code:

---

$old_string="[old string]" ; - your old string value -
$new_string="<new string>" ; - your new string value -
;
$file="c:\your_file.txt"   ; - your file -
$file_temp="%temp%\dummy.tmp"
$debug_mode="yes"
IF (Exist($file) = 1)
  DEL $file_temp
  IF (Open(1,$file,2) = 0) ; -read access-
    IF (Open(2,$file_temp,5) = 0) ; -write access-
      $line=ReadLine(1)
      WHILE (@error = 0)
        IF ($debug_mode = "yes")
          ? "  -> "+$line
        ENDIF
        $i=Instr($line,$old_string)
        IF ($i <> 0)
          IF ($i = 1)
            $nline=$new_string+Substr($line,Len($old_string)+1)
          ELSE
            IF ($i+Len($old_string)-1 = Len($line))
              $nline=Substr($line,1,Instr($line,$old_string)-1)+$new_string
            ELSE
              $nline=Substr($line,1,Instr($line,$old_string)-1)+
                     $new_string+
                     Substr($line,Instr($line,$old_string)+Len($old_string))
            ENDIF
          ENDIF
        ELSE
          $nline=$line
        ENDIF
        IF ($debug_mode = "yes")
          ? " --> "+$nline
        ENDIF
        IF (WriteLine(2,$nline+CHR(13)+CHR(10)) <> 0)
        ENDIF
        $line=ReadLine(1)
      LOOP
      IF Close(2)
      ENDIF
    ENDIF
    IF Close(1)
    ENDIF
    ?
    IF (Exist($file_temp) = 1)
      COPY $file_temp $file /H
      IF (@error <> 0)
        ? "Warning KIX: update "+Ucase($file)+" returns error @error (@serror)"
      ELSE
         DEL $file_temp
      ENDIF
      ? "update "+Ucase($file)+" file."
    ENDIF
  ENDIF
  ? "update completed."
ELSE
  ? "already updated."
ENDIF

---

code:

---

[old string]123456789
123[old string]456789
123456789[old string]

---

code:

---

<new string>123456789
123<new string>456789
123456789<new string>

---

code:

---

  -> [old string]123456789
 --> <new string>123456789
  -> 123[old string]456789
 --> 123<new string>456789
  -> 123456789[old string]
 --> 123456789<new string>

update c:\your_file.tx file.
update completed.

---