Under *nix, ctime is not creation time, but actually the last time the inode for the file was changed (from man stat - Last file status change time). MTime is the last modification time. As was said by kennethk in Re: File test to see creation time rather than last modified time, *nix does not record creation time of a document. An inode may change at some unexpected times (for example, when the mtime is changed).

ls also lists the -c option as

Use time of last modification of the inode (file created, mode changed, etc.) for sorting (-t) or printing (-l (ell))

I have seen the c in ctime being misunderstood for the 15-20 years I have been using *nix. In my tenure, this misunderstanding has been the cause of many mistakes on interpreting data from the filesystem.

You could use stat():

if ( (time - (stat FILE)[10]) / (60*60*24) > 5 ) { ... }
[download]

Actually, as -M is "Script start time minus file modification time, in days", you'd have to store the return value of time() right at the beginning of the script, to get the exact equivalent for ctime... though I suppose the difference would be negligible.   (Update: actually (RTFM :) — use "perldoc -f -X" to get the docs for the filetests...) there even seems to be an option -C which does just that...)

Alternatively (Update2: and preferably — see kenneth/MidLifeXis's comments below), reset the modification time to what it was before, every time you make a modification...