0 bash variable type:
environment variable
local variable (local variable)
location variable: $1, $2, ... respectively represent the first parameter, the second parameter ....
special variable
$?: Status code of last command execution result
$#: Number of parameters
$*: Parameter list
$@: Parameter list
1 Reference after variable assignment:
${varname} where {} can be omitted, as long as it will not cause confusion when used, then {} can be omitted
eg:
[root@h2sliver114 local]# name=zm
[root@h2sliver114 local]# echo "hello ${name}s." At this time, it is recommended to add {}
2 Introduction to specific variable types:
local variable: set VARNAME=VALUE: The scope is the entire bash process; local variable: local VARNAME=VALUE: the scope is the current code segment; Environment variables: The scope is the current shell process and its subprocesses; export VARNAME "export" position variable: $1, $2, ... Special variables: $?: The return value of the execution status of the previous command; Program execution, there may be two types of return values: program execution result Program status return code (0-255) 0: correct execution 1-255: Error execution, 1, 2, 127 system reservation;
3 View the environment variables in the current shell:
printenv This is the customary
env
export
4 Position variables:
eg:
sh filetest.sh /etc/fstab /etc/inittab $1: /etc/fstab $2: /etc/inittab
5 shift use:
shift 2 means to kick out 2 at a time to get the last of the two kicked out by default is to move 1
Use Cases:
#!/bin/sh # echo "the first param is: $1" shift echo "the second param is: $1" shift echo "the third param is: $1" result: [root@chinadaas109 zhoumingtest]# sh fortest.sh 1 2 3 the first param is: 1 the second param is: 2 the third param is: 3
6 Variables are assigned initial values:
${parameter:-word}: If parameter is empty or undefined, the variable is expanded to "word"; otherwise, it is expanded to the value of parameter; the so-called expansion is to print the result directly
${parameter:+word}: If parameter is empty or undefined, do nothing; otherwise, expand to "word" value;
${parameter:=word}: If parameter is empty or undefined, the variable is expanded to "word", and the expanded value is assigned to parameter;
${parameter:offset} Get the data from the beginning of the array script offset to the last character
${parameter:offset:length}: Take the substring, starting from the next character at offset (the index starts from 0), and take the substring with length;
Use Cases:
[root@chinadaas11 ~]# a=${a:-2}
[root@chinadaas11 ~]# echo $a
2
[root@chinadaas11 ~]# echo ${a:=30}
30
[root@chinadaas11 ~]# echo $a
30
[root@chinadaas11 ~]# a='hello world'
[root@chinadaas11 ~]# echo ${a:1:4}
it
[root@chinadaas11 ~]# echo ${a:1}
it world
7 Script to read configuration file
Usually in the following directory: /etc/rc.d/init.d/service script Service script support configuration file: /etc/sysconfig/configuration file with the same name as service script How to make the script use the configuration file: [root@chinadaas11 zm]# ll total 8 -rw-r--r-- 1 root root 10 Nov 2 14:48 a.conf -rw-r--r-- 1 root root 60 Nov 2 14:54 test.sh [root@chinadaas11 zm]# cat a.conf name='zm' [root@chinadaas11 zm]# cat test.sh #!/bin/bash # ./root/zm/a.conf ---> Equivalent to source /root/zm/a.conf Read and execute the commands in the file in the current bash environment [ -n $name ] && echo $name [root@chinadaas11 zm]# sh test.sh d