(or "In dash, ... are not supported." when using
# Open FD #10 for writing exec 10> file
Either rewrite the script to only use FDs in the valid range, or switch to a shell that allows a larger range like
The shell grammar is only required to recognize a single digit before redirections to set the file descriptor, which limits the portable range to 0-9.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.