Regex
regex - From Pattern to Pattern
| Pattern | regex |
|---|---|
from a to z | [a-z] |
from A to Z | [A-Z] |
from a to z and A to z | [a-zA-Z] |
from 0 to 9 | [0-9] |
a or b or c | [abc] |
Except d or e | [^de] |
regex - How many times
| Occurs | regex |
|---|---|
0 or 1 times | [ ]? |
0 or more times | [ ]* |
1 or more time | [ ]+ |
n times | [ ]{n} |
n or more times | [ ]{n,} |
Minimum p times and Maximum q times | [ ]{p,q} |
regex - Meta characters
| Meta Character | regex | Explain |
|---|---|---|
\d | [0-9] | Digit 1 to 9 - Only One digit matching |
\D | [^0-9] | Not a digit |
\w | [a-zA-Z_0-9] | Word containing characters a to z, A to Z, 0 to 9 and _ |
\W | [^\w] | Not a word character |
\s | [\s] | Whitespaces - spaces, tab, newline |
\S | [\S] | Not Whitespaces |
\b | [\b] | Word boundary |
\B | [\B] | Not a word boundary |
^ | [^] | Beginning of a string |
$ | Hello[$] | Ending of the string |
| | | [a|b] | Either or - a or b |
() | (,|-) | Capture GROUP - these are grouped and retrieved with in the expression |
regex - email
[a-zA-Z0-9+_.-]+@[a-zA-Z0-9.-]+
regex - sample
Example to test the working of regex:
emails.txt
[email protected]
lkjsdlf lskjdfl kjasdf [email protected]
av12_name.com
[email protected]
[email protected]
[email protected]
grep emails from emails.txt
grep -oP '[a-zA-Z0-9+_.-]+@[a-zA-Z0-9.-]+' emails.txt
regex - phone
regex - phone - no grouping - basic
phone.txt
123 456 7899
123.456.7899
(123).456.7899
123-456-7899
No grouping and basic - also observe \s, try placement of \s in [\s.-]
grep -oP '[0-9]{3}[\s.-][0-9]{3}[.|\-|\s][0-9]{4}' phones.txt
output of phone
123 456 7899
123.456.7899
123-456-7899
regex - phone - no grouping - simplify
No grouping and simple
grep -oP '[\d]{3}[\s.-][\d]{3}[\s.-][\d]{4}' phones.txt
regex - grouping
Group implementation
grep -oP '([\d]{3}[\s|\.|\-]){2}[\d]{4}' phones.txt
regex - extracting all phone numbers
grep -oP '(\(?[\d]{3}\)?[\s|\.|\-]){2}[\d]{4}' phones.txt
regex - Build and test
Build and test your regex at : regex101