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# 8. Command Execution

If a command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, the function is invoked as described in Functions. If there exists a shell builtin by that name, the builtin is invoked.

Otherwise, the shell searches each element of `$path` for a directory containing an executable file by that name. If the search is unsuccessful, the shell prints an error message and returns a nonzero exit status.

If execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script. `/bin/sh` is spawned to execute it. If the program is a file beginning with ``#!`', the remainder of the first line specifies an interpreter for the program. The shell will execute the specified interpreter on operating systems that do not handle this executable format in the kernel.

If no external command is found but a function `command_not_found_handler` exists the shell executes this function with all command line arguments. The function should return status zero if it successfully handled the command, or non-zero status if it failed. In the latter case the standard handling is applied: `command not found' is printed to standard error and the shell exits with status 127. Note that the handler is executed in a subshell forked to execute an external command, hence changes to directories, shell parameters, etc. have no effect on the main shell.

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This document was generated by Peter Stephenson on April, 2 2008 using texi2html 1.78.