Default values to a unix shell script?

Question

Normally when a parameter is passed to a shell script, the value goes into ${1} for the first paramater, ${2} for the second, etc.

How can I set the default values for these parameters, so if no parameter is passed to the script, we can use a default value for ${1}?

Answer 1

You can't, but you can assign to a local variable like this: ${parameter:-word} or use the same construct in the place you need $1. this menas use word if _paramater is null or unset

Note, this works in bash, check your shell for the syntax of default values

Answer 2

You could consider:

set -- "${1:-'default for 1'}" "${2:-'default 2'}" "${3:-'default 3'}"

The rest of the script can use $1, $2, $3 without further checking.

Note: this does not work well if you can have an indeterminate list of files at the end of your arguments; it works well when you can have only zero to three arguments.