enh(autodetect) fewer false positives on variables

For languages with $ident and @Ident style variables this attempts
to prevent positives for $ident$ and @Ident@ type expressions, which
are likely something else entirely.

- bash
- perl
- php
- ruby

Author: joshgoebel

src/languages/bash.js

@@ -6,6 +6,8 @@ Website: https://www.gnu.org/software/bash/
 Category: common
 */
 
+import * as regex from '../lib/regex.js';
+
 /** @type LanguageFn */
 export default function(hljs) {
   const VAR = {};
@@ -23,7 +25,7 @@ export default function(hljs) {
   Object.assign(VAR,{
     className: 'variable',
     variants: [
-      {begin: /\$[\w\d#@][\w\d_]*/},
+      {begin: regex.concat(/\$[\w\d#@][\w\d_]*/, `(?![\\w\\d])(?![$])`) },
       BRACED_VAR
     ]
   });

src/languages/perl.js

@@ -5,6 +5,9 @@ Website: https://www.perl.org
 Category: common
 */
 
+import * as regex from '../lib/regex.js';
+
+/** @type LanguageFn */
 export default function(hljs) {
   var PERL_KEYWORDS = {
     $pattern: /[\w.]+/,
@@ -40,7 +43,12 @@ export default function(hljs) {
   var VAR = {
     variants: [
       {begin: /\$\d/},
-      {begin: /[$%@](\^\w\b|#\w+(::\w+)*|\{\w+\}|\w+(::\w*)*)/},
+      {begin: regex.concat(
+        /[$%@](\^\w\b|#\w+(::\w+)*|\{\w+\}|\w+(::\w*)*)/,
+        // negative look-ahead tries to avoid matching patterns that are not
+        // Perl at all like $ident$, @ident@, etc.
+        `(?![A-Za-z])(?![@$%])`
+        )},
       {begin: /[$%@][^\s\w{]/, relevance: 0}
     ]
   };

src/languages/php.js

@@ -13,7 +13,7 @@ Category: common
 export default function(hljs) {
   const VARIABLE = {
     className: 'variable',
-    begin: '\\$+[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'
+    begin: '\\$+[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*' + `(?![A-Za-z0-9])(?![$])`
   };
   const PREPROCESSOR = {
     className: 'meta',

src/languages/ruby.js

@@ -160,8 +160,10 @@ export default function(hljs) {
     },
     NUMBER,
     {
+      // negative-look forward attemps to prevent false matches like:
+      // @ident@ or $ident$ that might indicate this is not ruby at all
       className: "variable",
-      begin: '(\\$\\W)|((\\$|@@?)(\\w+))' // variables
+      begin: '(\\$\\W)|((\\$|@@?)(\\w+))(?=[^@$?])' + `(?![A-Za-z])(?![@$?'])`
     },
     {
       className: 'params',