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EXEC(3)                FreeBSD Library Functions Manual                EXEC(3)

     execl, execlp, execle, exect, execv, execvp - execute a file

     Standard C Library (libc, -lc)

     #include <unistd.h>

     extern char **environ;

     execl(const char *path, const char *arg, ...);

     execlp(const char *file, const char *arg, ...);

     execle(const char *path, const char *arg, ...);

     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

     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 ``PATH'' variable.  If this variable
     isn't specified, the default path is set according to the _PATH_DEFPATH
     definition in <paths.h>, which is set to ``/usr/bin:/bin''.  In addition,
     certain errors are treated specially.

     If an error is ambiguous (for simplicity, we shall consider all errors
     except ENOEXEC as being ambiguous here, although only the critical error
     EACCES is really ambiguous), then these functions will act as if they
     stat the file to determine whether the file exists and has suitable
     execute permissions.  If it does, they will return immediately with the
     global variable errno restored to the value set by execve().  Otherwise,
     the search will be continued.  If the search completes without performing
     a successful execve() or terminating due to an error, these functions
     will return with the global variable errno set to EACCES or ENOENT
     according to whether at least one file with suitable execute permissions
     was found.

     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.)

     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
     the error.

     /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
     specified for the library function execve(2).

     sh(1), execve(2), fork(2), ktrace(2), ptrace(2), environ(7)

     Historically, the default path for the execlp() and execvp() functions
     was ``:/bin:/usr/bin''.  This was changed to place the current directory
     last to enhance system security.

     The behavior of execlp() and execvp() when errors occur while attempting
     to execute the file is not quite historic practice, and 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 ETXTBSY, upon which they retried
     after sleeping for several seconds, and ENOMEM and E2BIG, upon which they
     returned.  They now return for ETXTBSY, and determine existence and
     executability more carefully.  In particular, EACCES for inaccessible
     directories in the path prefix is no longer confused with EACCES for
     files with unsuitable execute permissions.  In 4.4BSD, they returned upon
     all errors except EACCES, ENOENT, ENOEXEC and ETXTBSY.  This was inferior
     to the traditional error handling, since it breaks the ignoring of errors
     for path prefixes and only improves the handling of the unusual ambiguous
     error EFAULT and the unusual error EIO.  The behaviour was changed to
     match the behaviour of sh(1).

     Execl(), execv(), execle(), execlp() and execvp() conform to IEEE Std
     1003.1-1988 (``POSIX.1'').

FreeBSD 11.0-PRERELEASE        January 24, 1994        FreeBSD 11.0-PRERELEASE


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