execl(3) - NetBSD Manual Pages

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EXEC(3)                 NetBSD Library Functions Manual                EXEC(3)


NAME

     execl, execlp, execlpe, execle, exect, execv, execvp, execvpe -- 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
     execlpe(const char *path, const char *arg, ..., char *const envp[]);

     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[]);

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


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(),
     execlpe(), and execle() functions can be thought of as arg0, arg1, ...,
     argn.  Together they describe a list of one or more pointers to NUL-ter-
     minated 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(), execvp(), and execvpe() functions provide an array
     of pointers to NUL-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(), execlpe(), exect(), and execvpe() 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 NUL-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 cur-
     rent process.

     Some of these functions have special semantics.

     The functions execlp(), execlpe(), execvp(), and execvpe() will duplicate
     the actions of the shell in searching for an executable file if the spec-
     ified 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 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)).


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.


COMPATIBILITY

     Historically, the default path for the execlp() execlpe(), execvp(), and
     execvpe() functions was ``:/bin:/usr/bin''.  This was changed to improve
     security and behaviour.

     The behavior of execlp(), execlpe(), execvp(), and execvpe() 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 stan-
     dard.

     Traditionally, the functions execlp(), execlpe(), execvp(), and execvpe()
     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.


ERRORS

     execl(), execle(), execlp(), execlpe(), execvp(), and execvpe() may fail
     and set errno for any of the errors specified for the library functions
     execve(2) and malloc(3).

     exect() and execv() may fail and set errno for any of the errors speci-
     fied for the library function execve(2).


SEE ALSO

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


STANDARDS

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


HISTORY

     The exec() function appeared in Version 1 AT&T UNIX.  The execlpe() func-
     tion appeared first in QNX and the execvpe() function exists on both
     NetBSD and QNX.

NetBSD 9.3                     September 1, 2019                    NetBSD 9.3