Shell Special variables

1. Positional variables

$ $ Gets the file name of the currently executing shell script, including the script path if the script is executed with a path

[[Email protected] shell]# sh n.sh n.sh[[email protected] ~]# sh/shell/n.sh/shell/n.sh[[email protected] shell]# sh ' pwd '/n.sh/shell/n.sh

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$n   Gets the nth parameter value of the currently executing shell script, n=1..9, when n is 0 indicates the file name of the script, if n is greater than 0, Braces enclosed ${10}

 script content: #!/bin/bashecho $1[[email protected] shell]# sh  p.sh xcn      #1个参数xcn                                                                                                                          [[email  protected] shell]# sh p.sh xcn cainiao     #2个参数输出的是第一个参数xcn 

$* gets all parameters of the current shell, treats all command-line arguments as a single string, equivalent to "$1$2$3" ... Note with the $ #的区域

$# gets the total number of parameters that are followed by the currently executing shell script

[email protected] shell]# cat p.sh echo $1echo $#[[email protected] shell]# sh p.sh {a.. Z}A26 Enterprise Application: (Control the number of user parameter input) when the input parameter is not equal to 2 set up the output "muse", the side will not output "Buchengli" [[email protected] shell]# cat 1p.sh #!/bin/bash[$# -ne 2] && {echo "Muse" Exit 1 #值1是退出后 $? value}echo "Buchengli" [[email protected] shell]# sh 1p.sh baimu Se two[[email protected] shell]# sh 1p.sh bai shubuchengli[[email protected] shell]#

[email protected] All parameters of this program "$" "$" "$" "...", this is the best way to pass parameters to other programs because he retains any whitespace embedded in each parameter.

Examples of differences between $* and [email protected]

• $* treats all command-line arguments as a single string, equivalent to "$1$2$3", "$*"

• [email protected] treats each parameter of the command line as a separate string, equivalent to "$" "$" "$ $". This is the closest way to pass parameters to other programs because he retains any whitespace embedded in each parameter.

Note: The above differences are only when double quotes are added, i.e. "$*" and "[email protected]"

Shift Move Position variable

2. Process state variables

$$ Gets the process number of the current shell

$! PID that executes the previous instruction

$? Gets the return value that executes the last instruction (0 is successful, nonzero is failed) #这个变量很常用

$_ the last parameter of a command or script executed before this

This article is from the "Little Rookie" blog, please be sure to keep this source http://baishuchao.blog.51cto.com/12918589/1939495

Shell Special variables