/*REXX*/
MYSTR = 'MY TEST STRING'
SAY MYSTR
MYSTR = STRREPLACE(MYSTR,"TEST","NEW")
SAY MYSTR
EXIT                                                               

/* A FUNCTION TO DO A STRING REPLACE */
STRREPLACE:
   ORIGINAL = ARG(1)
   OLDTXT   = ARG(2)
   NEWTXT   = ARG(3)
   NEWSTR = ORIGINAL
   DO WHILE POS(OLDTXT,NEWSTR) > 0
      NEWSTR = SUBSTR(NEWSTR, 1 , POS(OLDTXT,NEWSTR)-1) ||,
               NEWTXT || SUBSTR(NEWSTR, POS(OLDTXT,NEWSTR) + LENGTH(OLDTXT))
   END
   RETURN NEWSTR