help with regex pattern

-Dman100-
-Dman100- used Ask the Experts™
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I'm terrible with regular expressions and cannot figure out how to use a regex expression to check for the following pattern.

The first 3 characters must be alpabetic and the next 7 characters must be numeric.

The first 3 characters can only be:
RTN
ADJ
TRA

The remaining 7 characters can be any numeric value 0-9

I'm sure this is simple, but I can't figure it out.

I was starting with this:
[A-Za-z][A-Za-z][A-Za-z][0-9] but, this isn't even close.

Thanks for any help.
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ǩa̹̼͍̓̂ͪͤͭ̓u͈̳̟͕̬ͩ͂̌͌̾̀ͪf̭̤͉̅̋͛͂̓͛̈m̩̘̱̃e͙̳͊̑̂ͦ̌ͯ̚d͋̋ͧ̑ͯ͛̉Glanced up at my screen and thought I had coded the Matrix...  Turns out, I just fell asleep on the keyboard.
Most Valuable Expert 2011
Top Expert 2015

Commented:
Actually, it is close--it's just not finished  = )

I believe you just need to repeat the digit part 6 more times:

[A-Za-z][A-Za-z][A-Za-z][0-9][0-9][0-9][0-9][0-9][0-9][0-9]

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However, if you can tell us what language or editor you are using, we might be able to shorten it a bit. For example, you might be able to use:

[A-Za-z]{3}[0-9]{7}

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Also, you may need some boundaries on that pattern to prevent matching substrings. Start of string ( ^ ) and end of string ( $ ) are fairly common among languages/editors:

^[A-Za-z][A-Za-z][A-Za-z][0-9][0-9][0-9][0-9][0-9][0-9][0-9]$

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Top Expert 2011

Commented:
Please try the following pattern:

^((RTN)|(ADJ)|(TRA))\d{7}$
ǩa̹̼͍̓̂ͪͤͭ̓u͈̳̟͕̬ͩ͂̌͌̾̀ͪf̭̤͉̅̋͛͂̓͛̈m̩̘̱̃e͙̳͊̑̂ͦ̌ͯ̚d͋̋ͧ̑ͯ͛̉Glanced up at my screen and thought I had coded the Matrix...  Turns out, I just fell asleep on the keyboard.
Most Valuable Expert 2011
Top Expert 2015

Commented:
Ah, I missed the restriction on the letters. Silly me  : \
Software Engineer
Commented:
You don't need the extra parenthesis

^(RTN|ADJ|TRA)\d{7}$

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HonorGodSoftware Engineer

Commented:
wdosanjos provided the 1st answer, I just simplified it.

Please "request attention" and have them reopen it so that you can give most of the points to wdosanjos.

Thanks!

Good luck & have a super day.

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