Extracting an appimage on the wrong platform

[tresf]

For those interested, I wrote (with help) a very small script to help extract the contents of an AppImage when --appimage-extract is broken. This can happen when...

• The .AppImage file was compiled for another architecture (e.g. ARM64)
• You're not on Linux at all (e.g. macOS)
• This could also be used on Windows using WSL

https://github.com/tresf/appimage-extract

Usage:

git clone https://github.com/tresf/appimage-extract && cd appimage-extract
./appimage-extract.sh lmms-1.3.0-alpha.version-linux-arm64.AppImage

Purpose:

Working on #7252 I've been switching OSs and architectures a lot, so this tool allows me to inspect the structure of the AppImage without having the same platform that it was built for.

How it works:

It reads the ELF headers using either python3 or readelf to calculate the byte offset of the payload and then passes that value to unsquashfs.