EXEC(3) BSD Library Functions Manual EXEC(3)
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
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 exe-
cuted 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 spe-
If permission is denied for a file (the attempted execve(2) returned EACCES), these func-
tions will continue searching the rest of the search path. If no other file is found, how-
ever, 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
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 the error.
/bin/sh The shell.
execl(), execle(), execlp() and execvp() may fail and set errno for any of the errors speci-
fied for the library functions execve(2) and malloc(3).
exect() and execv() may fail and set errno for any of the errors specified for the library
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 behaviour.
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
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.
execl(), execv(), execle(), execlp() and execvp() conform to ISO/IEC 9945-1:1990
BSD May 6, 2005 BSD