http://qs321.pair.com?node_id=252453

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;
}

[download]

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>) {
....

    [download]
    90% of every Perl application is already written. ⇒
    dragonchild
[reply]
[d/l]
      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!!

[reply]
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;

    [download]

    CU
    Robartes-

[reply]
[d/l]
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();
}

    [download]
    Take a peek at this for a list of file test operators.

    -- vek --
[reply]
[d/l]
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 :)

[reply]

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