Shortcuts

It allows to specify key characters for simplifying our expressions

\d digits ([0-9])

The expression:

$ grep -E "[0-9]{3,5}-[0-9]{4}-[0-9]{2,}-[0-9]{5}" file.txt

can be easily translated into:

$ grep -P "[\d]{3,5}-[\d]{4}-[\d]{2,}-[\d]{5}" file.txt

NOTE: we are using -P instead of -E flag because now we are using a Perl regular expression

let’s use this content in your file for tests

1stName
2ndName
Name1
Name2
LastName1
LastName2
Full Name
Change4Free
 Type
  your
   name

\b beginning

Finding expressions beginning with a number:

$ grep -P "\b[\d]" file.txt
1stName
2ndName

At the end:

$ grep -P "[\d]\b" file.txt
Name1
Name2
LastName1
LastName2

\s space

Finding expressions with spaces:

$ grep -P "\s" file.txt
Full Name
 Type
  your
   name

(?: GROUP )? Optional Group

Let’s validate ZIP codes, valid values are: 5_DIGITS 5_DIGITS-4_DIGITS

For this example we are going to replace the content of the file with:

12354
456465-444
54546-4445
5554
65465-9978

The expression that we need is:

$ grep -P "^[\d]{5}(?:-[\d]{4})?$" file.txt
12354
54546-4445
Where:
^               : at the beginning
[\d]{5}         : 5 digits
(?:REGEX)       : expression
?               : optional
$               : at the end

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