csh idioms to check for environment variable existence?

问题

I've got a few csh scripts where I need to check that certain environment variables are set before I start doing stuff, so I do this sort of thing:

if ! $?STATE then
    echo "Need to set STATE"
    exit 1
endif

if ! $?DEST then
    echo "Need to set DEST"
    exit 1
endif

which is a lot of typing. Is there a more elegant idiom for checking whether or not an environment variable is already set?

Notes:

• This question is quite similar, but specifically asks about solutions in bash.
• I'm not looking for people to advise me to stay away from csh because it's cursed, scary, or bash is better. I'm specifically interested in a more elegant solution than what I'm using now.

回答1:

I think the way you're doing it (an if statement with a condition using the $?VAR syntax, which evaluates to 1 if the variable is set, and 0 otherwise) is probably the most idiomatic csh construct that does what you want.

回答2:

Try the following:

[ -z STATE ] && echo "Need to set STATE"

[ ! -z DEST  ] && echo "Need to set STATE"

来源：https://stackoverflow.com/questions/2336388/csh-idioms-to-check-for-environment-variable-existence