Summary of several special shell variables in Linux

 

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Summary of several special shell variables:

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Special shell variables:

$0 get the name of the currently executed shell script

$ N obtain the nth parameter value of the currently executed shell script, n = 1 .. 9

$ * Get all parameters of the current shell "$1 $2 $3... Note the difference with $ #

$ # Obtain the total number of parameters in the Current Shell Command Line

$ Obtain the current shell process ID (PID)

$! PID used to execute the previous command

$? Obtain the returned value of the previous Command executed (0 indicates success, and non-zero indicates failure)

$ @ All parameters of this program "$1" "$2" "$3" "…"

Example ):

[Ryan @ etiantian test] # Cat etiantian. Sh

Echo '$0 get the name of the currently executed shell script:' $0

Echo '$ n get the nth parameter value of the currently executed shell script, n = 1 .. 9: ''$ 1' = $ 1' $ 2' = $2 '\ $3 = $3 ″

Echo '$ * Get all parameters of the Current Shell' $1 $2 $3... Note the difference with $ #: '$ *

Echo '$ # obtain the total number of parameters in the current shell command line:' $ #

Echo '$ obtain the current shell process ID (PID):' $

Sleep 2 &

Echo '$! PID for executing the previous command: '$!

Echo '$? Obtain the returned value of the previous command: '$?

Echo '$ @ all parameters of this program "$1" "$2" "$3" "…" : '$ @

Script Execution results (carefully read ):

[Ryan @ etiantian test] # sh etiantian. Sh parameter 1 parameter 2 parameter 3

$0 get the name of the currently executed shell script: etiantian. Sh

$ N get the nth parameter value of the currently executed shell script, n = 1 .. 9: $1 = parameter 1 $2 = parameter 2 $3 = parameter 3

$ * Get all parameters of the current shell "$1 $2 $3... Note the difference with $ #: parameter 1 parameter 2 parameter 3

$ # Obtain the total number of parameters in the current shell command line: 3

$ Obtain the current shell process ID (PID): 2062

$! PID for executing the previous command: 2063

$? Obtain the returned value of the Last Command executed: 0

$ @ All parameters of this program "$1" "$2" "$3" "…" : Parameter 1 parameter 2 parameter 3

[Ryan @ etiantian test] # sh etiantian. Sh Ryan jeacen David

$0 get the name of the currently executed shell script: etiantian. Sh

$ N get the nth parameter value of the currently executed shell script, n = 1 .. 9: $1 = Ryan $2 = jeacen $3 = David

$ * Get all parameters of the current shell "$1 $2 $3... Note the difference with $ #: Ryan jeacen David

$ # Obtain the total number of parameters in the current shell command line: 3

$ Obtain the current shell process ID (PID): 2160

$! PID for executing the previous command: 2161

$? Obtain the returned value of the Last Command executed: 0

$ @ All parameters of this program "$1" "$2" "$3" "…" : Ryan jeacen David