Learning Perl, 8th Edition

Chapter 12. File Tests

Earlier, we showed you how to open a filehandle for output. Normally, that creates a new file, wiping out any existing file with the same name. Perhaps you want to check that there isn’t a file by that name. Perhaps you need to know how old a given file is. Or perhaps you want to go through a list of files to find which ones are larger than a certain number of bytes and have not been accessed for a certain amount of time. Perl has a complete set of tests you can use to find out information about files.

File Test Operators

Perl has a set of file test operators that let you get particular information about files. They all take the form of -X, where the X represents the particular test (and there is a literal -X file test operator too, to confuse things a bit). In most cases, these operators return true or false. Although we call these things operators, you’ll find their documentation in perlfunc.

Note

To get the list, use the command line perldoc -f -X. That -X is literal and not a command-line switch. It stands in for all the file test operators since you can’t use perldoc to look them up individually.

Before you start a program that creates a new file, you might want to ensure that the file doesn’t already exist so that you don’t accidentally overwrite a vital spreadsheet datafile or that important birthday calendar. For this, you can use the -e file test, testing a filename for existence:

die "Oops! A file called '$filename' already exists.\n" if -e $filename; ...