topic Re: Simple perl question in Operating System - HP-UX

Simple perl question

Jeff Picton — Tue, 22 Jun 2004 08:25:56 GMT

Hello

When using the "next if" loop in perl, what is the correct syntax for :-

next if ($x ne "some string")

Jeff

Re: Simple perl question

harry d brown jr — Tue, 22 Jun 2004 08:29:51 GMT

man perlsyn

next some boolean operation;
or
next;

live free or die
harry

Re: Simple perl question

H.Merijn Brand (procura — Tue, 22 Jun 2004 08:30:12 GMT

that is OK, though I myself prefer

$x eq "some string" or next;

Enjoy, Have FUN! H.Merijn

Re: Simple perl question

Rodney Hills — Tue, 22 Jun 2004 08:37:53 GMT

"if" in this case is using the modifier syntax which is availabe on all expressions. Example-

print "hello" if $x > 5;

"unless" is also a modifier-

print "hello" unless $x <= 5;

In your example, the parenthesis aren't required, and using the "unless" modifier you get-

next unless $x eq "some string";

HTH

-- Rod Hills

Re: Simple perl question

Jeff Picton — Tue, 22 Jun 2004 08:45:58 GMT

Hi

Thanks for the replies. This is the full problem (I wish to print all the values of $last_field except the ones containing the string).

$last_field=pop(@array);
next unless ($last_field eq "some_string");

Jeff

Re: Simple perl question

harry d brown jr — Tue, 22 Jun 2004 08:50:49 GMT

printf("%s",$last_field) unless ($last_field eq "some_string");

live free or die
harry

Re: Simple perl question

Jeff Picton — Tue, 22 Jun 2004 08:55:23 GMT

I meant to mention that I was printing to file not screen

Re: Simple perl question

harry d brown jr — Tue, 22 Jun 2004 08:58:39 GMT

open(OUTPUTFILEPTR,"> /tmp/somefilename");

some loop:

printf(OUTPUTFILEPTR "%s",$last_field) unless ($last_field eq "some_string");

live free or die
harry

Re: Simple perl question

Jeff Picton — Tue, 22 Jun 2004 09:02:33 GMT

This should work, however it does not strip out the unwanted list of strings.

I think it may be the fact I used the pop function on an array.

Re: Simple perl question

harry d brown jr — Tue, 22 Jun 2004 09:29:17 GMT

something like this?

#!/usr/bin/perl
#
@arrSTUFF="";
while () {
push @arrSTUFF,$_;
}
foreach $last_field (@arrSTUFF) {
printf("%s\n",$last_field) unless ($last_field =~ "crazyman");
}

You can use "chomp" to remove "CR's" after the foreach line above:
chomp($last_field);

live free or die
harry

Re: Simple perl question

H.Merijn Brand (procura — Tue, 22 Jun 2004 09:56:30 GMT

Almost right. Running that with (the recommended) -w switch would yield a warning, because an array is not initialized with a string, but with a list.

Knowing that, the initialization isn't needed at all, and the chomp can be done in one go

=~ operator doesn't take " as delimiter without the m prefix

For automatically aliasses $_, and printf isn't needed for a single string. The added \n (newline can be shorthanded to the -l command line opting, reducing Harry's snippet to the syntacticcally valid:

#!/usr/bin/perl -wl
chomp (my @arr = );
for (@arr) {
print unless /crazyman/;
}

Enjoy, Have FUN! H.Merijn

Re: Simple perl question

Gregory Fruth — Tue, 22 Jun 2004 12:02:28 GMT

Perl's "grep" function might do what you
want in one step:

@array2 = grep(/^some_string$/, @array);

The array @array2 will be the subset of
items from @array that are not "some_string".
The ^ and $ anchor the pattern so that you
match "some_string" exactly and do not match
"also_some_string" or "some_string_or_other".

Re: Simple perl question

R. Allan Hicks — Wed, 23 Jun 2004 14:47:08 GMT

Following example from PERL Black Book by Steven Holzner page 213 published by Coriolis

To trap for division by zero:

@a(0 .. 20)
@b(-10 .. 10)

DIVISION: while(@a){
$a=pop @a;
$b=pop @b;

next DIVISION if ($b == 0);
print "$a / $b = ".$a/$b."\n";
}

when $b==0, it skips to the end of the loop.