The initial argument for these functions is the pathname of a file which is to be executed.
The Fa const char *arg and subsequent ellipses in the Fn execl , Fn execlp , and Fn execle functions can be thought of as arg0 arg1 ..., argn Together they describe a list of one or more pointers to null-terminated strings that represent the argument list available to the executed program. The first argument, by convention, should point to the file name associated with the file being executed. The list of arguments must be terminated by a NULL pointer.
The Fn exect , Fn execv , and Fn execvp functions provide an array of pointers to null-terminated strings that represent the argument list available to the new program. The first argument, by convention, should point to the file name associated with the file begin executed. The array of pointers must be terminated by a NULL pointer.
The Fn execle and Fn exect functions also specify the environment of the executed process by following the NULL pointer that terminates the list of arguments in the parameter list or the pointer to the argv array with an additional parameter. This additional parameter is an array of pointers to null-terminated strings and must be terminated by a NULL pointer. The other functions take the environment for the new process image from the external variable environ in the current process.
Some of these functions have special semantics.
The functions Fn execlp and Fn execvp will duplicate the actions of the shell in searching for an executable file if the specified file name does not contain a slash ``/ '' character. The search path is the path specified in the environment by ``PATH '' variable. If this variable isn't specified, the default path ``/bin:/usr/bin: '' is used. In addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve returned Er EACCES ) , these functions will continue searching the rest of the search path. If no other file is found, however, they will return with the global variable errno set to Er EACCES .
If the header of a file isn't recognized (the attempted execve returned Er ENOEXEC ) , these functions will execute the shell with the path of the file as its first argument. (If this attempt fails, no further searching is done.)
If the file is currently busy (the attempted execve returned Er ETXTBUSY ) , these functions will sleep for several seconds, periodically re-attempting to execute the file.
The function Fn exect executes a file with the program tracing facilities enabled (see ptrace(2)).
Fn Exect and Fn execv may fail and set errno for any of the errors specified for the library function execve(2).
The behavior of Fn execlp and Fn execvp when errors occur while attempting to execute the file is historic practice, but has not traditionally been documented and is not specified by the POSIX standard.
Traditionally, the functions Fn execlp and Fn execvp ignored all errors except for the ones described above and Er ENOMEM and Er E2BIG , upon which they returned. They now return if any error other than the ones described above occurs.