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

I wrote this function...the concept is simple but hey I am a perl newbie, so it doesn't really work as intended. The function is supposed to be passed a path name, check to see if the file exists, and pipe the output from a cat function (of that file) to a new file (which is saved into a predetermined directory). Now, here is my broken function: 

sub find_files {
    my $file_name = shift;
    my $path = qx/pwd/;
    print $path;

    my $file = basename($file_name);

    open(my $FILE_H, '>', "$path/$file"); #||                         
+                                                                     
+                                          
          #  die "Unable to open file: $!";                           
+                                                                     
+                                          

    if(defined(qx/test -e $file_name; echo $?/)) {

        my $file_data = qx/cat $file_name/;
        print $FILE_H $file_data;
    } else {
        print "here";
        print $FILE_H "Unable to find file name: $file_name";
    }
    close($FILE_H);
}

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my @file_name_array = (
"/proc/cpuinfo", "/proc/meminfo", "/etc/fstab",
"/proc/net/pf_ring/info", "/var/log/boot.log",
"/etc/sysconfig/network-scripts/ifcfg-eth0",
"/etc/sysconfig/network-scripts/ifcfg-eth1",
"/etc/sysconfig/network-scripts/ifcfg-eth2",
"/etc/sysconfig/network-scripts/ifcfg-eth3",
"/etc/sysconfig/network-scripts/ifcfg-eth4",
"/etc/udev/rules.d/70-persistent-net.rules"
);

[download]

Replies are listed 'Best First'.
Re: Broken Function
by choroba (Cardinal) on Apr 04, 2014 at 13:21 UTC
    No need to call test to see if a file exists. We have -e in Perl, too. We even have File::Copy, so you don't need to cat a file. Path::Tiny wraps all the path related operations nicely: 
    #!/usr/bin/perl
# Untested!

use Path::Tiny;

my @files = ( ... );
sub find_files {
    my $filename = shift;
    my $path     = 'Path::Tiny'->cwd;
    my $file     = path($filename)->basename;
    if (-e $filename) {
        path($filename)->copy("$path/$file");
    } else {
        open my $OUT, '>', "$path/$file" or die $!;
        print {$OUT} "Unable to find $filename\n";
    }
}

    [download]

    Note that -e returns true for directories, too, so you might need a different test (-f maybe?). Also, you should check the return value of copy.

    لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
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      When you Path::Tiny, to spew is lovely ,fiend :) 
      else {
    path( "$path/$file" )->spew_utf8("Unable to find $filename\n");
}

      [download]
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Re: Broken Function
by Happy-the-monk (Canon) on Apr 04, 2014 at 13:22 UTC

    Perl has a -e test builtin, no need to use the shell's test function.

    But a -r test suggests itself if you need to read the file.

    If this is not just a fiddle-with-perl exercise, what you are doing is basically copying a file. You could shortcut all of it to use File::Basename qw(basename); use File::Copy qw(copy); copy $_[0], basename $_[0];

    Cheers, Sören

    Créateur des bugs mobiles - let loose once, run everywhere.
    (hooked on the Perl Programming language)

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Re: Broken Function
by BrowserUk (Patriarch) on Apr 04, 2014 at 13:22 UTC
    it doesn't really work as intended.

    That is a lousy error description.

    • What does it do that isn't intended?
    • And/or: What doesn't it do that is intended?
    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

      I get something like this: cat: /proc/cpuinfo: No such file or directory print() on closed filehandle $FILE_H at itworks.pl line 91. I am expecting my function to create a new file whether or not the file exists. But, my major hurdle is the second error message.

[reply]

        If you had not commented out your "or die "Could not open file: $!\n" code, then the reason why the file handle did not open would have been printed.

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