Shell Special Variable character interception

Shell Special variables

Variable meaning

$ $ Gets the script name of the currently executing shell script, including the path and script name if the script has a path

$n Gets the nth parameter in the currently executing shell script. But when n=1..9, but n is 0, indicates the file name of the script, and if n is greater than 9, it needs to be enclosed in curly braces, such as ${10}.

$# Get the total number of parameters in the current shell command line

All positional parameters of "$*" (as a single string) get all the parameters of the current shell script and treat all command-line arguments as a string.

"[Email protected]" all positional parameters (each as separate strings) get all the parameters of the current shell script, and each parameter of all command lines is treated as a separate string.

${#*} the number of command-line arguments passed to the script

${#@} the number of command-line arguments passed to the script

$? Gets the return value that executes the last instruction (0 is a success value, not 0 is a failure)

$$ Gets the process ID (PID) of the current execution script

$- The flags passed to the script (using set)

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

$! Process ID (PID) of the last job running in the background

* must be quoted, otherwise the default is "[email protected]".

DirName #获取当前脚本路径

BaseName #获取当前脚本名称

The difference between $* and [email protected]

$* and [email protected] All represent all parameters passed to a function or script, and are not enclosed by double quotation marks (""), with "$" and "$" ... All parameters are output in the form "$n".

But when they are enclosed in double quotation marks (""), "$*" takes all the parameters as a whole and outputs all parameters in the form of "$ $ ... $n"; "[email protected]" separates the various parameters to "$" "$" ... All parameters are output in the form "$n".

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Variable Quantum string

Meaning of an expression

${#string} length of $string

${string:position} $string, extract substrings starting from position $position

${string:position:length} $string, extract the substring of length $length starting from position $position

${string#substring} removes the substring of the shortest match $substring from the beginning of the variable $string

${string# #substring} Remove the substring of the longest matching $substring from the beginning of the variable $string

${string%substring} removes the substring of the shortest match $substring from the end of the variable $string

${string%%substring} Remove the substring of the longest matching $substring from the end of the variable $string

${string/substring/replacement} uses $replacement instead of the first matching $substring

${string//substring/replacement} uses $replacement instead of all matching $substring

${string/#substring/replacement}

If the $string prefix matches the $substring, then the $replacement is used instead of the matching $substring

${string/%substring/replacement}

If the $string suffix matches the $substring, then the $replacement is used instead of the matching $substring

This article is from the "Struggle Bar" blog, please be sure to keep this source http://lvnian.blog.51cto.com/7155281/1701156

Shell Special Variable character interception