in reply to User Who Modified File

What do you mean by "file"? Just a file on a (Unix-like) filesystem? If so, Perl's stat function returns a whole bunch of statistics on files, including the numeric user ID of the file's owner. The getpwuid function can convert that to the user name.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In Section Seekers of Perl Wisdom