How to change the value of a function's parameter in linux script?

Question

I have a script which I call with different parameters. Depending on the value of those parameters I check out and build the 'parameter' SVN version of the project.

./deploy 3281 

This command will create a 3281 directory and check out the 3281 SVN version of the project and will build it in the 3281 directory.

I need to create a key word 'HEAD' so the script will check to see the latest SVN revision number and create a folder for it (ex: 3282 ) and then checkout the head version of the project and build it there.

I find out how to get the latest revision number with svn ( svn info -r 'HEAD' --username jse http://jse@svn.ctsvpn.com/repos/Teleena/ | grep Revision | egrep -o "[0-9]+" ) and I am trying to simply implement an if like this:

 #check to see if latest/head revision is called
        if [ "$1" == "head" ]; then
                #get latest revision number
                HEADREV=$(svn info -r 'HEAD' --username jse http://jse@svn.ctsvpn.com/repos/Teleena/ | grep Revision | egrep -o "[0-9]+")
                echo "=========================================="
                echo "= Revision number: $HEADREV will be used ="
                echo "=========================================="
                #change swap the second parameter
                $1=$HEADREV  #<-- IS THIS CORRECT?
        fi
...[rest of program here]

I want to replace the first parameter with the latest revision number and leave the rest of the script untouched. So the question is: How to I change a function's parameter value from inside the function?

Answer 1

You could make use of the set builtin in order to change a positional parameter.

The following snippet changes the first positional parameter, i.e. $1, to something:

set -- "something" "${@:2}"

As an example, refer to the following:

echo "Original parameters: $@"
set -- "something" "${@:2}"
echo "Modified parameters: $@"

Assuming this was placed in a script called script, and was invoked by saying bash script foo bar baz, it'd output:

Original parameters: foo bar baz
Modified parameters: something bar baz

Quoting from help set:

set: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]

 Set or unset values of shell options and positional parameters.