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Substitution not working in RegExp

LeoF
Novice

Aug 12, 2000, 6:32 PM

Post #1 of 3 (1542 views)

Substitution not working in RegExp	Can't Post

Hello everyone,

I'm trying to remove leading and trailing spaces and blank lines from a string but is not working, is only doing it for the first match. Could someone be so kind as to give me any insight on this code?

<BLOCKQUOTE>code:<HR>

$var = "leave intact]

123";

$var2 = "123

[leave intact";

$var =~ s/(\] |\]\n)+/\]/g;
$var2 =~ s/( \[|\n\[)+/\[/g;

print "\$var = $var \n\n";
print "\$var2 = $var2 \n\n";
</pre><HR></BLOCKQUOTE>

I would like to remove every space and blank line after "]" and before "[" so that I get "leave intact]123" and "123[leave intact" as a result.

Any comments and suggestions would be greatly appreciated.

Thanks in advance for your cooperation.

Be Well

[This message has been edited by LeoF (edited 08-12-2000).]

japhy
Enthusiast / Moderator

Aug 12, 2000, 9:27 PM

Post #2 of 3 (1542 views)

Re: Substitution not working in RegExp [In reply to]	Can't Post

Your problem is that the substitution starts where it left off.

<BLOCKQUOTE>code:<HR>

$str = "abXXXc";
$str =~ s/bX/b/g;
# $str is now "abXXc"
</pre><HR></BLOCKQUOTE>

This code doesn't remove all the X's after the b, only the first one:

<BLOCKQUOTE>code:<HR>

# the [] means "the regex starts looking here"

string: [a]bXXXc
regex: s/bX/b/
match: abXXXc # changes 'bX' to 'b'

string: ab[X]Xc
regex: s/bX/b/
no match
</pre><HR></BLOCKQUOTE>

You would want something like:

<BLOCKQUOTE>code:<HR>

1 while $str =~ s/bX/b/;
</pre><HR></BLOCKQUOTE>

But this can be optimized, since we can just say:

<BLOCKQUOTE>code:<HR>

$str =~ s/bX+/b/; # change a 'b' followed by 1 or more X's to 'b'
</pre><HR></BLOCKQUOTE>

We could tack on a /g modifier if there'd be more than one set of bXXX... in the string.

We can be even neater, and use a positive look-behind assertion:

<BLOCKQUOTE>code:<HR>

$str =~ s/(?<=b)X+//;
# change 1 or more X's to "" IF the first X is preceeded by a b
</pre><HR></BLOCKQUOTE>

Modify/alter to fit your code accordingly.

------------------
Jeff "japhy" Pinyan -- accomplished author, consultant, hacker, and teacher

[This message has been edited by japhy (edited 08-12-2000).]

LeoF
Novice

Aug 13, 2000, 8:19 PM

Post #3 of 3 (1542 views)

Re: Substitution not working in RegExp [In reply to]	Can't Post

Thanks a lot Jeff, I appreciate it, as always your post is very didactical, your explanation helped me to fix another regexp too.

I changed the code above to:

$var =~ s/\]\s+/\]/g;

and

$var2 =~ s/\s+\[/\[/g;

and it works as intended, I used \s to account for all white space, now I know where the + goes, thanks.

I have another regexp that is not working and I hope you can give me a hand with it:

<BLOCKQUOTE>code:<HR>

$message = <<HTML;
 Testing mixed attributes @ 123

Leave this text intact

<DIV STYLE="font-size:80"> Testing mixed attributes @ 123 </DIV>
HTML

$message =~ s/( )(.+?)(<\/SPAN> )/\[size=$2\]$4\[\/size\]/isg;

$message =~ s/(<DIV STYLE="font-size : )(\d+)("> )(.+?)(<\/DIV> )/\[size=$2\]$4\[\/size\]/isg;

$message =~ s/( )(.+?)(<\/SPAN> )/\[color=$2\]$4\[\/color\]/isg;

$message =~ s/( )(.+?)(<\/b> )/\[b\]$2\[\/b\]/isg;

print "message = \n $message \n\n\n";
</pre><HR></BLOCKQUOTE>

As a result I get:

<BLOCKQUOTE>code:<HR>

message =
[size=80] [color=red]Testing mixed attributes @ 123[/color]

Leave this text intact

[size=80] [color=red]Testing mixed attributes @ 123 [/color]
</pre><HR></BLOCKQUOTE>

I was able to get this code to work after reading your post.

As you can see, in the fist case it mismatches the tags when I use SPAN for both size and color. If I change the tags for size to DIV and keep SPAN for color it works, but I wonder if I can make it account for nesting SPAN or other tags?

Any comments and suggestions would be greatly appreciated.

Thank you for your time and attention.

Be Well

(had to put some extra spaces to avoid smilies and bolding)

[This message has been edited by LeoF (edited 08-13-2000).]

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