Using Grep & Regular Expressions
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From Using Grep & Regular Expressions to Search for Text Patterns in Linux
Basic Usage
bash
$ grep [Pattern] [Input File]Print out every line in the file containing that Pattern
| Common Options | Description |
|---|---|
-i == --ignore-case | both upper- and lower-case variations |
-v == --invert-match | do not contain the Pattern |
-n == --line-number | show the line number |
A Little bit about Regular Expressions
Anchor Matches
| Anchor Matches | Description |
|---|---|
^ | at the begining of the string(line) |
$ | at the end of the string |
Matching Any Character
| Any Character | Description |
|---|---|
. | match any single character |
Bracket Expressions
- Characters between
[and]meansOR - But if the characters start with
^, it meansNOT, i.e. except - Represent a range of characters:
[A-Z], but we can use POSIX character classes to replace the[A-Z]:[[:upper:]]
Repeat Pattern Zero or More Times
| Character | Description |
|---|---|
* | repeat the previous character or expression zero or more times |
Escaping Meta-Characters
Using backslash character \ to escape characters that would normally have a special meaning.
Extended Regular Expressions
Use -E flag or call egrep command to use Extended Regular Expressions
Groupinn
Alternation
Quantifiers
| Character | Description |
|---|---|
? | match the previouscharacter zero or one times |
+ | one or more times |
Specifying Match Repetition
{NUM} to specify matching times, from an exact number, a range, or an upper or lower bounds