gsub(r,s)                    global substitution

    Substitute s for strings matched by r globally in $0.  Return number of
    substitutions made.   The operator '$$0'  or the character  '&' will be
    replaced in the substitution string by the the sub-string matched.  For
    Example:

    $0 = "The occurrence of any filename"

    gsub(/\s+/,"\t") ==> $0 = "The\toccurrence\tof\tany\tfilename"

gsub(r,s,t)                  global substitution

    Substitute s for strings matched by  r globally in t. Return number  of
    substitutions made.   The operator '$$0'  or the character  '&' will be
    replaced in the substitution string by the the sub-string matched.  For
    example to remove punctuation and parenthesis:

    t = "The best, of which he was capable, (considering";

    gsub(/({_p}|{_b})+/,"",t)
      ==> t == "The best of which he was capable considering"