(1) You have too many slashes in that line, (2) the square brackets should either be balance or escaped, and (3) you are confusing "tr///" with "s///" -- only the latter takes a "g" modifier.

Figure out whether you are doing a string substitution (s///) or a character transliteration (tr///); use something besides "/" as the delimiter for the statement -- e.g. do  tr{x/z}{abc} or  s{a/c}{xyz}g; -- and if you are using s///, you have to use \[ to match a literal square bracket; any unescaped square brackets must be balanced, and should surround a set of characters that you intend to match at the given position in the regex.