til/shell/check-if-the-first-argument-is-given.md

Check If The First Argument Is Given

In a shell script, you may want to check if an argument was given. Each argument is referenced numerically with the $ prefix, so the first argument is $1. To check if the first argument is given, you can use the -z check.

if [ -z "$1" ]
  then
    echo "The first argument is missing"
    exit 1
fi

The -z checks if the argument is a zero-length string (so "" or undefined will be true). If it is missing, then we echo out a message and exit the script. This is how I might fashion a script that requires the first argument.

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