11/25/2023 0 Comments What does pf ef linux commandIn the second case, true exits with a code of 0 $ trueĪnd therefore echo foo is not executed, then echo bar is executed. Which means echo foo does not run (i.e., shortcircuiting echo foo). In the first case, the false is a command that exits with the status of 1 $ false For example, both of the followingĬommands write solely bar to standard output: $ false & echo foo || echo bar The operators "&" and "||" shall have equal precedence and shall beĮvaluated with left associativity. Operators ' ' and '&' and optionally terminated by ' ', '&', or The terminal outputs the results of commands which are specified by the user itself. This includes package installation, file manipulation, and user management. As the docs say:Īn AND-OR list is a sequence of one or more pipelines separated by theĪ list is a sequence of one or more AND-OR lists separated by the The terminal can be used to accomplish all Administrative tasks. Grammar symbols, quoted from the documentation: %token AND_IF OR_IF DSEMIĪnd the Grammar (also quoted from the documentation), which shows that any number of AND_IFs ( &) and/or OR_IFs ( ||) can be be strung together (as and_or is defined recursively): and_or : pipelineīoth operators have equal precedence and are evaluated left to right (they are left associative). The & is referred to as AND_IF in the posix shell grammar, which is part of an and_or list of commands, which also include the || which is an OR_IF with similar semantics. ![]() ![]() This allows a limited amount of communication between processes. They should return 0 if they exit successfully, or greater than zero if they do not. Your shell considers a return value of 0 for true, other positive numbers for false Not all programs have the same behavior, so for this to work, you need to understand what the program considers a "failure" and how it handles it by reading the documentation and, if necessary, the source code. You may notice I've used the word "intent" - that's for good reason. ![]() It intends to prevent the running of the second process if the first fails. This is idiomatic of Posix shells, and not only found in Bash. The intent is to execute the command that follows the & only if the first command is successful. In shell, when you see $ command one & command two
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