bashubuntu

Why does this bash script fail on ubuntu?

On ubuntu I run the following script (which should randomly fail or succeed for testing purposes):

if [ "$RANDOM" -gt 16384 ]; then
    echo "Success!"
    exit 0
else
    echo "Failure!"
    exit 1
fi

with

sh random.sh

but it fails with

random.sh: 1: [: Illegal number: 
Failure!

What is the cause of the problem?

Solution

  • The $RANDOM variable is a bash extension, so you have to invoke your script with bash instead of sh. On Ubuntu, sh is typically linked to the more light-weight dash shell which doesn't support these extensions.

    Also see Difference between sh and Bash

    To make reasonably sure that the correct interpreter is used, add a shebang to your script:

    #!/bin/bash

if [ "$RANDOM" -gt 16384 ]; then
    echo "Success!"
    exit 0
else
    echo "Failure!"
    exit 1
fi

    and make it executable:

    chmod +x random.sh

    A user can now simply execute the script without specifying what interpreter it needs in order to work properly:

    ./random.sh