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 for
detailed information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which is to
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, and, since these are
variadic functions, this pointer must be cast (char *) NULL.
The 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 function also specifies 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, the
default path ``:/bin:/usr/bin'' is used. In addition, certain errors are
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 the global
variable 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
On some other systems the default path (used when the environment does not
contain the variable PATH) has the current working directory listed
after /bin and /usr/bin, as an anti-Trojan-horse measure. Linux
uses here the traditional "current directory first" default path.
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. BSD (and possibly
other systems) do an automatic sleep and retry if ETXTBSY is encountered.
Linux treats it as a hard error and returns immediately.
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.