Check if a filw is immutable for a certain amount of time

You can use flock to lock and check for locks.... but it will not kill anything, it can wait for a limited time if you whish.
The script supplied runs when the lock is acquired, that lock should kill itself to free the lock.


From man flock

NAME
       flock - manage locks from shell scripts

SYNOPSIS
       flock [options] file|directory command [arguments]
       flock [options] file|directory -c command
       flock [options] number

DESCRIPTION
       This utility manages flock(2) locks from within shell scripts or from the command line.

       The  first  and second of the above forms wrap the lock around the execution of a command, in a manner similar to su(1) or new-
       grp(1).  They lock a specified file or directory, which is created (assuming appropriate permissions) if it  does  not  already
       exist.  By default, if the lock cannot be immediately acquired, flock waits until the lock is available.

       The third form uses an open file by its file descriptor number.  See the examples below for how that can be used.

flock can do this for you. I expect you are using it already, but perhaps you are using something else to make the file immutable. You need to wrap the script's top-level commands in a main() function (any name will do) (top-level means not in a function already). You do it like this (no file locking yet)

#!/bin/sh
main()
{
  # top-level logic goes here
}
# Start the show
main "$@"

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Note that the last line of your script invokes main. You can define other functions in any order you choose and they can call each other, because [ba]sh has read them all in before trying to execute any of them.
To run your script with the file locked, change the last line and add error handling

# Start the show
flock -w 30 -E 4 "/scripts/test.file" main "$@"
retcod=$? # Capture return code from main (if flock succeeded) else 4 from flock
[ $retcod -ne 4 ] || { echo "Timed out waiting for lock" >&2; exit 1; }
# Check retcod for other errors here if you wish

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Error code 4 is an arbitrary choice. You want to use a number that main() cannot return

Oops - the above solution doesn't work: flock can't execute main (new shell process).
Never mind, you just need to have 2 scripts: one with flock and the second executed by flock

Thank you both, You helped me with my script a lot :)