Perl, Ternary Conditional Operator Question

Jonathan Cunningh
#1 / 8

Ternary Conditional Operator Question

Ok folks.

I'm usually pretty good at figuring this stuff out, but this one is

I'm trying to see if $slash =~ m{/} is a match, and then I want to do
a substitution on $_ depending on the outcome of the match. I've
tried a million ways to parenthesize, but no luck.

Could someone out there please let me know why this doesn't work:

# $slash == '';

$slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

# This doesn't work either...
# ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
}

I'm hoping this is going to be a "duh" moment for me.

Thanks,

Jonathan

Sun, 04 Jan 2004 04:55:28 GMT

John W. Krah
#2 / 8

Ternary Conditional Operator Question

Quote:

> Ok folks.

> I'm usually pretty good at figuring this stuff out, but this one is

> I'm trying to see if $slash =~ m{/} is a match, and then I want to do
> a substitution on $_ depending on the outcome of the match. I've
> tried a million ways to parenthesize, but no luck.

> Could someone out there please let me know why this doesn't work:

> # $slash == '';

You've set the value of $slash to the null string so it will never match
m{/}.

Quote:

> $slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

This doesn't make much sense. If the string has a slash in it then
change all back-slashes to slashes. However, if the string has _no_
slashes in it then change the slashes (which aren't there) to
back-slashes.

Quote:

> # This doesn't work either...
> # ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
> }

> I'm hoping this is going to be a "duh" moment for me.

You think?

John
--
use Perl;
program
fulfillment

Sun, 04 Jan 2004 06:49:09 GMT

Ren Maddo
#3 / 8

Ternary Conditional Operator Question

Quote:

> Ok folks.

> I'm usually pretty good at figuring this stuff out, but this one is

> I'm trying to see if $slash =~ m{/} is a match, and then I want to
> do a substitution on $_ depending on the outcome of the match. I've
> tried a million ways to parenthesize, but no luck.

> Could someone out there please let me know why this doesn't work:

> # $slash == '';

> $slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

> # This doesn't work either...
> # ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
> }

> I'm hoping this is going to be a "duh" moment for me.

Seems to work fine for me -- perhaps the problem is actually somewhere
else? You didn't actually say in what way this failed. Can you give
a complete script that demonstrates the problem?

--
Ren Maddox

Sun, 04 Jan 2004 05:19:59 GMT

$Bill Luebker
#4 / 8

Ternary Conditional Operator Question

Quote:

> Ok folks.

> I'm usually pretty good at figuring this stuff out, but this one is

> I'm trying to see if $slash =~ m{/} is a match, and then I want to do
> a substitution on $_ depending on the outcome of the match. I've
> tried a million ways to parenthesize, but no luck.

> Could someone out there please let me know why this doesn't work:

> # $slash == '';

> $slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

> # This doesn't work either...
> # ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
> }

> I'm hoping this is going to be a "duh" moment for me.

# either of these will do - there is no need for a ternary op

s{/}{\\}g;
# s{/}{\\}g if m{/};

Quote:

}

--
,-/- __ _ _ $Bill Luebkert ICQ=14439852

/ ) /--< o // // http://dbecoll.webjump.com/ (Free site for Perl)
-/-' /___/_<_</_</_ Castle of Medieval Myth & Magic http://www.todbe.com/

Sun, 04 Jan 2004 09:07:44 GMT

Wyzell
#5 / 8

Ternary Conditional Operator Question

Quote:

> Ok folks.

> I'm usually pretty good at figuring this stuff out, but this one is

> I'm trying to see if $slash =~ m{/} is a match, and then I want to do
> a substitution on $_ depending on the outcome of the match. I've
> tried a million ways to parenthesize, but no luck.

> Could someone out there please let me know why this doesn't work:

> # $slash == '';

> $slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

> # This doesn't work either...
> # ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
> }

I'll jump in and ask 'are you trying to solve the wrong problem?'

What are you trying to achieve?

You do realise that forward slashes are quite acceptable in a Perl program
on a Win32 box?

Wyzelli
--
($a,$b,$w,$t)=(' bottle',' of beer',' on the wall','Take one down, pass it
around');
for(reverse(1..100)){$s=($_!=1)?'s':'';$c.="$_$a$s$b$w\n$_$a$s$b\n$t\n";
$_--;$s=($_!=1)?'s':'';$c.="$_$a$s$b$w\n\n";}print"$c*hic*";

Sun, 04 Jan 2004 09:29:39 GMT

Jonathan Cunningh
#6 / 8

Ternary Conditional Operator Question

Quote:

> > Could someone out there please let me know why this doesn't work:

> > # $slash == '';

> > $slash =~ m{/} ? s{\\}{/}g : s{/}{\\}g;

> > # This doesn't work either...
> > # ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;
> > }

> I'll jump in and ask 'are you trying to solve the wrong problem?'

> What are you trying to achieve?

> You do realise that forward slashes are quite acceptable in a Perl program
> on a Win32 box?

> Wyzelli

Sorry for being so vague, but I expected it not to work for you the
same way it didn't work for me. :) First of all, I'm trying to
change all backslashes to forwards and likewise because I'm writing
some code for a poorly planned system that sometimes requires forward
slashes and sometimes not (lame).

When I run the above code I get an "unable to modify [something
something]" with -w (without -w the code just stopped running with no
complaints).

(which happed to be the params passed to my sub. I fixed it by

it wouldn't work tho'.

Is that better?

Thanks,

JC

Here's the whole thing:

package TeamSite::Utils;

use strict;

sub new {
my $self = {};
bless $self;
return $self;

Quote:

}

sub slashFix {
# Takes an array of strings or an array of variables as it's
# first argument(s) and an optional slash (/) as its last.
# If the last argument is not a slash, all of the previoius
# arguments will have their slashes changed to backslashes(\).
# If the last argument is a slash, all previous arguments will
# have their backslashes changed to slashes. Returns an array
# of processed arguments if called in list context, and
# returns a string if called in string context.
my $self = shift;

($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;

$_);
}

Quote:

}

1; # True-Value Hardcode

Mon, 05 Jan 2004 06:40:05 GMT

$Bill Luebker
#7 / 8

Ternary Conditional Operator Question

Quote:

> You do realise that forward slashes are quite acceptable in a Perl program
> on a Win32 box?

Not everywhere - shelling out can be a problem.

--
,-/- __ _ _ $Bill Luebkert ICQ=14439852

/ ) /--< o // // http://dbecoll.webjump.com/ (Free site for Perl)
-/-' /___/_<_</_</_ Castle of Medieval Myth & Magic http://www.todbe.com/

Mon, 05 Jan 2004 07:14:31 GMT

Tad McClell
#8 / 8

Ternary Conditional Operator Question

Quote:

>> > Could someone out there please let me know why this doesn't work:

[ snip code that *does* work ]

Quote:

>> What are you trying to achieve?
>Sorry for being so vague, but I expected it not to work for you the

^^^^^^^^^^

Just write it in the form of a short and complete program, then
run the program, _then_ post that code.

Then we will be troubleshooting the same code that you have,
instead of wasting time on code that does not even really exist.

Quote:

>When I run the above code I get an "unable to modify [something
>something]" with -w (without -w the code just stopped running with no
>complaints).

You should include the exact message text if you want help diagnosing
the problem.

Quote:

>(which happed to be the params passed to my sub. I fixed it by

>it wouldn't work tho'.

Because function args are aliases.

Quote:

>Is that better?

No. It does not execute either.

We cannot see the method call. I'll bet the args in the call
are not lvalues, but I can't really tell because I am troubleshooting
invisible code...

Quote:

>Here's the whole thing:

>package TeamSite::Utils;
>sub slashFix {
> my $self = shift;

^^^^^^

Perl has operators for testing equality. You should use one of
them when you want to test for equality:

^^^^^^^^^^^

The reason would be revealed if we could see the method call.

But we can't. So we cannot help with your real problem...

Quote:

> ($slash =~ m{/}) ? s{\\}{/}g : s{/}{\\}g;

^^^^^^^^^ ^^^^^^^^^

the caller. That would be OK with:

but would complain with:

$util->slashFix( qw/zero one two three/ );

because the are not lvalues in the second case.

--
Tad McClellan SGML consulting

Fort Worth, Texas

Mon, 05 Jan 2004 07:31:10 GMT