if -s clause on a FILEHANDLE

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

I am running a system command to a file passing the data to a filehandle, but the if clause does not work. My goal is to run a system app command and if it creates a file greater than 0 bytes then use MIME:Lite to email the data otherwise just "touch" a file.Any ideas? thank you!

## Set pragmas

        use strict;

        my $foreigntapes="/usr/local/log/foreign_tapes.log";
        delete $ENV{'IFS'};
        local $ENV{'PATH'}= "/usr/epoch/bin:/usr/epoch/EB/bin:/usr/bin
+:/usr/sbin:/bin:/sbin";

        open (OUT, ">$foreigntapes") || die "could not open file:$!";
        my @ftapes = grep s/^barcode=//, `evmvol -w label_state=1`;
        my $svsel = select; select OUT; $| = 1;
        print OUT "@ftapes";
        if ( -s OUT ) {
                     print "file is greater than 0 bytes \n";
        }
[download]

Comment on if -s clause on a FILEHANDLE Download Code

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Re: if -s clause on a FILEHANDLE by Fletch (Bishop) on Jun 08, 2004 at 14:06 UTC
Erm, why not just `if( @ftapes ) { ... }`? Update: Also note that since you call `select OUT` and never re-`select` the old handle that your `print` will go to the `OUT` handle. You may want to use the common `select( (select(OUT),$\|=1)[0] )` idiom instead.	[reply] [d/l] [select]
Re^2: if -s clause on a FILEHANDLE by drock (Beadle) on Jun 08, 2004 at 14:24 UTC
what exactly is `select( (select(OUT),$\|=1)[0] )` [download] saying? I still want to state `if ( -s "@ftapes" ) { ..... }` [download] right? not just if ( "@ftapes" )	[reply] [d/l] [select]
Re^3: if -s clause on a FILEHANDLE by Fletch (Bishop) on Jun 08, 2004 at 14:42 UTC
The select stuff is a hackish shortcut from the dawn of time (or at lest the perl4 days) to set autoflush on a handle without changing the current default output handle afterwards. The chunk inside the inner parens is a list consisting of the previous default output handle (what you were getting with `my $svsel = select OUT;`) and then setting `$\|` on the default output handle (which is then `OUT` since the `select` executes first). The list value is subscripted to get just the first element (the old saved handle) and that's passed to `select` to reset the default output handle. And no, you don't want `-s "@ftapes"`. `-s` gets the size of a file (either by name or for an already opened filehandle). Yours would attempt to find the size of a file named after the contents of `@ftapes` joined by `$,`. Using an array in a scalar context evaluates to the number of items in the array; if you found any items then `@ftapes` will have a non-zero number of elements and evaluate to a true boolean value.	[reply] [d/l] [select]
Re^4: if -s clause on a FILEHANDLE by drock (Beadle) on Jun 08, 2004 at 21:43 UTC
Re: if -s clause on a FILEHANDLE by pelagic (Priest) on Jun 08, 2004 at 13:57 UTC
Close the file before asking it's properties. pelagic	[reply]
Re^2: if -s clause on a FILEHANDLE by Fletch (Bishop) on Jun 08, 2004 at 14:47 UTC
You don't have to close it, but you do need to make sure that any writes that you want considered have been flushed (either by setting `$\|`, calling `$fh->flush`, or closing it if you really are done).</pedant>	[reply] [d/l] [select]
Re: if -s clause on a FILEHANDLE by BrowserUk (Patriarch) on Jun 08, 2004 at 14:45 UTC
If you want to know how much was written prior to closing the file, use tell to tell you :) `print OUT "@ftapes"; if( tell( OUT ) ) { ... }` [download] Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail	[reply] [d/l]