David Sudjiman wrote:
> This is my script.
>
> ===
> #!/usr/bin/perl
> # ex9-2b.pl
>
> use strict;
> use warnings;
>
> my ($filename) = @ARGV;
>
> open FILE, $filename or die "Can't open $filename : $!";
>
> $^I = ".out";
> while (<FILE>) {
> s/Fred/Larry/i;
> print;
> }
> ===
>
> I executed using:
> $ perl ex9-2b.pl fred_larry.txt
> AlLarry
> Larrydy
> Larrydy Mercury
> Wilma
> wilma
> Larry
> Larrydo
> freedo
> Antonius AlLarry
> Mr. AlLarry
> Mr. Larrydy
> Mrs. Larrydy Mercury
> Ms. Wilma
> Ms. wilma
> Mr. Larry
> Mrs. Larrydo
> Mr. freedo
> Antonius J. AlLarry
> Larry
> Larry
> Larry
> Mr. Larry and Mrs. Wilma
> Larry and Wilma
> Wilma Larry
> Larrywilma
>
> It does the work s/Fred/Larry/i but why didn't want to print back to the
> file.
>
> I'm using different approach like below:
>
> ===
> #!/usr/bin/perl
> # ex9-e.pl
>
> use strict;
> use warnings;
>
> $^I = ".out";
>
> while (<>) {
> s/Fred/Larry/i;
> print;
> }
> ===
>
> It does the replacement and print back. Why differs?
Because the null filehandle inside the readline operator ( <> ) has special
magic which works together with the @ARGV array and the $^I scalar but does
not work with ordinary filehandles.
See the "I/O Operators" section of perlop.pod for an explanation of the null
filehandle and the -i switch entry in perlrun.pod for an explanation of the
$^I variable.
perldoc perlop
perldoc perlrun
John
--
use Perl;
program
fulfillment
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