$?-eq 0]then/bin/echo "username is: $username" Else/bin/echo    "User: $username is not exits." Exit 1fi/bin/echo# list/etc/passwd infouserinfo= '/bin/grep ^ $username: x/etc/passwd ' uid= ' echo $userinfo | Awk-f: ' {print $} ' gid= ' echo $userinfo | Awk-f: ' {print $4 '} ' dir= ' echo $userinfo | Awk-f: ' {print $6} ' shell= ' echo $userinfo | Awk-f: ' {print $7} ' # Get/etc/group infogroupinfo= '/bin/grep x: $gid/etc/group ' gname= '/bin/echo $groupinfo | Awk-f: ' {print $} '/bin/echo ' User ID is: $uid "/bin/echo" default group is: $gname "/bin/echo" Home directory is: $dir "/b In/echo "Shell is: $shell"/bin/echo "group member Info:" # Get Group membersgroups= '/usr/bin/groups $username '/bin/echo $g roups/bin/echo# get online infoonline= '/usr/bin/who | grep $username ' If [-Z ' $online "]then echo" $username is not online "ElSe echo "$username is online ..." fi 

Example -killuser.sh

#思路: Shutting down a user's entire process containment shell is equivalent to kicking the user out of the system #!/bin/bash# a shell sript to kill a user in linuxusername=$1killpid= '/bin/ps aux | grep $username | awk ' {print $} ' for PID in $killpiddo    /bin/kill-9 $PID 2>/dev/nulldone

Getting Started with Shell Programming (second Edition) (middle)