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Command exit status

Commands can be executed in expressions and their exit status returned by enclosing them in braces (`{}'). Remember that the braces should be separated from the words of the command by spaces. Command executions succeed, returning true, i.e. `1', if the command exits with status 0, otherwise they fail, returning false, i.e. `0'. If more detailed status information is required then the command should be executed outside of an expression and the status shell variable examined.

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