Binaries and Pattern Matching

The first rule of binaries is, “If in doubt, specify the type of each field.” Available types are binary, bits, bitstring, bytes, float, integer, utf8, utf16, and utf32. We can also add qualifiers:

• size(n) qualifies the size of the field, in bits.
• signed and unsigned qualifiy integer fields as signed or unsigned.
• The endianness qualifiers are big, little and native.

We use hyphens to separate multiple attributes of a field as follows: << length::unsigned-integer-size(12), flags::bitstring-size(4) >> = data.

However, unless we’re doing a lot of work with binary file or protocol formats, the most common use of all this scary stuff is to process UTF-8 strings.

String processing with binaries

When we process lists, we use patterns that split the head from the rest of the list. With binaries that hold strings, we can do the same kind of trick. We have to specify the type of the head (UTF-8), and make sure the tail remains a binary.

Below is an example that’ll produce the following result:

8706
111
103

Click the “Run” button to execute the code below.