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= Exception Handling
Exceptions are rescued in a +begin+/+end+ block:
begin
# code that might raise
rescue
# handle exception
end
If you are inside a method, you do not need to use +begin+ or +end+ unless you
wish to limit the scope of rescued exceptions:
def my_method
# ...
rescue
# ...
end
The same is true for a +class+ or +module+.
You can assign the exception to a local variable by using <tt>=>
variable_name</tt> at the end of the +rescue+ line:
begin
# ...
rescue => exception
warn exception.message
raise # re-raise the current exception
end
By default, StandardError and its subclasses are rescued. You can rescue a
specific set of exception classes (and their subclasses) by listing them after
+rescue+:
begin
# ...
rescue ArgumentError, NameError
# handle ArgumentError or NameError
end
You may rescue different types of exceptions in different ways:
begin
# ...
rescue ArgumentError
# handle ArgumentError
rescue NameError
# handle NameError
rescue
# handle any StandardError
end
The exception is matched to the rescue section starting at the top, and matches
only once. If an ArgumentError is raised in the begin section, it will not be
handled in the StandardError section.
You may retry rescued exceptions:
begin
# ...
rescue
# do something that may change the result of the begin block
retry
end
Execution will resume at the start of the begin block, so be careful not to
create an infinite loop.
Inside a rescue block is the only valid location for +retry+, all other uses
will raise a SyntaxError. If you wish to retry a block iteration use +redo+.
See {Control Expressions}[rdoc-ref:syntax/control_expressions.rdoc] for
details.
To always run some code whether an exception was raised or not, use +ensure+:
begin
# ...
rescue
# ...
ensure
# this always runs
end
You may also run some code when an exception is not raised:
begin
# ...
rescue
# ...
else
# this runs only when no exception was raised
ensure
# ...
end
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