What are common BRE metacharacters?

Common Basic Regular Expression (BRE) metacharacters include the following:

1. . (Dot): Matches any single character except a newline.

   • Example: a.b matches acb, a1b, etc.

2. ^ (Caret): Matches the beginning of a line.

   • Example: ^abc matches abc at the start of a line.

3. $ (Dollar Sign): Matches the end of a line.

   • Example: xyz$ matches xyz at the end of a line.

4. * (Asterisk): Matches zero or more occurrences of the preceding character or group.

   • Example: a* matches ``, a, aa, etc.

5. ? (Question Mark): Matches zero or one occurrence of the preceding character or group. (Note: In BRE, this must be escaped as \? to be treated as a metacharacter.)

   • Example: a\?b matches b or ab.

6. [ ] (Square Brackets): Matches any single character within the brackets.

   • Example: [abc] matches a, b, or c.

7. [^ ] (Negated Square Brackets): Matches any single character not within the brackets.

   • Example: [^abc] matches any character except a, b, or c.

8. {} (Curly Braces): Specifies a specific number of occurrences of the preceding character or group. (Note: In BRE, this must be escaped as \{ and \}.)

   • Example: a\{2\} matches aa.

9. ( ) (Parentheses): Groups patterns together. (Note: In BRE, this must be escaped as \( and \).)

   • Example: \(abc\) matches the exact string abc.

10. | (Pipe): Represents alternation (logical OR). (Note: In BRE, this must be escaped as \|.)

    • Example: abc\|def matches either abc or def.

Summary

These metacharacters allow for flexible pattern matching in BRE, but remember that some of them require escaping to function as intended.