Regular Expression

• [^e-s0-5."] one of the characters inside the bracket.
• . any character except newline.
• \w any character in a word. [A-Za-z0-9_], \d digits, \s any whitespace: space, tab.

• Greedy: + one or more, * zero or more, ? zero or one
  • It matches greedily. It starts to match from the largest repetition of expression possible, and if it does not match the number of repetition is decreased by one.
• Lazy: +? one or more, *? zero or more, ?? zero or one
  • It starts to match with the smallest repetition of expression possible, and if it does not match the number of repetition is increased by one.
• Possesive (Java and Python 3.11+): ++, *+, ?+
  • It disables backing off, and matches as far as it can. If it does not match, the match fails.
• {n} n times, {n,} n times or more, {n,m} between n and m times
  • ? can be used for lazy search, and + for possesive search.

• (X) create group.
• \1, \2, … backreferences, match the content of n th group.
• (?>X) atomic grouping
  • The backtracking is diabled within the group.

• X(?=Y) match X if before Y
• X(?!Y) match X if not before Y
• (?<=Y)X match X if after Y
• (?<!Y)X match X if not after Y

• g global search
  • Look for multiple matches
• i ignore cases
• m multipline
  • ^ and $ matches the starts and ends of lines, instead of the start and end of the entire string.
• s single line (dotall)
  • . matches newline

Perl Compatible Regular Expression