Bars and Repetition

The common bar line is represented with a pipe symbol, |.
Here’s an example, 2 notes, a bar and two other notes:


Double bar can are formed with a combination of pipe (|) and square brackets ([ or ]).

|]	thin-thick double bar line
||	thin-thin double bar line
[|	thick-thin double bar line

Here’s how it looks like in context:

X: 1
C2 [| D2 || E2 |]

Of course bars are also used to indicate repeated parts. In this case the colon symbol is used:

|:     start of repeated section
:|.    end of repeated section
::     start & end of two repeated sections

1[ and 2[ are used to represent first and second repeat.
When adjacent to other bar symbols, they can be shortened to |1 and :|2.

1[     first repeat
2[     second repeat
|1     bar and first repeat
:|2    bar and second repeat

Here is a simple example:

X: 1
|: CD EF | FE |1 DC :|2 CC :|

For a more detailed explanation of bars and repeats, see the offical ABC website.