*        Substring/Top and tail    04/03/2017
SUBSTRTT CSECT
         USING  SUBSTRTT,R13       base register
         B      72(R15)            skip savearea
         DC     17F'0'             savearea
         STM    R14,R12,12(R13)    save previous context
         ST     R13,4(R15)         link backward
         ST     R15,8(R13)         link forward
         LR     R13,R15            set addressability
*
         XPRNT  S8,L'S8            print s8
         MVC    S7,S8+1            s7=substr(s8,2,7)
         XPRNT  S7,L'S7            print s7
         MVC    S7,S8              s7=substr(s8,1,7)
         XPRNT  S7,L'S7            print s7
         MVC    S6,S8+1            s6=substr(s8,2,6)
         XPRNT  S6,L'S6            print s6
*
         L      R13,4(0,R13)       epilog
         LM     R14,R12,12(R13)    restore previous context
         XR     R15,R15            rc=0
         BR     R14                exit
S8       DC     CL8'12345678'
S7       DS     CL7
S6       DS     CL6
         YREGS
         END    SUBSTRTT