Regular Expression for string pattern

Question

I am new to regular expressions. I am looking for String which can have only characters 'SALT' which is prefixed by + or – sign.

I am using [(SALT){1}\+-]{8} which is partially working. Not completely.

Total characters 8

Acceptable values

+S+A+L+T

+S-A-L+T

+T+L+A+S

These are the following values which are not acceptable.

No repeat of characters except +,- as a prefix only.

i.e

S+L+S+S ( Character is repeated in this )
S+++++ 
-------S
S-+S-+S

I would appreciate if anyone help me in this regard.

Thanks

"No repeat of characters" is a difficult requirement for a regex. It usually ends messy. — Bernhard Barker
– Bernhard Barker, Commented Apr 26, 2013 at 20:40
For a start, read the basic syntax manual again.[(SALT)] is a character class; it matches a single character which can be a literal ( or S or A or ... — tripleee
– tripleee, Commented Apr 26, 2013 at 20:43
@Dukeling Well if there are only four characters, (s)he could do a negative lookahead / negative lookbehind for each of them. I agree though. — Darko Kenda
– Darko Kenda, Commented Apr 26, 2013 at 20:44
There are different regex flavors. If a Perl regular expression is acceptable, it makes this a lot easier (or, at least vaguely possible) than if you are restricted to traditional basic or extended regular expressions. — tripleee
– tripleee, Commented Apr 26, 2013 at 20:46

Explosion Pills · Accepted Answer · 2013-04-26 20:45:37Z

5

You can use lookaheads to make sure all of your characters are there

^(?=.*S)(?=.*A)(?=.*L)(?=.*T)([+-][SALT]){4}$

answered Apr 26, 2013 at 20:45

Explosion Pills

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4 Comments

tripleee Over a year ago

... provided your platform's regex support is Perl compatible.

Explosion Pills Over a year ago

@CasimiretHippolyte why do you say that?

Bernhard Barker Over a year ago

@ExplosionPills Because the first character must be a + or -, but it doesn't make a big difference.

user2325283 Over a year ago

The above answer works for me. thanks for overwhelming response for this question.

Casimir et Hippolyte · Accepted Answer · 2013-04-26 21:11:13Z

0

A funny way (if the RE engine supports conditionnals and backreferences) :

^(?:[+-](?:(S(?(1)Z))|(A(?(2)Z))|(L(?(3)Z))|(T(?(4)Z)))){4}$

answered Apr 26, 2013 at 21:11

Casimir et Hippolyte

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Comments

Jerry · Accepted Answer · 2013-04-26 21:11:58Z

-1

Try this:

^(([+\-]([SALT]))(?!\2))+$

It uses negative lookahead assertion to prevent matching repeating ones.

edited Apr 26, 2013 at 21:11

answered Apr 26, 2013 at 20:44

Jerry

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3 Comments

Blender Over a year ago

This will match SSSSSSSSSSSSSSSSSSSSSSSS...

Blender Over a year ago

+S+S-S+S-S+S. It won't prevent duplicates.

tripleee Over a year ago

Still would allow -S-A-A-A.

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