The
exec family of functions replaces the current process image with a new process image. The functions described in this manual page are front-ends for the function
execve(2). (See the manual page for
execve(2) for detailed information about the replacement of the current process. The
script(7) manual page provides detailed information about the execution of interpreter scripts.)
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 being 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 the
PATH variable. If this variable isn't specified,
_PATH_DEFPATH from
<paths.h> is used instead, its value being:
/usr/bin:/bin:/usr/pkg/bin:/usr/local/bin. In addition, certain errors are treated specially.
If permission is denied for a file (the attempted
execve(2) returned
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
EACCES.
If the header of a file isn't recognized (the attempted
execve(2) 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(2) 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)).