Re-reading from already read filehandle

perl filehandle
rajeev picture rajeev · Aug 20, 2012 · Viewed 25.2k times · Source

I opened a file to read from line by line:

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

Later on in the program, I try to re-read the file (walk thru the file again):

while (<FH>)
{
    # ...do something
}

and realized that it is as if the control within file is at the EOF and will not iterate from first line in the file.... is this default behavior? How to work around this? The file is big and I do not want to keep in memory as array. So is my only option is to close and open the file again?

Answer

William Pursell picture William Pursell · Aug 20, 2012

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;

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, and you should strive to arrange your program so that the seek is not necessary.

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