What's a easy way to validate if input is a file location in G'MIC?

Software G'MIC
1

Let’s say I have C:\Users\User\Pictures\mypic.png as an argument, it should return 1. Now, if I have [0] or 4, then it returns 0.

Something like ${is_image_arg\ $1}, but with space in mind.

2

I’d say:

isfile(['{/$arg}'])

although this explicitely makes the OS to check if the filename exists (and if filenames with malicious names as [0] exists, then… potential troubles…).

But you see that the question is actually very difficult to answer : “Giving any kind of input string, tell me if that is a filename or not ?”
As filenames can be almost any kind of string…

3

So, then this question becomes on checking if it contains a file extension and is a valid file. I know isin() would help verify if it contains a file extension. I could use 0 => $1 in a separate command and extract extension.

4

Ok, I think this will work out, what can go wrong?

foo_test_command:
 is_file:=isfile(['"$*"'])
 0 => "$*"
 ext={-1,x}
 is_valid_ext:=isin('$ext','png','txt','gpl','pal','pdn')
 rm. u {$is_file&&$is_valid_ext}

This means I will have to create a new command to specifically open .pal file, but eh. Not too hard.