string manipulation question

iakobski has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to neaten up a code smippet in the following style:

my $str = "a load of constant stuff...";
$str .= "optional bit in the middle " if $option;
$str .= "loads more stuff";
[download]

now this goes on in the same vein for a while, with a whole heap of variable interpolation and $str is in fact a messy looking array dereference.

In the process of making this more readable, I have written

my $str = "a load of constant stuff...";
        . ($option ? "optional bit in the middle " : undef);
        . "loads more stuff";
[download]

I don't like the look of that 'undef' in the middle of there, but if I change the bit in parentheses for ( "optional bit in the middle" if $option ) I get a syntax error.

What idiom is there to make this clearer and more readable?

-- iakobski

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Re: string manipulation question by how do i know if the string is regular expression (Initiate) on May 18, 2001 at 17:13 UTC
Actually, you're second code block is bad... but I'm guessing that was just a mistake on entering it here. You have too many '`;`'s. But onto the real question... I don't see any better looking way other then replacing the `undef` with `''`. Like so: `my $str = "a load of constant stuff..." . ($option ? "optional bit in the middle " : '') . "loads more stuff";` [download] In fact, if you're using `#!/usr/bin/perl -w` and use the `undef` method, you'll get the following warning: `Use of uninitialized value in concatenation (.) or string at ./pm.pl l +ine 7.` [download] If `$option` returns false. - FrankG	[reply] [d/l] [select]
Re: string manipulation question by dempa (Friar) on May 18, 2001 at 17:22 UTC
I dunno if this more readable or not, but anyway: `my $str = "a load of constant stuff..." . ($option && "optional bit in the middle ") . "loads more stuff";` [download] update: Ofcourse davorg is correct. Why do I never learn to test my code before posting! :) `$option = 0; # Prints out the 0, not good. $option = ""; # This works. $option = undef; # Warnings with -w` [download] /dempa	[reply] [d/l] [select]
Re: Re: string manipulation question by davorg (Chancellor) on May 18, 2001 at 17:36 UTC
Depends what you set `$option` when you don't want the text included. Try it with `0` and see what happens. -- <http://www.dave.org.uk> "Perl makes the fun jobs fun and the boring jobs bearable" - me	[reply]
Re: Re: string manipulation question by Anonymous Monk on May 18, 2001 at 19:06 UTC
of course you could write `my $str = "a load of constant stuff..." . (defined($option) && "optional bit in the middle ") . "loads more stuff";` [download]	[reply] [d/l]
Re: Re: Re: string manipulation question by Anonymous Monk on May 18, 2001 at 19:10 UTC
!! does wonders too. `my $str = "a load of constant stuff..." . (!!$option && "optional bit in the middle ") . "loads more stuff";` [download]	[reply] [d/l]
Re: Re: Re: Re: string manipulation question by dempa (Friar) on May 19, 2001 at 01:36 UTC
Re: string manipulation question by grinder (Bishop) on May 18, 2001 at 18:09 UTC
Interpolate the optional bit via a code reference `@{[ ... ]}` . `my $str = <<FOO; a load of constant stuff... @{["optional bit in the middle " if defined $option]} loads more stuff FOO` [download] Beware that as this example stands, you'll get a newline regardless of whether `$option` is defined or not, but I'm sure you can figure out how to make it do The Right Thing. -- `g r i n d e r`	[reply] [d/l]
Re: Re: string manipulation question by Anonymous Monk on May 18, 2001 at 18:58 UTC
for instance do the newlinine in the ref `my $str = <<FOO; a load of constant stuff...@{[ "optional bit in the middle " if defined $option ]}loads more stuff FOO` [download]	[reply] [d/l]