scripting- Ignoring a variable when undefined

Question

HP-UX *** B.11.31 U ia64 **** unlimited-user license Hello,

var1=abc var2=xyz touch $var1 $var2 $var3 

if the one of the variable is not set the command fails with

ksh: var3: parameter not set 

How do we make the command ignore the variable that is not set/defined and create the files for the variables that are defined. Without if loops. Just within the touch command. Thanks

Answer 1

You'd get that error message if you had turned the -u option either by invoking ksh as ksh -u or ksh -o nounset or by running set -u or set -o nounset.

touch $var1 $var2 $var3

is wrong anyway unless those variables are meant to contain lists of file patterns.

It should have been:

touch -- "$var1" "$var2" "$var3" 

Now, if you want to allow one of them to be empty and not pass it as an empty argument to touch in that case (and work around set -u), you'd write:

touch -- ${var1:+"$var1"} ${var2:+"$var2"} ${var3:+"$var3"} 

Another option is to do:

(IFS=; set -f +u; touch -- $var1 $var2 $var3) 

With IFS=, we disable word splitting, with set -f globbing, but we rely on the third side-effect of leaving variables unquoted: empty removal. (and we also disable nounset with set +u, all of that in a subshell only).

Answer 2

I doubt if you can do it just in a line, you can try something like this

validate_touch() { for value in "$@" do if [ ! -z "$value" ]; then touch $value;fi done } validate_touch new