- NetBSD Manual Pages
EXEC(3) NetBSD Library Functions Manual EXEC(3)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
execl, execlp, execle, exect, execv, execvp -- execute a file
Standard C Library (libc, -lc)
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 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 point-
ers 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 speci-
fied 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)).
If any of the exec functions returns, an error will have occurred. The
return value is -1, and the global variable errno will be set to indicate
/bin/sh The shell.
execl(), execle(), execlp() and execvp() may fail and set errno for any
of the errors specified for the library functions execve(2) and
exect() and execv() may fail and set errno for any of the errors speci-
fied for the library function execve(2).
sh(1), execve(2), fork(2), ptrace(2), environ(7), script(7)
Historically, the default path for the execlp() and execvp() functions
was ``:/bin:/usr/bin''. This was changed to improve security and behav-
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
execl(), execv(), execle(), execlp() and execvp() conform to ISO/IEC
NetBSD 5.1 May 6, 2005 NetBSD 5.1