How to define a shell script with variable number of arguments?

Question

I would like to define a simple abbreviation of a call to gs (ghostscript) via a shell script. The first argument(s) give all the files that should be merged, the last one gives the name of the output file. Obviously, the following does not work (it's just for showing the goal):

#!/bin/sh gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOUTPUTFILE=$last $1 $2 ... 

How can this be done?

One would typically call this script via myscript infile1.pdf infile2.pdf ... outfile.pdf or myscript *.pdf outfile.pdf.

Answer 1

The bash variables $@ and $* expand into the list of command line arguments. Generally, you will want to use "$@" (that is, $@ surrounded by double quotes). This will do the right thing if someone passes your script an argument containing whitespace.

So if you had this in your script:

outputfile=$1 shift gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOUTPUTFILE=$outputfile "$@" 

And you called your script like this:

myscript out.pdf foo.ps bar.ps "another file.ps" 

This would expand to:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOUTPUTFILE=out.pdf foo.ps bar.ps "another file.ps" 

Read the "Special Parameters" section of the bash man page for more information.

Answer 2

To pass the output file as the last argument, use an array:

ARGS=("$@") # Get the last argument outputfile=${ARGS[-1]} # Drop it from the array unset ARGS[${#ARGS[@]}-1]  exec gs ... -sOUTPUTFILE=$outputfile "${ARGS[@]}" 

Before version 4, bash didn't allow negative subscripts in arrays (and produced the error reported by Marius in the comments), so if you're using 3.x you need to use the much uglier

outputfile=${ARGS[${#ARGS[@]}-1]} 

This works for bash 4.x as well.