Regex

#!/bin/bash
pat='[\$a-zA-Z][a-zA-Z\d]*'
pat="${pat}(?:\.${pat})?"
fun=`echo "var b=a[0];a[0]=a[63%a.length];a[63]=b;" | sed "s@var\s($pat)=($pat)\[0\];\2\[0\]=\2\[(\d+)%\2\.length\];\2\[\3\]=\1;@\2=swap(\2,\3);@"`
echo $fun