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Re: Reading the contents of a file from the bottom up

by roboticus (Chancellor)
on Nov 24, 2019 at 20:28 UTC ( #11109156=note: print w/replies, xml ) Need Help??


in reply to Reading the contents of a file from the bottom up

Scotmonk:

If the file is small enough that it fits comfortably in memory, you could just read the whole thing and then reverse it, like this:

# foo.pl - print a file in reverse use strict; use warnings; my $FName = shift // die "Expected a filename!"; open my $FH, '<', $FName or die "Can't open $FName: $!\n"; # Read all the lines my @lines = <$FH>; # Reverse the order @lines = reverse @lines; for my $line (@lines) { print $line; }

When I run it on itself, I get:

$ perl foo.pl foo.pl } print $line; for my $line (@lines) { @lines = reverse @lines; # Reverse the order my @lines = <$FH>; # Read all the lines open my $FH, '<', $FName or die "Can't open $FName: $!\n"; my $FName = shift // die "Expected a filename!"; use warnings; use strict; # foo.pl - print a file in reverse

Sometimes a file is too big to handle that way, though that's increasingly rare with modern computers. But if so, you could always use a program (such as tac) that will reverse the file for you, and then you can process the file in order in your code.

For one-off jobs, that's the way I'd go. But if you always need to process the files in reverse, I'd use the File::Backwards module that stevieb suggested.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Replies are listed 'Best First'.
Re^2: Reading the contents of a file from the bottom up
by Scotmonk (Sexton) on Nov 24, 2019 at 21:49 UTC
    thankyou

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