CODEWITHSUNDEEP
perl
SIMEL
SIMEL

Reputation: 8939

Reading a line from a file without advancing the line counter with Perl

I want to be able to read the "next line" without increasing the line counter, so that the next time a read command is isued it will read the same line.

example:

this is the first line
this is the second line
this is the third line

I want to be able to know that the second line says "this is the second line" but not advancing my counter so that my program:

print <>;
print unknown_read_command;
print <>;

will print on the screen:

this is the first line
this is the second line
this is the second line

And in a more general, how can I change and move the pointer to the line in any direction and any amount that I want?

Upvotes: 4

Views: 1444

Answers (2)

Alex Reynolds
Alex Reynolds

Reputation: 96974

If you're reading line by line, another way to do this is with Tie::File:

#!/usr/bin/perl 

use strict;
use warnings;
use Tie::File;

my $fn = "foo.bar";

tie my @myFileLines, 'Tie::File', $fn or die "$?";

print STDOUT $myFileLines[0];
print STDOUT $myFileLines[1];
print STDOUT $myFileLines[1]; # print second line twice

untie @myFileLines;

Using file seek methods is more generic and you'll have to search for newline delimiters yourself, which Windows complicates with a proprietary newline.

Upvotes: 3

Eugene Yarmash
Eugene Yarmash

Reputation: 150111

You can fetch the file position for a filehandle with tell, and set it with seek:

my $pos = tell $fh;
# ...
seek $fh, $pos, 0 or die "Couldn't seek to $pos: $!\n";

Upvotes: 7

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