Simple Email Validator in Bash

email_validator_regex.sh

#!/usr/bin/env bash

#
# RFC standard of the email address could be found in rfc5322, rfc6854, etc.
#
# however, it is hard to escape all the special characters in the bash
# so, in this script, it will only check for the address syntax only
# having some valid/invalid inputs to test its result
#
# please be noted that, it is not design to detect mailbox deliverability
#

regex="^(([A-Za-z0-9]+((\.|\-|\_|\+)?[A-Za-z0-9]?)*[A-Za-z0-9]+)|[A-Za-z0-9]+)@(([A-Za-z0-9]+)+((\.|\-|\_)?([A-Za-z0-9]+)+)*)+\.([A-Za-z]{2,})+$"

valid_inputs=(
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "valid+1@ex_ample.com"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "valid+01@ex_ample.com"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "valid@e-x_ample.com"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
)

invalid_inputs=(
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "inv [email protected]"
  "invalid@exa mple.com"
  "[email protected]"
  "invalid@_"
  "invalid@com"
  "[email protected]"
  "invalid@example._com"
  "invalid@e-x._ample.com"
  "[email protected]_ample.com"
  "[email protected]_ample.com"
  "[email protected]"
  "invalid@example._"
  "[email protected]"
  "invalid@example.+"
  "[email protected]"
  "[email protected]"
  "[email protected]"
  "invalid@example."
  "[email protected]."
  "[email protected]"
  "[email protected]"
  "invalid@_.com"
  "[email protected]"
  "invalid@com"
  "[email protected]"
  "invalid@+com"
  "invalid@-com"
  "invalid@_com"
  "invalid@."
  "invalid@_"
  "invalid@-"
  "[email protected]"
  "@"
  ".@."
  "-@-"
  "_@_"
  "+@+"
  "a.@.."
  "@com"
  "@example.com"
  "[email protected]"
  "[email protected]"
  "invalid@_123.com"
  "[email protected]"
  "[email protected]"
)

function validator {
  if [[ $1 =~ ${regex} ]]; then
    printf "* %-48s \e[1;32m[pass]\e[m\n" "${1}"
  else
    printf "* %-48s \e[1;31m[fail]\e[m\n" "${1}"
  fi
}

cat <<-EOF
a simple email address validator in bash

online validator: http://emailregex.com/

RFC Standards for email address
- https://tools.ietf.org/html/rfc821
- https://tools.ietf.org/html/rfc5322
- https://tools.ietf.org/html/rfc6854
- https://tools.ietf.org/html/rfc5321
- https://tools.ietf.org/html/rfc5322#section-3.4

References:
- http://emailregex.com/email-validation-summary/
EOF

echo
echo "### expected result: valid"
echo

for input in "${valid_inputs[@]}"; do
  validator "${input}"
done

echo
echo "### expected result: invalid"
echo

for input in "${invalid_inputs[@]}"; do
  validator "${input}"
done

I had hoped to find a true validator - along these lines. If you ever want to go that way, here is a start.

This regex is failing for the following email addresses which are VALID email addresses -
[email protected]
[email protected]
[email protected]

Any of the below regex works fine for all the test cases mentioned in your sh file as well as the email addresses I mentioned above -
^([A-Za-z]+[A-Za-z0-9]*((\.|\-|\_)?[A-Za-z]+[A-Za-z0-9]*){0,})@(([A-Za-z]+[A-Za-z0-9]*)+((\.|\-|\_)?([A-Za-z]+[A-Za-z0-9]*)+){0,})+\.([A-Za-z]{2,})+$
OR
^([A-Za-z]+[A-Za-z0-9]*((\.|\-|\_)?[A-Za-z]+[A-Za-z0-9]*)*)@(([A-Za-z]+[A-Za-z0-9]*)+((\.|\-|\_)?([A-Za-z]+[A-Za-z0-9]*)+)*)+\.([A-Za-z]{2,})+$

@anujatupe thanks

I've fixed those problems and added more test cases, please have a look at the updated version.

@Biep indeed, having validation for the MX records would be better. Even more with NS records check.
But the script here is focus on the format, but not availability.

the code is failing on [email protected] . Looks like it is failing on a dash followed by number -01.

@dnicolaev thanks for report. I've update the script and add more test cases.

let's work again ;-)
now it is failing on this [email protected]

ps: Thank you for doing this. I really appreciate this tool.

@dnicolaev big thanks for hunting bugs in this script.

I've do some research for the RFC standards, and script updated.
please have a look for the latest script again.

the code is failing on this [email protected]

thanks this is too good it's very helpful

I have a question on a different problem for validation fo password
you have any pattern for that

@suraj9741 I've made some fixes for the validation rules according to the RFC standards.
but the address [email protected] is actually a valid address,
please have a look at the RFC standard definition. (RFC-5322, section 3.4 and section 3.4.1).

as for the part of password validation,
I think there's no validator available out there, password could in any character, in any format, isn't it?

@guessi according to this, you can have a valid email address with multiple @ characters in it.

@phpmoli interesting fact, but I'd prefer not to change this script for now. for the normal use case, we don't use multiple "@" in email address?

anyway, thanks for let me know 👍

Hey guys this is nice code :-) i find another bug :-)

He report this is wrong e-mail :-)
[email protected]
[email protected]
[email protected]

Best Regards
TaKeN

invalid@user_in_domain.com is showing up as valid.

this fixed the problem:
regex="^(([A-Za-z0-9]+((.|-|_|+)?[A-Za-z0-9]?)[A-Za-z0-9]+)|[A-Za-z0-9]+)@(([A-Za-z0-9]+)+((.|-)?([A-Za-z0-9]+)+))+.([A-Za-z]{2,})+$"