I am trying to append a path to the end of my PERL5LIB environment variable, but I am not sure that this variable will always exist. If it doesn't exist I would like to simply initialize it to the value that I am trying to append.

Here is an example that works:

if ( $?PERL5LIB ) then setenv PERL5LIB ${PERL5LIB}:/some/other/path else setenv PERL5LIB /some/other/path endif 

While this works, it still seems pretty clunky since I have to basically write the same line twice. What I would like to do is come up with a more efficient one line solution (possibly using parameter expansion).

Is there a way to consolidate this to one line? (Or a couple lines that don't involve writing out "/some/other/path" multiple times)

For example this could be done in bash:

export PERL5LIB=${PERL5LIB:+${PERL5LIB}:}/some/other/path 

2 Answers

If the environment variable is not defined, set it to an empty string. This avoids duplication.

if ( ! $?PERL5LIB ) then setenv PERL5LIB "" else setenv PERL5LIB "${PERL5LIB}:" endif setenv PERL5LIB ${PERL5LIB}/some/other/path 

For lack of a better answer I will post a slightly improved version of what I had in the question. The following at least eliminates writing out the path twice...

set perl5lib = "/some/other/path" if ( $?PERL5LIB ) then setenv PERL5LIB ${PERL5LIB}:${perl5lib} else setenv PERL5LIB ${perl5lib} endif 

Although it's only a very slight improvement, at least it's something.

EDIT:

Technically this could be shortened to:

set perl5lib = "/some/other/path" [ $?PERL5LIB ] && setenv PERL5LIB ${PERL5LIB}:${perl5lib} || setenv PERL5LIB ${perl5lib} 

Not the most readable, but I guess that's about as good as I'm going to get.

EDIT 2:

Possibly more readable? ...I don't really know.

set perl5lib = "/some/other/path" [ $?PERL5LIB ] \ && setenv PERL5LIB ${PERL5LIB}:${perl5lib} \ || setenv PERL5LIB ${perl5lib}