Unix/Linux Go Back    


NetBSD 6.1.5 - man page for exec (netbsd section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


EXEC(3) 			   BSD Library Functions Manual 			  EXEC(3)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     extern char **environ;

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

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

     int
     execle(const char *path, const char *arg, ..., char *const envp[]);

     int
     exect(const char *path, char *const argv[], char *const envp[]);

     int
     execv(const char *path, char *const argv[]);

     int
     execvp(const char *file, char *const argv[]);

DESCRIPTION
     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 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-
     cially.

     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
     ptrace(2)).

RETURN VALUES
     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.

FILES
     /bin/sh  The shell.

ERRORS
     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
     function execve(2).

SEE ALSO
     sh(1), execve(2), fork(2), ptrace(2), environ(7), script(7)

COMPATIBILITY
     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
     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 above occurs.

STANDARDS
     execl(), execv(), execle(), execlp() and execvp() conform to ISO/IEC 9945-1:1990
     (``POSIX.1'').

BSD					   May 6, 2005					      BSD
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 05:11 AM.