Linux Learning-shell Verifying mailbox legitimacy with regular expressions

Citation: in today's era, email has become an important means of communication. e-mails to mentors, communication between academic studies, etc. Email is often used, but the verification of email is a little difficult, and here is an example of using Shell scripting under Linux.

Linux combines regular expressions with sed, gawk, and is a powerful feature. I said is true, did not deceive you, studies well.

Mailbox Verification
The basic format of the email address is:

username@hostname

1.username Partial pattern matching

The value of username can be in characters with a number of substrings and the following special characters:

• Point number
• Single Dash
• Plus
• Underline

In a valid email user name, these characters can appear in any combination.

The @ sign is preceded by the hostname section

^([a-zA-Z0-9_\-\.\+]+)

' ^ ': Indicates that the entire pattern starts with the characters in front of it
' + ': Indicates that the preceding character appears at least once
' [] ': Indicates that any combination of symbols in brackets is OK

2.hostname pattern Matching

The hostname part of the email address consists of a domain name and a server name. The server name and domain name are also subject to strict naming conventions, and only alphanumeric characters and the following special characters are allowed:

• Point number
• Underline

The server name and domain name are separated by a dot, specify the server name, followed by the subdomain name, and finally the top-level domain with no dot number behind it.

Hostname mode is the part after @

([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$

' $ ': Indicates the end of the character before it
([a-zA-Z0-9_\-\.]+)Can be matched by a
Server
Server.subdomain
Server.subdomain.subsomain

For top-level domains, there are some special rules. A top-level domain name can be only an alphabetic character and must be no less than two characters long and not exceed 5 characters in length. The following is the regular expression pattern used for the top-level domain:

\.([a-zA-Z]{2,5})$

Once together, the entire pattern is as follows:

^([a-zA-Z0-9_\-\.\+]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5})$

3. Writing Shell script files

Write the above code in the script, isemail.sh.

#!/bin/bash  # This file use to check email  echo   "Please input email:"  read  emailstr= ' echo   $email  | Gawk /^ ([a-za-z0-9_\-\.\+]+) @ ([a-za-z0-9_\-\.] +)\. ([a-za-z]{2,5}) $/{print $} '  ' if  [!-n  ' ${str}  "]then   echo   "validation is wrong."         else  echo   "Your Eamil is: ${str} "  fi   

Description: The above code by reading the user entered the mailbox, to determine whether the mailbox entered is legitimate. Finally, output two different prompts.

4. Testing

Reference

[1]linux command line and Shell script programming Daquan Second Edition

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Linux Learning-shell Verifying mailbox legitimacy with regular expressions