# Binary String pattern matching

kuna.prime kuna.prime@REDACTED
Wed Dec 9 19:58:21 CET 2020

```HI,

first of all binary string is of form <<"3123CHF">> and not <<3123CHF>> i'm just stating it in case there was a mistake in the first mail

to answer your questio in order to pattern match you need to know the size of field you are matching so

<<X:4/binary, "CHF">> = <<"3123CHF">>.

will match fist 4 bytes and interpret that as new binary (X).

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Wednesday, December 9, 2020 7:28 PM, Java House <java4dev@REDACTED> wrote:

> there is a typo in the example
> currrency_to_credits({cur, << Value , "CHF">>}, Acc)
> when Value >= <<"1000">>, Value =< <<"10000">> ->
> {chf, Acc + Value };
> currrency_to_credits({cur, << Value , "EUR">>}, Acc)
> when Value >= <<"1000">>, Value =< <<"10000">> ->
> {eur, Acc + Value };
> currrency_to_credits({cur, << Value , "US">>}, Acc)
> when Value >= <<"1000">>, Value =< <<"10000">> ->
> {us, Acc + Value };
>
> Στις Τετ, 9 Δεκ 2020 στις 7:17 μ.μ., ο/η Java House <java4dev@REDACTED> έγραψε:
>
>> Hello all
>>
>> I am learning Erlang and have stuck to the following problem.
>> How to write a function with pattern matching when the parameter is a binary string.
>>
>> I have a list of binary strings e.g.
>> <<3123CHF>>
>> <<341424343EUR>>
>> <<14143US>>
>>
>> I am trying to create a function that matches according to a pattern.
>>
>> currrency_to_credits({cur, <<A, "CHF">>}, Acc)
>> when Value >= <<"1000">>, Value =< <<"10000">> ->
>> {chf, Acc + A};
>> currrency_to_credits({cur, <<A, "EUR">>}, Acc)
>> when Value >= <<"1000">>, Value =< <<"10000">> ->
>> {eur, Acc + A};
>> currrency_to_credits({cur, <<A, "US">>}, Acc)
>> when Value >= <<"1000">>, Value =< <<"10000">> ->
>> {us, Acc + A};
>>
>> But this does not seem to be the right way.
>> How can I create a pattern for binary string?
>> will it work better for list string? How?
>>
>> Thank you
>> Nikolas
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