Shell Passing Arguments
April 16, 2020
Arguments can be passed to the script when it is executed,we can get the arguments by the formats like $n.Inside the script, the $1 variable references the first argument in the command line, $2 the second argument and so forth.
For example
In the following example, the script name is followed by 3 arguments and will output these arguments separately and the variable $0 references to the current script file name.
#!/bin/bash
# author:ylspirit
# url:www.linuxcommands.site
echo "shell passing arguments example！";
echo "the current script file name：$0";
echo "the first argument：$1";
echo "the second argument：$2";
echo "the third argument：$3";Set executable permissions for the script, and execute the script, the output is as follows:
$ chmod +x test.sh
$ ./test.sh 1 2 3
shell passing arguments example！
the current script file name：./test.sh
the first argument：1
the second argument：2
the third argument：3The following table shows a number of special variables that you can use in your shell scripts
| Variable | Description |
|---|---|
| $# | The number of arguments supplied to a script. |
| $* | Represent all parameters passed to the script in a single string.All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2. |
| $$ | 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. |
| $@ | This is similar to the $*, but the difference is that $@ should add double quoted in which to get the arguments.All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to “$1” “$2”. |
| $- | Show the current opitions like shell command set |
| $? | The exit status of the last command executed. |
#!/bin/bash
# author:ylspirit
# url:www.linuxcommands.site
echo "shell passing arguments example！";
echo "the first argument：$1";
echo "the number of arguments：$#";
echo "show all parameters passed：$*";Execute the script, the output is as follows:
$ chmod +x test.sh
$ ./test.sh 1 2 3
shell passing arguments example！
the first argument：1
the number of arguments：3
show all parameters passed：1 2 3The differences between the $* and $@:
- similarities:represent all parameters
- differences:All the arguments are individually double quoted or not.If we pass three arguments like 1、2、3,” * ” is equal to “1 2 3″(pass one param),but “@” is equal to “1” “2” “3”(pass three params)
#!/bin/bash
# author:ylspirit
# url:www.linuxcommands.site
echo "-- \$* demo ---"
for i in "$*"; do
echo $i
done
echo "-- \$@ demo ---"
for i in "$@"; do
echo $i
doneExecute the script, the output is as follows:
$ chmod +x test.sh
$ ./test.sh 1 2 3
-- $* demo ---
1 2 3
-- $@ demo ---
1
2
3