1. The order of precedence of operators in POSIX extended regular expression is as follows.

   1. Collation-related bracket symbols [==], [::], [..]
   2. Escaped characters \
   3. Character set (bracket expression) []
   4. Grouping ()
   5. Single-character-ERE duplication *, +, ?, {m,n}
   6. Concatenation
   7. Anchoring ^, $
   8. Alternation |

2. Some regular expression patterns are defined using a single leading backslash, e.g., \s, \b, etc. However, since special …

The article 14 Practical examples of the grep command has some good examples on how to use the grep command.

1. The Perl style (option -P) regular expression is more powerful than the basic (default) and extended (option -E) regular expression. It is suggested that you use the perl style as …