regex_regular_expressions.md

one or other in list

(?:tom|jon)

when is Regex slow

string = 'aaaaazzzzzaaaaazaaaa'

# greedy (lazy) quatifier
\A(a.*)z
# =>  'aaaaazzzzzaaaaa'

# non-greedy quantifier
\A(a.*?)z
# => aaaa

this both are looping from end of the string till they find the point to stop. The difference is that greedy will stop at first occurence, while non-greedy is looping till he's sure that no other occurence exist

even wors is to do (.*)? which is like loop within a loop

so imagine now 10GB log file how would that screw your computer

Faster solution is to use negative, so search everything not matching and than actually match something

# www.fooooo.com
[^.]*\.(\w*)

Special thanx to tom for pointing this out

watch out for hyphen

[a-z]  # a till z in ascii table
[a_-]  # a or underscore or minus
[a_-*] # a or (_ till * in ascii table)