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Learning Perl, 6th Edition by Tom Phoenix, Randal L. Schwartz, brian d foy

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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.[303]

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 data file 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;

Notice that you don’t include $! in this die message, since you’re not reporting that the system refused a request in this case. Here’s an example of checking whether a file is being kept up-to-date. In this ...

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