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%sccs.include.redist.man%
@(#)exec.3 6.3 (Berkeley) 02/23/91
extern char **environ; execl(const char *path, const char *arg, ...); execlp(const char *file, const char *arg, ...); execle(const char *path, const char *arg, ..., char *const envp[]); exect(const char *path, char *const argv[], char *const envp[]); execv(const char *path, char *const argv[]); execvp(const char *file, char *const argv[]);
The initial argument for these functions is the pathname of a file which is to be executed.
The ``const char *arg'' and subsequent ellipses in the execl , execlp , and 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 exect , execv , and 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 execle and 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 execlp and 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 addtion, certain errors are treated specially.
If permission is denied for a file (the attempted execve returned EACCES), these functions will continue searching the rest of the search path. If no other file is found, however, they will return with errno set to EACCES.
If the header of a file isn't recognized (the attempted execve returned 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 ETXTBUSY), these functions will sleep for several seconds, periodically re-attempting to execute the file.
The function exect executes a file with the program tracing facilities enabled (see ptrace (2)).
Exect and execv may fail and set errno for any of the errors specified for the library function execve (2).
The behavior of execlp and 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 execlp and execvp ignored all errors except for the ones described above and ENOMEM and E2BIG, upon which they returned. They now return if any error other than the ones described above occurs.