What am I doing wrong?

• Your glob may not match any files
• Your script may not be opening any matched files
• Your grep regex may not match what you want it to
• Your unlink may be failling

That's just 4 possibilities and you won't know which is the real problem until you add some diagnostics to your script. eg (untested):

use strict;
use warnings;

while ( my $file = glob '*.txt' ) { 

    print "Debug: found file $file\n";
    open my $fh, '<', $file or die "Cannot open file $file: $!";
    my $headers = grep /^>/, <$fh>;

    if ($headers <= 3) {
        unlink $file or die "Cannot unlink file $file: $!";
    } else {
        print "Debug: file $file only has $headers headers - skipping\
+n";
    }
}
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But I get this error:

Debug: found file 1.txt

Debug: file 1.txt only has 4 headers - skipping

Debug: found file 2.txt

Cannot unlink file 2.txt: Permission denied at 1.pl line 11, <$fh> line 6.

Hello abhikalrt53,

You need to close the filehandle before you can unlink the file:

...
open my $fh, '<', $file or die "Cannot open file $file: $!";
my $headers = grep /^>/, <$fh>;
close $fh or die "Cannot close file $file: $!";

if ($headers <= 3) {
    unlink ...
[download]

Hope that helps,

Athanasius <°(((>< contra mundum

Iustus alius egestas vitae, eros Piratica,

that's what your regex does, its not counting all > in the file.

Debugging hints :

• try dumping what $headers holds.
• put sample data after __DATA__ and use DATA as file handle

Use tr instead of grep to count the '>' in a string.

Update: or use the command line grep instead:

Update: Nevermind ;)

I can imagine how to use tr/// instead of m//, but how do you want to replace grep with tr?

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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tr/// returns the number of substitutions made, i.e. 0 (or false) if the searched character wasn't found, and something true otherwise. So it could more or less work to replace a grep in the specific use of grep in the original post, but you can't use a regex to specify that the ">" character should be at the beginning of the line.

Depends.

qwurx [shmem] ~> touch foo.txt
qwurx [shmem] ~> perl -Mautodie=open,unlink -le '$_=pop;open "<", $_; 
+unlink $_' foo.txt
qwurx [shmem] ~> ls foo.txt
ls: cannot access foo.txt: No such file or directory
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AFAIK...

• Linux: Unlinking a file doesn't break the relation between an open file handle and the file system space allocated for the file; nor does holding an open file handle prevent unlink from succeeding, which is a directory related operation. The file's blocks are open to reallocation after the last reference to the file container is gone
• Windows: Can't delete a busy file (the OS is aware of open file handles pointing to it)
perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

Depends....

Yes, there exist differences between the platforms

And yes, the portable practice is preferable because it is portable

And yes, error checking will let you know if there are errors