Re: tail a file in perl

Here is a piece of code that I've written to get the last lines in a file for one of my programs:

my @lines;
my $currLine = 0;
my $maxLines = 10;

# Go through the file, saving the last $maxLines
while (<>){
    $lines[$currLine] = $_;
    $currLine++;
    $currLine = 0 if ($currLine == $maxLines);
}

# Print out the last $maxLines
for (1..$maxLines){
    print $lines[$currLine];
    $currLine++;
    $currLine = 0 if ($currLine == $maxLines);
}
[download]

I think this code is simple enough to understand what is going on, but if you need to explain more I will. (I have to get some real work done first ;)

Comment on Re: tail a file in perl Download Code

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Re: Re: tail a file in perl by blokhead (Monsignor) on Oct 23, 2002 at 17:22 UTC
Or a slightly more Perl-flavored version of your C-flavored code: `my @lines; my $maxlines = 10; while (<>) { push @lines, $_; shift @lines if (@lines > $maxlines); } print join("\n", @lines) . "\n";` [download] Instead of using a circular array, this uses `@lines` as a FIFO buffer, storing the last `$maxlines` lines, using `push` and `shift`. Much less code! I'm not sure if this is the way it's implemented in the aforementioned perlfaq5 and other discussions... Update: The solutions here using `seek` to read blocks starting at the end are going to be more efficient than this one (as the whole file is not read), although this solution is fine for reasonable-sized files.. Plus I think it's much simpler to comprehend. blokhead	[reply] [d/l] [select]

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Re: Re: tail a file in perl
by blokhead (Monsignor) on Oct 23, 2002 at 17:22 UTC

my @lines;
my $maxlines = 10;
while (<>) {
    push @lines, $_;
    shift @lines if (@lines > $maxlines);
}
print join("\n", @lines) . "\n";
[download]

@lines

$maxlines

push

shift

Update: The solutions here using seek to read blocks starting at the end are going to be more efficient than this one (as the whole file is not read), although this solution is fine for reasonable-sized files.. Plus I think it's much simpler to comprehend.

blokhead

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