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Shell builtin

From Wikipedia, the free encyclopedia

In computing, a shell builtin is a command or a function, called from a shell, that is executed directly in the shell itself, instead of an external executable program which the shell would load and execute.[1][2][3][4]

Shell builtins work significantly faster than external programs, because there is no program loading overhead. However, their code is inherently present in the shell, and thus modifying or updating them requires modifications to the shell. Therefore, shell builtins are usually used for simple, almost trivial, functions, such as text output. Because of the nature of some operating systems, some functions of the systems must necessarily be implemented as shell builtins. The most notable example is the cd command, which changes the working directory of the shell. Since each executable program runs in a separate process, and working directories are specific to each process, loading cd as an external program would not affect the working directory of the shell that loaded it.[5]

See also[edit]


  1. ^ POSIX standard: Shell Commands
  2. ^ Tansley, David (2000). "24. Shell built-in commands". Linux and Unix shell programming. Harlow: Addison-Wesley. ISBN 9780201674729.
  3. ^ Sobell, Mark G. (2003). "Built-ins". A Practical Guide to Red Hat Linux 8. pp. 161–162.
  4. ^ Albing, Carl; Vossen, JP; Newham, Cameron. "1.7. Using or Replacing Built-ins and External Commands". Bash Cookbook. O'Reilly Media. pp. 13–15. ISBN 9780596554705.
  5. ^ Kuhn, Darl; Kim, Charles; Lopuz, Bernard (2015). Linux and Solaris Recipes for Oracle DBAs (2nd ed.). Berkeley, CA: Apress. p. 47. ISBN 9781484212547.

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