I'm looking to set the value of a variable to one thing if it was already set or another if it was not. Here's an example of what I mean
export RESULT=${VALID:+Yes:-No}
Where the value of ${VALID:+Yes:-No} would be Yes if the variable was set or No if it was not.
One way I can do it now:
if [ -n "${VALID}" ]; then
export RESULT=Yes
else
export RESULT=No
fi
I could do it like this, but it would be nice to have a "one-liner".
Is it possible to do this in one line?
There's no way to do multiple parameter expansions within one variable assignement.
Without using an if statement, you can just use a couple of parameter expansions.
$ VALID="aaa"
$ RESULT="${VALID:+Yes}"; RESULT="${RESULT:-No}"; echo $RESULT
Yes
$ VALID=""
$ RESULT="${VALID:+Yes}"; RESULT="${RESULT:-No}"; echo $RESULT
No
It's not a single statement, but it's short enough that it fits on one line without the complexity of a subshell and if.
You can use an array with 2 elements (no yes) and based on variable's length decide which value to be returned:
# variable set case
>>> VALID=foo
>>> arr=(no yes) && echo "${arr[$((${#VALID} > 0))]}"
yes
# variable not set
>>> unset VALID
>>> arr=(no yes) && echo "${arr[$((${#VALID} > 0))]}"
no
The -v VAR printf option is a bash extension. Without it, you could use command substitution. (Variable names deliberately down-cased.)
printf -v result %.3s ${valid:+YES}NO
One line, requirement met:
export RESULT=$([ -n "$VALID" ] && echo Yes || echo No)
...&&...||... construct, you may as well just write [ -n "$VALID" ] && export RESULT=Yes || export RESULT=No.
${${VALID:+Yes}:-No}.