linux shell script with if and shopt [duplicate]

Question

I've written the following shell script:

#!/bin/bash
...
#delete downloaded file

if [ "$param" == "delete" ]; then

    shopt -s extglob
    cd $DataPersistent/download/
    rm -f !($label.*)
    cd $DataPersistent/swm/install_pkg/
    rm -rf !($label|$label.json|active.json)
    shopt -u extglob
fi
...

When I remove the if statement, it works fine, but when I add the if statement, it results in the following error:

/usr/local/bin/clear.sh: line 17: syntax error near unexpected token `('
/usr/local/bin/clear.sh: line 17: `    rm -f !($label.*)'

What's causing this? How can I fix it?

Answer 1

shopt -s extglob changes the syntax of the shell. Without this statement, the extended globbing pattern !($label|$label.json|active.json) is invalid syntax.

The issue is that before the shell executes the shopt command enabling the extglob shell option, the whole if statement is already parsed, and the syntax error found.

When the line that require the change in allowed syntax is not part of a compound command (which is what the if statement is), the shopt command has already enabled extglob, which is why it works.

To solve this, enable extglob before the if statement, and disable it afterwards.

This is the same issue as also found here: Setting bash options in a compound command