Re: Unix ls -lrt | tail -1 in Perl
Sudarshan Raghavan wrote:
>
> On Fri, 21 Mar 2003, NYIMI Jose (BMB) wrote:
>
> > > From: Palmer Greg [mailto:[EMAIL PROTECTED]
> > >
> > > $filename = `ls -ltr|tail -1 $DIRECTORY`;
> > > print $filename;
> >
> > Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
> >
> > my $latest = (sort {-M $a <=> -M $b} <$dir/*>)[0];
> > Will be my way to go, thanks Sudarshan Raghavan
>
> The above solution will work but a more time effecient way will be to use
> the Schwartzian transform as explained by Rob Hanson in his mail. Thanks
> Rob :-)
>
> The solution using while that I posted is also more time effecient than my
> sort solution :-)
If you want efficiency then don't use sort at all. This was about three
to four times faster on my cursory tests then then Rob's example and
about two to three times faster than using `ls -ltr|tail -1` from within
perl.
my $latest;
opendir my $dh, $dir or die "Cannot open $dir: $!";
my $t = ~0;
while ( defined( my $file = readdir $dh ) ) {
if ( -f "$dir/$file" and -M _ < $t ) {
$latest = $file;
$t = -M _;
}
}
print "$latest\n";
John
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RE: Unix ls -lrt | tail -1 in Perl
On Fri, 21 Mar 2003, NYIMI Jose (BMB) wrote:
> > -Original Message-
> > From: Palmer Greg [mailto:[EMAIL PROTECTED]
> > Sent: Thursday, March 20, 2003 4:50 PM
> > To: NYIMI Jose (BMB)
> > Subject: RE: Unix ls -lrt | tail -1 in Perl
> >
> >
> > $filename = `ls -ltr|tail -1 $DIRECTORY`;
> > print $filename;
>
> Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
>
> my $latest = (sort {-M $a <=> -M $b} <$dir/*>)[0];
> Will be my way to go, thanks Sudarshan Raghavan
>
> José.
The above solution will work but a more time effecient way will be to use
the Schwartzian transform as explained by Rob Hanson in his mail. Thanks
Rob :-)
The solution using while that I posted is also more time effecient than my
sort solution :-)
hth
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RE: Unix ls -lrt | tail -1 in Perl
> -Original Message-
> From: Palmer Greg [mailto:[EMAIL PROTECTED]
> Sent: Thursday, March 20, 2003 4:50 PM
> To: NYIMI Jose (BMB)
> Subject: RE: Unix ls -lrt | tail -1 in Perl
>
>
> $filename = `ls -ltr|tail -1 $DIRECTORY`;
> print $filename;
Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
my $latest = (sort {-M $a <=> -M $b} <$dir/*>)[0];
Will be my way to go, thanks Sudarshan Raghavan
José.
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RE: Unix ls -lrt | tail -1 in Perl
If you use the first version that Sudarshan posted, you might want to use
this instead. It uses map, and is a lot faster.
my $latest = (sort {$b->{mtime} <=> $a->{mtime}}
map {{mtime => -M $_, file => $_}}
<$dir/*>)[-1];
print $latest->{file}, "\n";
Benchmark results with and without using map:
Benchmark: timing 100 iterations of No-MAP, With-MAP...
No-MAP: 13 wallclock secs ( 2.43 usr 6.43 sys + 4.00 cusr 1.41 csys =
0.00 CPU)
With-MAP: 8 wallclock secs ( 1.57 usr 0.81 sys + 4.04 cusr 1.27 csys =
0.00 CPU)
Using map allows -M to be performed on each file only once (instead of once
per sort iteration). And since this is an expensive operation doing it only
once will save a lot of CPU time.
Rob
-Original Message-
From: Sudarshan Raghavan [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 20, 2003 9:17 AM
To: Perl beginners
Subject: Re: Unix ls -lrt | tail -1 in Perl
On Thu, 20 Mar 2003, NYIMI Jose (BMB) wrote:
> Hello,
>
> How can I do this unix command in Perl ? : ls -lrt | tail -1
> Actually, i would like to get the most recent file from a given directory.
my $latest = (sort {-M $b <=> -M $a} <$dir/*>)[-1];
or
my $latest;
while (<$dir/*>) {
$latest = (defined ($latest) && (-M $_ > -M $latest)) ? $latest : $_;
}
Remember to check for the definedness of $latest if $dir is an empty
directory
>
> Thanks in advance for your input.
>
> José.
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Re: Unix ls -lrt | tail -1 in Perl
On Thu, 20 Mar 2003, NYIMI Jose (BMB) wrote:
> Hello,
>
> How can I do this unix command in Perl ? : ls -lrt | tail -1
> Actually, i would like to get the most recent file from a given directory.
my $latest = (sort {-M $b <=> -M $a} <$dir/*>)[-1];
or
my $latest;
while (<$dir/*>) {
$latest = (defined ($latest) && (-M $_ > -M $latest)) ? $latest : $_;
}
Remember to check for the definedness of $latest if $dir is an empty
directory
>
> Thanks in advance for your input.
>
> José.
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