a simple RegExp question

[S. Levent Yilmaz]

Hello,

It sounded like a very simple problem but I couldn't come up with an
elegant solution. The problem is:

Find all lines which contain a given word (say 'kitty') not preceded
with another given word (say 'puppy') . For instance:

I have two pets:
my kitty is very cute
but puppy is cuter than kitty

What regular expression stands only for the 2nd line? Note that the
other way around is very easy, that is the lines with 'puppy' followed
by 'kitty' is only "puppy.*kitty"
Is this possible at all with a single RegExp?

thank you so very much!
-Levent.

 

[Gunnar Hjalmarsson]

Find all lines which contain a given word (say 'kitty') not
preceded with another given word (say 'puppy') . For instance:

I have two pets:
my kitty is very cute
but puppy is cuter than kitty

What regular expression stands only for the 2nd line? Note that the
other way around is very easy, that is the lines with 'puppy'
followed by 'kitty' is only "puppy.*kitty"
Is this possible at all with a single RegExp?

Don't know, but why not just do:

/\bkitty\b/ and !/\bpuppy\b.*\bkitty\b/

 

[Richard Morse]

Hello,

It sounded like a very simple problem but I couldn't come up with an
elegant solution. The problem is:

Find all lines which contain a given word (say 'kitty') not preceded
with another given word (say 'puppy') . For instance:

I have two pets:
my kitty is very cute
but puppy is cuter than kitty

What regular expression stands only for the 2nd line? Note that the
other way around is very easy, that is the lines with 'puppy' followed
by 'kitty' is only "puppy.*kitty"
Is this possible at all with a single RegExp?

thank you so very much!
-Levent.

You're looking for negative look-behind assertion. (I think).

perldoc perlre

look for "look-behind".

Short form:

my $line =~ m/(?<!puppy).*kitty/;

HTH,
Ricky

 

[Gunnar Hjalmarsson]

You're looking for negative look-behind assertion. (I think).

Think? How about testing the code before posting?

Short form:

my $line =~ m/(?<!puppy).*kitty/;

That matches any line containing "kitty".

 

[Matt Garrish]

Don't know, but why not just do:

/\bkitty\b/ and !/\bpuppy\b.*\bkitty\b/

Or if the OP had bothered to read a bit of perlre:

/\bkitty\b/ and $` !~ /\bpuppy\b/

Matt

 

[Gunnar Hjalmarsson]

You have failed to indicate if "kitty" followed by "puppy" is
permissible or to be ignored.

How do you define "preceded"?