On 21/08/2011 12:33, Ron Weidner wrote:
>
> Recently, I was asked to find the first occurrence of a word in a
> text file and replace it with an alternate word. This was my
> solution. As a new Perl programmer, I feel like this solution was too
> C like and not enough Perl like. So, my question is what would have
> been the Perl like solution to this problem?
>
> In this example there is little risk of running out of memory
> reading the file. But had this been a production environment or an
> unknown file size, I would have had to consider that.
>
>
> #!/usr/bin/perl
> use strict;
> use warnings;
>
> #program finds the first occurrence of the word Dood and
> #replaces it with the word Dude in the file data.txt.
>
> open FP, "+<", "data.txt" || die "Cant open data.txt " . $!;
>
> my @buffer =<FP>;
> seek FP,0,0;
> my $do_replace = 1; #used to control replacing in multiline files.
> my $line;
> my $data;
> foreach $data (@buffer)
> {
> if ($do_replace == 1)
> {
> $line = $data;
> $data =~ s/Dood/Dude/;
> if ($line ne $data)
> {
> $do_replace = 0; #we did a substitution so do no more.
> }
> }
> print FP $data;
> }
> close FP;
>
> #Test data
> #Dude! Where's my car?
> #Dood! Where's my car?
> #Dood! Where's my car?
Hey Ronald
Here is a program like yours, that reads the entire file into memory and
then outputs the altered version.
#!/usr/bin/perl
use strict;
use warnings;
#program finds the first occurrence of the word Dood and
#replaces it with the word Dude in the file data.txt.
open my $fp, "<", "data.txt" or die "Cant open data.txt for input: $!";
my @buffer = <$fp>;
open my $fp, ">", "data.txt" or die "Cant open data.txt for output: $!";
my $replaced;
foreach my $line (@buffer) {
unless ($replaced) {
$replaced++ if $line =~ s/Dood/Dude/;
}
}
__END__
But if you may be working with large files and have to be careful with
memory, it is best to process the input file one line at a time. There
are special built-in ways of doing this sort of thing, but it is best
for now to write something that is clear and straightforward. Something
like this perhaps.
#!/usr/bin/perl
use strict;
use warnings;
#program finds the first occurrence of the word Dood and
#replaces it with the word Dude in the file data.txt.
rename 'data.txt', 'data.old' or die "Rename of input file failed: $!";
open my $in, '<', 'data.old' or die "Failed to open input file: $!";
open my $out, '>', 'data.txt' or die "Failed to open output file: $!";
my $replaced;
while (my $line = <$in>) {
unless ($replaced) {
$replaced++ if $line =~ s/Dood/Dude/;
}
print $out $line;
}
__END__
I hope this helps,
Rob
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
For additional commands, e-mail: beginners-h...@perl.org
http://learn.perl.org/
