Regex Buddy by Sigh_ (http://xi.ma.cx)

Usage: /rbuddy

You first add strings by right clicking on the side listbox of the first window.
After strings are added you select one and type a regular expression into the editbox.
As you type it will highlight the matched parts of the selected string.
You can also click on the lines in the listbox to choose a string to handle.
The second window allows you to view the captured parts of an expression.
It also lets you type in a subtext part to substitute for the matched parts of your selected line

alias rbuddy {
  var %- = echo $rb1 $str(-,35)
  if ($window($rb)) window -c $rb
  if ($window($rb1)) window -c $rb1
  window -Bzedh +Ln $rb1 550 250 300 250 "Courier new" 12
  window -azedl25 +nbt $rb 50 250 500 250 "Courier new" 12
  echo $rb Right click this window to access options, type in the next window for substitutions
  %-
  echo $rb1 Captured: 0
  %-
  %-
  echo $rb1 Substitutions: 0
  %-
  echo $rb1 -
}

alias -l rb return @RegexBuddy
alias -l rb1 return $rb $+ 1

dialog -l rbuddy {
  title "Add strings"
  size -1 -1 260 250
  edit "",1,10 10 240 160, multi return
  check "Evaluate variables/identifiers in input",2,30 175 200 20
  button "Add",3,70 205 50 35
  button "Done",4,140 205 50 35,cancel
}

on *:dialog:rbuddy:sclick:3:{
  filter -ik rbuddy 1 _rb
  $null($input($filtered line $+ $iif($filtered != 1,s) added,iou,Success))
}

alias -l _rb aline -l $rb $($1-,$iif($did(rbuddy,2).state,2,1))

menu @RegexBuddy {
  lbclick:{ 
    rline $rb $line($rb,0) $_regcol($sline($rb,1),$editbox($rb))
    _reglist
  }
  Add strings:dialog -arm rbuddy rbuddy
  Add clipboard contents:{ 
    var %i = 1 
    while (%i <= $cb(0)) {
      if ($cb(%i) != $null) aline -l $rb $ifmatch
      inc %i
    }
  }
  Remove selected:while ($sline($rb,1).ln) dline -l $rb $ifmatch
  Remove all:clear -l $rb
  Hide second window:{ 
    window -h $rb1 
    window -sC $rb -1 -1 720 250
  }
  Show second window:{
    window -a $rb1
    window -a $rb
    window -s $rb 50 250 500 250
  }  
}

on *:input:@RegexBuddy*:halt

on *:keydown:@RegexBuddy*:*:{
  if ($keychar) || ($istok(46 38 40,$keyval,32)) .timer 1 0 rline $rb $line($rb,0) $!_regcol($$sline($rb,1),$editbox($rb)) $(|) _reglist
}

on *:active:@RegexBuddy:{
  if ($rb !isin $lactive) && ($window($rb1).state != hidden) {
    window -a $rb1
    window -a $rb
  }
}

on *:close:@RegexBuddy*:window -c $remtok($rb $rb1,$target,32)

alias _reglist {
  var %i = 1
  while ($line($rb1,0) > 7) dline $rb1 4
  .echo -q $regex($sline($rb,1),$editbox($rb))
  rline $rb1 2 Captured: $regml(0)
  while (%i <= $regml(0)) {
    iline $rb1 $calc($line($rb1,0)-3) %i $+ . $regml(%i) - pos: $regml(%i).pos 
    inc %i
  }
  rline $rb1 $calc($line($rb1,0)-2) Substitutions: $regsub($$sline($rb,1),$editbox($rb),$+(1,$chr(44),08,$editbox($rb1),99,$chr(44),99),%i)
  rline $rb1 $line($rb1,0) %i
}

;; Alias to highlight the part of a string a certain regular expression matches
;; $_regcol(string,/exp/)

alias _regcol {
  .echo -q $regex($2,^(?:m(\C)|(?:(/?)))(?:(?:(\C+)\ $+ $iif(m* iswm $2,1,2) $+ (\C*))|(\C+)))
  return $_regsub($1,/( $+ $regml(2) $+ ) $+ / $+ $regml(3),$+(1,$chr(44),08\1,99,$chr(44),99))
} 

;; Returns the result of a regular expression substitution rather than the number of substitutions made
;; $_regsub(string,/expression/,substring)[.n]
;; Using the .n property returns what $regsub usually returns, the number of substitutions

alias _regsub {
  var %m,%x = $regsub($1,$2,$3,%m)
  return $iif($prop = n,%x,%m)
}