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How to goto new sub if file empty?

by Anonymous Monk
on Apr 23, 2003 at 05:19 UTC ( #252453=perlquestion: print w/replies, xml ) Need Help??

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hey everyone :)

I am very new to Perl and can't understand why I can't check to see if a file is empty in a while loop...

I am building a page for my teacher to be able to change links on a school site anytime he wants through his browers. My script opens a file, reads the lines, splits the contents of the line into an array and displays them (not like you don't understand this already... don't mean to offend any of you :) )

Anyway, if the file is empty, I am trying to redirect to a subroutine called stopit..

open(FILE, "links.dat") || die "Can't open file!"; flock(FILE, 2) || die "Can't lock file!"; while ($line = <FILE>) { chomp $line; my @part = split(/\|/,$line); if ($part[0] eq "") { &stopit; } if ($part[3] eq "new") { $which = " target=\"_blank\""; } print "<li><a href=\"$part[2]\"$which>$part[1]</a></li><br>\n"; } close(FILE); print "</ul></body></html>"; sub stopit { close(FILE); print "There are currently no links :("; exit; }

What am I doing wrong? I thought I could check to see if the first part of the array has a value near the beginning og the while loop?

I know the coding is very crude... please be gentle!!

Replies are listed 'Best First'.
Re: How to goto new sub if file empty?
by pfaut (Priest) on Apr 23, 2003 at 05:25 UTC

    If the file is empty, the first attempt to read from it returns false (undef) and you never execute the body of the while loop. Your call of &stopit is inside that body so it never gets called. You can check for an empty file with eof before executing the while.

    open(FILE, "links.dat") || die "Can't open file!"; flock(FILE, 2) || die "Can't lock file!"; stopit if eof FILE; while ($line = <FILE>) { ....
    90% of every Perl application is already written.
    dragonchild
      Thanks a million pfaut!

      That was exactlly what I was trying to figure out... how to check for content in the file before I assigned it to a variable and started a loop :)

      Thanks again!!

Re: How to goto new sub if file empty?
by robartes (Priest) on Apr 23, 2003 at 05:55 UTC
    Another way of checking the emptiness of a file, without even opening it, is using the -z filetest operator:
    stopit() if -z $file;

    CU
    Robartes-

Re: How to goto new sub if file empty?
by vek (Prior) on Apr 23, 2003 at 06:07 UTC
    Something else you could try is a file test before attempting to open the file:
    if (-s $file) { open(FILE, $file) || die "open: $file - $!\n"; # etc } else { warn "There are currently no links :(\n"; # or similar msg exit(); }
    Take a peek at this for a list of file test operators.

    -- vek --
Re: How to goto new sub if file empty?
by Anonymous Monk on Apr 23, 2003 at 07:32 UTC
    Wow, thanks to everyone for all your help!!!

    Got it working perfect!

    robj :)

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