Linux Basics (10) on the difference between grep and egrep

What is the difference between an extended regular expression and a regular expression when egrep or Grep-e uses an extended regular expression for text matching compared to grep?

1 Basic Regular Expressions:

Character Matching:

.: Any single character

[]: A single character in a character set such as [0-9] means any number of digits

[^]: a single character that is not part of a character set such as [^[:space:]] denotes any non-whitespace character

Number of matches:

*: Any time

\?: 0 or 1 times

\{m,n\}: At least m times, up to n times;

. *: Any character of any length

Anchoring:

^: Anchor at the beginning of the line

$: End of line anchoring

\<, \b: The head of the word

\>, \b: suffix

Tuple references:

\(\)

\1, \2, \3, ...

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2. Extended Regular Expressions

Character Matching:

.

[]

[^]

Number of matches:

*: Match the preceding character any number of times

?: matches the preceding character 0 or 1 times

+: Match the characters in front of it at least 1 times

{M,n} matches the preceding character at least m times, up to n times note: No more escaping than basic regular expressions

Location anchoring:

^ Beginning of the line

$ End of line

\< or \b # # # # words First

\> or ###\b ending

Meta-group:

(): Tuple Note: You do not need to escape from a basic regular expression

\1, \2, \3, ...

Or

|: OR

Note: This is a function of extended regular expressions. To grep support, you must use the GREP-E

Note: The content used for selection must be added to the parentheses

(c|c) At:cat or cat

C|cat:c or Cat

By comparison, the difference between a basic regular expression and an extended regular expression is that

1. On the number of matches, the extended regular expression is more than one + to match the preceding character at least once the equivalent of \{1,\}

2. Extended regular Expression {M,n} no longer needs to be escaped

3. Grouping of Extended regular expressions () also no longer needs to be escaped

4. Regular expressions have one more or |

Then we can consider using extended regular expressions when matching text patterns, avoiding the use of too many escape characters \

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Linux Basics (10) on the difference between grep and egrep