Bash : How to create a Bash script that has the ability to update itself?

Goal : Create a bash script that can update itself

Example

./my-script.sh 
 $ Hello world

Then when supplied with argument to update itself

./my-script.sh --update

./my-script.sh
$ Hello World Updated!

Problem : Unable to update script while loaded in memory

Things I've tried

#!/bin/bash

function update {
 
 urlOfUpdatedVersion="..."
 existingScriptLocation = "..."
 myLocalPath="..."

 wget $urlOfUpdatedVersion > $myLocalPath/my-script.sh

 mv myLocalPath/my-script.sh $existingScriptLocation
}

if [[ "$1" == "--update" ]]; then
 update
fi

echo "Hello World"

For sake of simplicity assume the updated script that gets pull down from the 'wget' is the exact same but with the following echo update

echo "Hello World Updated"

Solution

Updating a script while its running can be hard because the script is already loaded in memory, so it can be difficult to modify it directly. But you can use a turnaround for this.

First: Create a temporary script to handle the update
Second: Download the new version of the script
Third: Replace the original script with the new version
Finally: You run the new updated script

Here is an example of how I would apply this :

#!/bin/bash

function update {
    urlOfUpdatedVersion="https://example.com/path/to/updated-script.sh"
    existingScriptLocation="$(realpath "$0")"
    tempScriptLocation="/tmp/my-script.sh"

    # Download the updated version to a temporary location
    wget -q -O "$tempScriptLocation" "$urlOfUpdatedVersion"

    # Replace the current script with the updated version
    if [[ -f "$tempScriptLocation" ]]; then
        mv "$tempScriptLocation" "$existingScriptLocation"
        chmod +x "$existingScriptLocation"
        echo "Script updated successfully."

        # Optionally, you can run the updated script
        exec "$existingScriptLocation"
    else
        echo "Failed to download the updated script."
        exit 1
    fi
}

if [[ "$1" == "--update" ]]; then
    update
    exit 0
fi

echo "Hello World"