The substring function extracts a substring from a string or symbol. If applied to a string, a string is returned. If applied to a symbol, a symbol is returned.

If a range is specified for range, and m and n evaluate to integers then substring will extract a substring from string starting with the mth character and ending with the nth character.

Specifying a single integer m for range is equivalent to specifying the range m..m.

Negative values for m and/or n stand for positions counted leftwards from the right end of the string.  The range 1..-1 refers to the entire string. The range -20..-1 refers to the last 20 characters of the string.

If n is greater than the length of string then substring returns a string from the mth character to the end of string. If m is equal to n + 1 then substring returns the null string.

Zero values for m and/or n are not permitted, except for the case m = 1 and n = 0, which returns the null string as described above.

If either m or n fails to evaluate to an integer, then substring remains unevaluated.

The substring command is thread-safe as of Maple 15.

For more information on thread safety, see index/threadsafe.