Would somebody please explain?

[Henry McGilton]

In article <1991Apr21.023416.5795 at mp.cs.niu.edu>, rickert at mp.cs.niu.edu (Neil Rickert) writes:
    *  In article <1991Apr21.001702.5661 at umbc3.umbc.edu> rouben at math16.math.umbc.edu (Rouben Rostamian) writes:

        **  The command:
        **        expr "Match" : "Ma"
	**  returns 2, as it should, since the first two characters
	**  of "Match" and "Ma" coincide.  Now, would somebody please
        **  explain why the command:
	**        expr "match" : "ma"
        **  complains of a "syntax error"?

    *  I just ran:  strings /bin/expr
    *  From the output I would guess that 'match', 'index', 'substr' and
    *  'length' are builin functions or operators for 'expr', although
    *  they are not documented in any man pages that I have seen.
    *  I don't know the syntax for using them either.
    *  I guess this is one of those questions to cross post to wizards.
I hope not.  From SunOS  expr  manual page (last updated 5 January 1988):

    ``Note: the match, substr, length, and index operators cannot
      themselves be used as ordinary strings.''

	........  Henry