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.STRING_FUNCS: SUBSTR (Substring) Function
.ALIAS.......: SUBSUBFU
.DISCUSSION..:
This function returns a substring of the string supplied in the /Q parm, starting in the column supplied in the /A parm, for a length supplied in the /B parm.

The start column specified in the /A parm may be a negative number; if it is, then the start column is calculated from the end of the string rather than from the beginning. This feature makes it easy to extract the rightmost characters of a string.

Specifically, when the ParmA is negative, the start position is calculated using the following formula:


 EXAMPLE....:  Fdate /Fsubstr  /A-2 /Qabcd

CALCULATION: StartColumn = length(ParmQ) + 1 + ParmA
StartColumn = 4 + 1 + (-2) = 3



.EXAMPLES:
          Fdate /Fsubstr /A7 /B2 /Q"STEVE FERG"   ===> "FE"
           Fdate /Fsubstr /A7     /Q"STEVE FERG"   ===> "FERG"
           Fdate /Fsubstr     /B5 /Q"STEVE FERG"   ===> "STEVE"

     EXAMPLES using a negative start position:
          Fdate /Fsubstr /a-6 /B3 /Q"1994 Jun 03"   ===> "Jun

          rem extract the rightmost 6 characters of a string
           Fdate /Fsubstr /a-6     /Q"1994 Jun 03"   ===> "Jun 03"

  rem pad YEAR environment variable to the left with zeroes,
  rem to make sure it is 4 bytes long
  Fdate /Fsubstr /A-4 /q0000%year% /vyear


     REMEMBER that Fdate eliminates redundant spaces when obtaining its
     parameter input:

           Fdate /Fsubstr /A7     /Q"STEVE FERG"      ===> "FERG"
           Fdate /Fsubstr /A7     /Q"STEVE  FERG"     ===> "FERG"
           Fdate /Fsubstr /A7     /Q"STEVE    FERG"   ===> "FERG"