regex look behind and in front

[gruntydatsun]

Any help with this regular expression greatly appreciated.

I have a string to search and want to wrap instances of the word derp like this  <b>derp</b>

unless it appears in these words @derp,derpina,derpatitis,derpmessage

it sort of works but it falls over when you have the word 'headerpmessage' or @derp as exclusions.  If something appears before the derp it fails.

I'm a bit lost in how to do look behind and look infront here.  Any help greatly appreciated.

$string = "the derp we need and dave@derp.com and derpatitis "      ;string i'm searching for derp
$string &= "and headerpmessage we dont want when searching derp out"    ;but not some variations of derp
$term = "derp"                              ;term i'm looking for
$exclusion = "@derp,derpina,derpatitis,derpmessage"         ;variations i don't want detected
$exclude = StringReplace($exclusion,",","|")                ;create exclusion list delimited by |
$pattern = '(?!' & $exclude & ')' & $term               ;build exclusions regex
$repl_with = '<b>' & $term & '</b>';                    ;string to insert when match found
$answer = StringRegExpReplace($string,$pattern,$repl_with)      ;find pattern in string and replace with
msgbox(1,"ANSWER",$answer)                      ;results                        ;the answer

[Realm]

How about this?

$string = "the derp we need and dave@derp.com and derpatitis "      ;string i'm searching for derp
$string &= "and headerpmessage we dont want when searching derp out"    ;but not some variations of derp
$term = "derp"                              ;term i'm looking for
$pattern = ' ' & $term & ' '               ;build exclusions regex
$repl_with = '<b>' & $term & '</b>';                    ;string to insert when match found
$answer = StringRegExpReplace($string,$pattern,$repl_with)      ;find pattern in string and replace with
msgbox(1,"ANSWER",$answer)                      ;results                        ;the answer

Edit: This will not include when followed by punctuation. Such as "derp."

This can be fixed by converting $pattern to an array and utilizing the different terms and replacements in a loop.

Basic Example:

$string = "the derp we need and dave@derp.com and derpatitis " 
$string &= "and headerpmessage we dont want when searching derp out"  
$term = "derp"                      

Local $aPattern[3][2]
$aPattern[0][0] = ' ' & $term & ' ' 
$aPattern[0][1] = ' <b>' & $term & '</b> '
$aPattern[1][0] = ' ' & $term & '\.'
$aPattern[1][1] = ' <b>' & $term & '</b>.'
$aPattern[2][0] = ' ' & $term & '\!'
$aPattern[2][1] = ' <b>' & $term & '</b>!'

Local $answer = $string
For $i = 0 To UBound($aPattern)-1
    $answer = StringRegExpReplace($answer,$aPattern[$i][0], $aPattern[$i][1])
Next

msgbox(1,"ANSWER",$answer)

Hope this helps a bit.

Happy Coding!

Realm

Edited September 5, 2013 by Realm

[jchd]

Let's try this:

Local $string = "the derp we need and dave@derp.com and derpatitis " & _
                "and headerpmessage we dont want when searching derp out"

Local $answer = StringRegExpReplace($string, "\b(?<!@)(derp)\b", "<b>\1</b>")

MsgBox(1, "ANSWER", $answer)

[kylomas]

@jchd - Is a word boundry any char that is not a-z and A-Z?  I'm trying to understand why the "@" is a word boundry necessitating the look behind assertion.

Incidentally, nice job on the beta Helpfile for SRE related topics.  Do you use Expresso at all?

kylomas

[mikell]

@kylomas

'@' is a W character so b matches its position and the lookbehind is needed to ignore this match

[kylomas]

@mikell - Thanks

[jchd]

Nespresso? What else?

No I only drink genuine ristretto coffe from on-demand ground beans. Tasteful and low on caffeine.

[kylomas]

@mikell - Got it now, any char that is not a digit, letter or underscore (thanks to the beta doc by jchd)

[jchd]

Thanks for reading!