Shell Programming and Scripting

function getTime(time)
{
        print time;
        time = gsub(":","x",time);
        print time;
}

       gsub(r, s [, t])        For each substring matching the regular expression r in the
                               string t, substitute the string s, and return the number of
                               substitutions.   If t is not supplied, use $0.  An & in the
                               replacement text is replaced with the text that  was  actu*
                               ally  matched.   Use  \& to get a literal &.  (This must be
                               typed as "\\&"; see GAWK: Effective AWK Programming  for  a
                               fuller  discussion  of the rules for &'s and backslashes in
                               the replacement text of sub(), gsub(), and gensub().)

man awk

info awk