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UNIX TUTORIALS - Unix - Special Variables

Unix - Special Variables

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VariableDescription
$0The filename of the current script.
$nThese variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on).
$#The number of arguments supplied to a script.
$*All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2.
$@All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2.
$?The exit status of the last command executed.
$$The process number of the current shell. For shell scripts, this is the process ID under which they are executing.
$!The process number of the last background command.

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$echo $$



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29949


						
Command-Line Arguments:


#!/bin/sh

echo "File Name: $0"
echo "First Parameter : $1"
echo "First Parameter : $2"
echo "Quoted Values: $@"
echo "Quoted Values: $*"
echo "Total Number of Parameters : $#"


						


$./test.sh Zara Ali
File Name : ./test.sh
First Parameter : Zara
Second Parameter : Ali
Quoted Values: Zara Ali
Quoted Values: Zara Ali
Total Number of Parameters : 2


						
Special Parameters $* and $@:


#!/bin/sh

for TOKEN in $*
do
   echo $TOKEN
done


						


$./test.sh Zara Ali 10 Years Old
Zara
Ali
10
Years
Old


						
Exit Status:


$./test.sh Zara Ali
File Name : ./test.sh
First Parameter : Zara
Second Parameter : Ali
Quoted Values: Zara Ali
Quoted Values: Zara Ali
Total Number of Parameters : 2
$echo $?
0
$