Re^2: when reading a file how to print a line one above the current line??

But why tell him to read a filename at all in the case? I find that if one is taking filenames on the commandline, it's much better to use the diamond operator and let perl decide whether I should be reading from a bunch of files or STDIN, which allows for more flexibility.

And some technical critique - you didn't guard your print $last. This is what I have in mind:

#!/usr/bin/perl
use strict;
use warnings;

my $prevline;
while (<>) {
    if(/ALARM:/) {
        print $. - 1, ": $prevline" if defined $prevline;
        print "$.: $_";
    }
    $prevline = $_;
}
[download]

____________
Makeshifts last the longest.

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Re: Re^2: when reading a file how to print a line one above the current line?? by dsheroh (Monsignor) on Jun 04, 2002 at 17:10 UTC
Good point, but, personally, I'd do it as `my $prevline = ''; ... print $. - 1, ": $prevline";` [download] This way doesn't have the overhead of testing every time whether `$prevline` is defined. Or you could initialize it to "BOF\n" for a more explicit indication of what's going on.	[reply] [d/l] [select]
Re^4: when reading a file how to print a line one above the current line?? by Aristotle (Chancellor) on Jun 05, 2002 at 06:06 UTC
I thought about the efficiency issue, but I guess it boils down to personal choice. With the guarded print you don't get to see a `-1:\n` should the pattern happen to match on the first line, and really that single test does very little to performance. We could pull out Benchmark here but I suspect the difference would be within measurement jitter (how is this exactly called in English?) for any less than a few hundred thousand lines. Makeshifts last the longest.	[reply]