diff --git a/BIN/SED.S.TXT b/BIN/SED.S.TXT
index c314cf99..5ecb8f80 100644
--- a/BIN/SED.S.TXT
+++ b/BIN/SED.S.TXT
@@ -21,6 +21,8 @@ hFile                   .BS 1
 hBuf                    .BS 1
 LineNum                 .BS 2
 char                    .BS 1
+delimiter               .BS 1
+replaceidx              .BS 1
 
 bIgnoreCase             .BS 1
 
@@ -100,6 +102,8 @@ CS.RUN.CheckArgs
                                 sta ArgPattern
                                 >LDYA ZPPtr1
                                 >STYA ZPPatternPtr
+                                jsr CS.RUN.SEDParser
+                                bcs .97
                                 bra CS.RUN.CheckArgs
 
 .11                             lda hFile
@@ -185,6 +189,54 @@ CS.RUN.NextArg                  inc ArgIndex
 
 .9                              rts
 *--------------------------------------
+CS.RUN.SEDParser
+* On entry, the expression is in ZPPatternPtr
+* We are looking for "s/search string/replace string/"
+* The '/' delimiter can be any char
+* On exit. ZPPatternPtr points to delimiter-terminated search string, 
+*          replaceidx contains the offset to the start of replacement str
+
+                                stz LineNum               Reusing this as cntr
+
+                                lda (ZPPatternPtr)
+                                cmp #'s'                  Substitute cmd
+                                bne .8                    If not, error
+
+                                ldy #$01                  Delimiter char
+                                lda (ZPPatternPtr),y
+                                sta delimiter             Stash for later
+
+.2                              iny
+                                lda (ZPPatternPtr),y
+                                beq .4                    End of string
+                                cmp delimiter             Is it delimiter?
+                                bne .2
+
+                                inc LineNum               Keep count
+                                lda LineNum
+                                cmp #$01                  Second delim
+                                bne .2
+
+                                sty replaceidx
+                                bra .2
+
+.4                              lda LineNum               Check # of delims
+                                cmp #$02
+                                bne .8
+
+                                inc ZPPatternPtr          Eat 's/'
+                                bne .5
+                                inc ZPPatternPtr+1
+.5                              inc ZPPatternPtr
+                                bne .7
+                                inc ZPPatternPtr+1
+
+.7                              clc
+                                rts                       No error return
+
+.8                              sec
+                                rts
+*--------------------------------------
 CS.RUN.OPEN                     >PUSHYA
                                 >PUSHBI O.RDONLY+O.TEXT
                                 >PUSHBI S.FI.T.TXT
@@ -209,10 +261,12 @@ CS.RUN.PRINT                    >LDYA ZPBufPtr
                                 bne .3
 
                                 lda (ZPPatternPtr),y    EOL
+                                cmp delimiter
                                 bne .7                  Not end of pattern
 *                                                       No match.
 
 .3                              lda (ZPPatternPtr),y
+                                cmp delimiter
                                 beq .5                  Match
 
                                 jsr CS.RUN.toUpper
@@ -241,10 +295,19 @@ CS.RUN.PRINT                    >LDYA ZPBufPtr
                                 clc
                                 rts
 *--------------------------------------
-CS.RUN.GotMatch                 lda #'*'             TODO ...
+CS.RUN.GotMatch                 phy
+                                ldy replaceidx
+                                dey
+.1                              lda (ZPPatternPtr),y
+                                cmp delimiter
+                                beq .5
                                 phy
                                 >SYSCALL PutChar
                                 ply
+                                iny
+                                bra .1
+
+.5                              ply
                                 tya                  Advance ZPPtr1 by Y
                                 clc
                                 adc ZPPtr1
@@ -302,7 +365,8 @@ CS.END
 OptionList          .AS "HhIi"
 OptionList.Cnt      .EQ *-OptionList
 *--------------------------------------
-MSG.USAGE           .AS "Usage : SED <pattern> <File> or CMD|SED <pattern>\r\n"
+MSG.USAGE           .AS "Usage : SED [-I] s/pattern/replacement/ <File>\r\n"
+                    .AS "   or : CMD|SED [-I] s/pattern/replacement/\r\n"
                     .AS "   -I : Ignore Case"
 MSG.CRLF            .AZ "\r\n"
 *--------------------------------------