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Conditional Control Flow
Commands that complete successfully exit with status zero; all non-zero exit statuses indicate failure. Conventionally, a status of 1 is used as the generic program error status, and 2 indicates user error (such as invalid input or arguments), but any value in the range of 0-127 may be used. On many systems, statuses 128-255 have special meaning (such as signal reporting) and should not be set. The exit status of the last process in a pipeline is used as the status for the entire pipeline.
The success or failure of a pipeline may be used to run additional pipelines:
rm some-file && echo success || echo failure
Pipelines chained in this way are known as "lists" and have left-to-right precedence, such that the above will always either echo success or failure, but never both. Most commonly, AND sequences are chained together so that a series of tasks can proceed only if every task before it was successful:
task1 && task2 && task3
If semicolons were used instead (or if each task were on its own line), then the tasks would run regardless of whether the previous tasks failed.
Example
All material is licensed under the Apache License Version 2.0, January 2004.
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