How to put command line parameter to shell script

Question

I have a executable shell script name project2. Following is one of the instruction my teacher gave me on the project.

This script must accept at least one command line parameter: the directory where its output is to be placed. If that directory is not given on the command line, the script should use a reasonable default directory.

Can you please tell me how can I make my script accept a command line. I haven't done anything like that before. Any help would be greatly appreciated. Thanks a lot.

Answer 1

For bash, command line parameters are stored in $1, $2, and so on, while $# will give you the count. In addition, shift can be used to shift them all "left" by one position and drop the count.

The following script is a good starting point for understanding how the parameters work:

echo $#
while [[ $# -gt 0 ]] ; do
    echo "$1"
    shift
done

When you run it with:

./myprog.sh hello there my name is "pax     diablo"

the output is:

6
hello
there
my
name
is
pax     diablo

The basic idea of your assignment is:

• check the parameter count to see if it's zero.
• if it is zero, set a variable to some useful default.
• if it isn't zero, set that variable based on the first parameter.
• do whatever you have to do with that variable.

Answer 2

Take a look at this section of Advanced Bash Scripting guide.

I recommend you to read whole guide.