I have a Regex to allow alphanumeric, underscore and dots but not consecutive dots:
^(?!.*?[.]{2})[a-zA-Z0-9_.]+$
I also need to now allow dots in the first and last character of the string.
How can I do this?
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3 Answers
You can use it like this with additional lookaheads:
^(?!\.)(?!.*\.$)(?!.*\.\.)[a-zA-Z0-9_.]+$
(?!\.)- don't allow.at start(?!.*\.\.)- don't allow 2 consecutive dots(?!.*\.$)- don't allow.at end
9 Comments
nozzleman
just want to point out that this can be written shorter like
^(?!\.)(?!.*\.$)(?!.*?\.\.)[\w.]+$
anubhava
Yes indeed
\w is shortcut for [[a-zA-Z0-9_] in many regex flavors but not supported in awk, sed etc.
Sufian
And to disallow string starting with a digit, I added
(?!\d) to make the regex: ^(?!\d)(?!\.)(?!.*\.$)(?!.*?\.\.)[a-zA-Z0-9_.]+$. Thanks for the breakdown of each regex portion. :)anubhava
use
preg_match("/^(?!\.)(?!.*\.$)(?!.*?\.\.)[a-zA-Z0-9_.]+$/", $number, $m); and them print $m[0]
Shailendra Madda
I am using this regex in android but still allowing dot at the start
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Re-write the regex as
^[a-zA-Z0-9_]+(?:\.[a-zA-Z0-9_]+)*$
or (in case your regex flavor is ECMAScript compliant where \w = [a-zA-Z0-9_]):
^\w+(?:\.\w+)*$
See the regex demo
Details:
^- start of string[a-zA-Z0-9_]+- 1 or more word chars(?:\.[a-zA-Z0-9_]+)*- zero or more sequences of:\.- a dot[a-zA-Z0-9_]+- 1 or more word chars
$- end of string
answered Nov 21, 2016 at 11:20
Wiktor Stribiżew
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Comments
You can try this:
^(?!.*\.\.)[A-Za-z0-9_.]+$
This will not allow any consecutive dots in the string and will also allow dot as first and last character
