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

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,})+$"