title: awk field separator with regexp lookahead or lookbehind
body: <p>I want to split line with escape sequence but failed. For example:</p>
  
  <pre><code>$ echo "1,2\,2,333"|awk -F "(?&lt;\!\\,)," '{print $2}'   ## expecting "2\,2"
  awk: warning: escape sequence `\!' treated as plain `!'
  awk: warning: escape sequence `\,' treated as plain `,'
  </code></pre>
  
  <p>Does awk/gawk support field separator with regexp lookahead or lookbehind ?</p>