Add a regular expression engine

[vinc]

Add a very basic regular expression engine based on https://www.cs.princeton.edu/courses/archive/spr09/cos333/beautiful.html

• Support . char
• Support * char
• Support + char
• Support ? char
• Support \ char
• Support | char
• Support \d chars
• Support \D chars
• Support \s chars
• Support \S chars
• Support \w chars
• Support \W chars
• Support {a,b} range
• Support lazy ? char

Also add a find --line command that works like grep on Unix to test it on files.

[vinc]

The first command using the regex engine will be find used to find files with a given name or lines in files with a given pattern:

> find /tmp --name ".*txt" --line "exa\w+ple"

Or with the shortcut form:

> f /tmp -n "*.txt" -l "exa\w+ple"

The first parameter --name is like the find command in Unix and the second parameter --line is like grep.

[vinc]

Finding Alice and cat in the example text:

Now we probably need to add greedy matching to find cats?

[vinc]

The find --name part of the find command will be added in another PR with the Wildcard struct.

[vinc]

Recursive line matching: