How to Write a Shell Script to Display Command Line Argument Using $#, $@,$*,$$,$?$!

The following article demonstrates How to Write a Shell Script to Display Command Line Argument Using $#, $@,$*,$$,$?$!

Accordingly, a simple shell script that demonstrates the use of various special variables is given below.

#!/bin/bash

# Display the total number of command line arguments
echo "Total number of arguments: $#"

# Display all the command line arguments separated as individual strings using "$@"
echo "Using \"\$@\":"
for arg in "$@"; do
echo "$arg"
done

# Display all the command line arguments as a single string using "$*"
echo "Using \"\$*\":"
echo "$*"

# Display the process ID of the script using "$$"
echo "Process ID of the script: $$"

# Execute a non-existent command to set an exit status
non_existent_command
exit_status=$?

# Display the exit status of the last executed command using "$?"
echo "Exit status of last command: $exit_status"

# Display the process ID of the last background command using "$!"
sleep 5 &
background_pid=$!
echo "Process ID of last background command: $background_pid"

# Wait for background process to complete
wait $background_pid
echo "Background process has completed"

Make sure to save this script to a file, make it executable using chmod +x script_name.sh, and then run it with command line arguments.
For example, if you save the script as display_args.sh and run it like this.

./display_args.sh arg1 arg2 "arg 3" arg4

As a result, you will get the following output.

Total number of arguments: 4
Using "$@":
arg1
arg2
arg 3
arg4
Using "$*":
arg1 arg2 arg 3 arg4
Process ID of the script: <some_process_id>
./display_args.sh: line 16: non_existent_command: command not found
Exit status of last command: 127
Process ID of last background command: <background_process_id>
Background process has completed

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Further Reading

How to Write a Shell Script to Display Command Line Argument Using $#, $@,$*,$$,$?$!

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