What does if( -f ) in Perl do?

Question

I came across this line of code:

if( -f  ) { ... }

-f appears to test whether the filename exists or not, but I am

Answer 1

In Unix, directories can contain the following types of files:

• Plain (what you would consider a file)
• Directory
• Named pipe
• Named socket
• ...

-f tests if the provided name references a file that's a plain file. It will return undef (error ENOENT) if the file doesn't exist, or some other false values if the file exists but it's not plain file (e.g. if it's a directory).

-X operators