How to build a conditional while statement in Bash?

Hello Stackoverflow community,

In order to make my code as less ‘copy-paste-ey’ as possible, I’m trying to come up with a smarter method to make it more compact.

Is there any way to create a ‘conditional while’-statement (if that’s even a thing) in your script without having to repeat everything over again? Basically, I have the same core function, but a different while statement should be fired off depending if a variable is present or not.

See my original script below:

messenger() {
msg1=$1
count=0
echo " "
while [[ $count -ne ${#1} ]]
do
    echo -n "*"
    ((count += 1))
done
echo -e "n$1"
while [[ $count -ne 0 ]]
do
    echo -n "*"
    ((count -= 1))
done
echo -e "n"
}

This is my core function, but instead of counting the lenght of $1, I’d like the possibility for the count to be equal to the provided variable $val, but only if it’s provided.

What I’d like to achieve – but doesn’t work due to the syntax:

messenger() {
msg1=$1
val=$2
count=0
echo " "
if [[ -z $val ]]
then
   while [[ $count -ne ${#1} ]]
else
   while [[ $count -ne $val ]]
fi
do
    echo -n "*"
    ((count += 1))
done
echo -e "n$1"
while [[ $count -ne 0 ]]
do
    echo -n "*"
    ((count -= 1))
done
echo -e "n"
}

The only way I manage to achieve is by reusing most of the core, basically a copy-paste action. I’d like to come up with a better method of achieving this:

messenger() {
msg1=$1
val=$2
count=0
echo " "
if [[ -z $val ]]
  then
        while [[ $count -ne ${#1} ]]
        do
            echo -n "*"
            ((count += 1))
        done
        echo -e "n$1"
        while [[ $count -ne 0 ]]
        do
            echo -n "*"
            ((count -= 1))
        done
        echo -e "n"
else
        while [[ $count -ne $val ]]
        do
            echo -n "*"
            ((count += 1))
        done
        echo -e "n$1"
        while [[ $count -ne 0 ]]
        do
            echo -n "*"
            ((count -= 1))
        done
        echo -e "n"
fi
}

I believe this example perfectly sums up what I’m trying to achieve. If you can point me towards a direction, I would really appreciate it.

$ bash --version
GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)

Thank you in advance,

Ivan

Answer

Use the default value operator.

while [[ $count -ne ${val:-${#1}} ]]

If val is not empty, you’ll use that value. Otherwise, it will use ${#1}.