Question

Possible Duplicate:
Ternary operator (?:) in Bash

If this were AS3 or Java, I would do the following:

fileName = dirName + "/" + (useDefault ? defaultName : customName) + ".txt";

But in shell, that seems needlessly complicated, requiring several lines of code, as well as quite a bit of repeated code.

if [ $useDefault ]; then
    fileName="$dirName/$defaultName.txt"
else
    fileName="$dirName/$customName.txt"
fi

You could compress that all into one line, but that sacrifices clarity immensely.

Is there any better way of writing an inline if with variable assignment in shell?

Answer 1

There is no ?: conditional operator in the shell, but you could make the code a little less redundant like this:

if [ $useDefault ]; then
    tmpname="$defaultName"
else
    tmpname="$customName"
fi
fileName="$dirName/$tmpname.txt"

Or you could write your own shell function that acts like the ?: operator:

cond() {
    if [ "$1" ] ; then
        echo "$2"
    else
        echo "$3"
    fi
}

fileName="$dirname/$(cond "$useDefault" "$defaultName" "$customName").txt"

though that’s probably overkill (and it evaluates all three arguments).

Thanks to Gordon Davisson for pointing out in comments that quotes nest within $(...).