Re-reading from already read filehandle

Question

I opened a file to read from line by line:

open(FH,\"<\",\"$myfile\") or die \"could not open $myfile: $!\";
while ()
{
    # ...do something
}
         


        

Answer 1

Use seek to rewind to the beginning of the file:

seek FH, 0, 0;

Or, being more verbose:

use Fcntl;
seek FH, 0, SEEK_SET;

Please note that it greatly limits the usefulness of your tool if you must seek on the input, as it can never be used as a filter. It is extremely useful to be able to read from a pipe. Keeping in mind that 57% of all statistics are made up, you should realize that 98% of programs that seek on their input do so needlessly. Try very hard to process your data in such a way that you don't need to read it twice. If that is possible, your program will be much more useful.

Answer 2

You have a few options.

• Reopen the file handle
• Set the position to the beginning of the file using seek, as William Pursell suggested.
• Use a module such as Tie::File, which lets you read the file as an array, without loading it into memory.