While-Loop BASH-Regex not matching - regex

Question

Why is this INCREDIBALLY simple REGEX not matching?!!?
#!/bin/bash
while true
do
read -r -p $'What is the JIRA Ticket associated with this work?' JIRA
#Use a regular expresion to verify that our reply stored in JIRA is only 4 digits, if not, loop and try again.
if [[ ! "$JIRA" =~ [0-9]{4} ]]
then
echo -en "The JIRA Ticket should only be 4 digits\nPlease try again."
continue
else
break 1
fi
done
When prompted, if you type "ffffff" it catches, but if you type more than 4 digits "444444" or even toss a letter in there "4444444fffff" it catches nothing, hits the else block and quits. I think this is basic and I'm dumbfounded as to why its not catching the extra digits or characters?
I appreciate the help.

Answer 1

You need to change your equality test to:
if [[ ! "$JIRA" =~ ^[0-9]{4}$ ]]
This ensures that the entire string contains just four digits. ^ means beginning of string, $ means end of string.

Answer 2

The regular expression is open-ended, meaning it only has to match a substring of the left-hand argument, not the entire thing. Anchor your regular expression to force it to match the entire string:
if [[ ! "$JIRA" =~ ^[0-9]{4}$ ]]

Answer 3

Maybe a simpler pattern (== instead of =~) may solve your issue:
#!/bin/bash
while true
do
read -r -p $'What is the JIRA Ticket associated with this work?' JIRA
[[ $JIRA == [0-9][0-9][0-9][0-9] ]] && break 1
echo -en "The JIRA Ticket should only be 4 digits\nPlease try again."
done