How does the 'egrep' command differ from 'grep'?

The 'egrep' command is a variant of the 'grep' command specifically designed to support extended regular expressions (ERE). This means that 'egrep' allows for more advanced pattern matching features than the standard 'grep', which operates with basic regular expressions (BRE).

In the context of using these commands, 'egrep' enables the use of characters and features such as the vertical bar '|' for alternation and grouping with parentheses, which would otherwise require escaping in 'grep'. For instance, using 'egrep', you could search for patterns like 'cat|dog' without needing to escape the '|' character, simplifying the syntax for complex pattern searches.

Furthermore, the difference does not reside in performance since both commands are generally optimized for similar tasks, nor does 'egrep' lack support for file input, as both commands can process files as well.