NAME
    substr - extract a substring of given string

SYNOPSIS
    substr(str, pos, len)

TYPES
    str		string
    pos		nonnegative integer
    len		nonnegative integer

    return	string

DESCRIPTION
    If pos > length of str or len is zero, the null string "" is returned.

    If 1 <= pos <= strlen(str), substr(str, pos, len) returns the
    string of length min(strlen(str) - pos + 1, len) formed by
    consecutive characters of str starting at position pos, i.e. the
    string has length len if this is possible, otherwise it ends with
    the last character of str.  (The first character has pos = 1, the
    second pos = 2, etc.)

    If pos = 0, the result is the same as for pos = 1.

EXAMPLE
    > A = "abcde";
    > print substr(A,0,2), substr(A,1,2), substr(A,4,1), substr(A,3,5)
    ab ab d cde

LIMITS
    none

LIBRARY
    none

SEE ALSO
    XXX - fill in