exec.2 (2010 09)

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exec(2) exec(2)

NAME

exec: execl(), execle(), execlp(), execv(), execve(), execvp() - execute a ﬁle

SYNOPSIS

#include <unistd.h>

extern char **environ;

int execl(const char *path,

const char *arg0, ...

* [const char *arg1, ..., const char *argn,

]

(char *)0);

int execle(const char *path,

const char *arg0, ...

* [const char *arg1, ..., const char *argn,

]

(char *)0,

char * const envp[]);

int execlp(const char *file,

const char *arg0, ...

* [const char *arg1, ..., const char *argn,]

(char *)0);

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

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

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

Remarks

The ANSI C ", ..." construct denotes a variable length argument list whose optional and required

members are given in the associated comment (/* */).

DESCRIPTION

The

exec*() system calls, in all their forms, load a program from an ordinary executable ﬁle into the

current process, replacing the current program. The path or ﬁle argument refers to either an executable

object ﬁle or a ﬁle of data for an interpreter. In the latter case, the ﬁle of data is also called a script ﬁle.

If the calling process is multi-threaded, a call to any of the exec functions will cause all threads and light

weight processes in the calling process to be terminated and the new executable image to be loaded and

executed. No thread speciﬁc data destructor functions are called. If the

exec() function fails and

returns to the caller, threads and light weight processes (LWPs) in the calling process will not be ter-

minated.

An executable object ﬁle consists of a header (see a.out (4)), text segment, and data segment. The data

segment contains an initialized portion and an uninitialized portion (bss). For

execlp() and

execvp() the POSIX shell (see sh-posix (1)) can be loaded to interpret a script instead. A successful call

to exec*() does not return because the new program overwrites the calling program.

When a C program is executed, it is called as follows:

main (int argc, char **argv, char **envp)

where argc is the argument count and argv is the address of an array of character pointers to the argu-

ments themselves. As indicated, argc usually has a value of at least one, and the ﬁrst member of the

array points to a string containing the name of the ﬁle. Exit conditions from main are discussed in

exit (2).

path points to a path name that identiﬁes the executable ﬁle containing the new program.

ﬁle (in

execlp() or execvp()) points to a ﬁle name identifying the executable ﬁle containing the new

program. The path preﬁx for this ﬁle is obtained by searching the directories passed in the environment

variable PATH (see environ (5)). The environment is supplied by the shell (see sh(1)). If ﬁle does not have

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
exec(2) exec(2) NAME exec: execl(), execle(), execlp(), execv(), execve(), execvp() - execute a file SYNOPSIS #include extern char **environ; int execl(const char *path, const char *arg0, ... /* * [const char *arg1, ... , const char *argn,] */ (char *)0); int execle(const char *path, const char *arg0, ... /* * [const char *arg1, ... , const char *argn,] */ (char *)0, char * const envp[]); A int execlp(const char *file, const char *arg0, ... /* * [const char *arg1, ...
PAGE 2
exec(2) exec(2) an executable magic number (see magic (4)), it is passed to the POSIX shell as a shell script. arg0 , ..., argn are one or more pointers to null-terminated character strings. These strings constitute the argument list available to the new program. By convention, at least arg0 must be present and point to a string identical to path or to path ’s last component. argv is an array of character pointers to null-terminated strings.
PAGE 3
exec(2) exec(2) • • • • • • • semadj values (see semop (2)) session membership signal mask (see sigprocmask (2)) supplementary group IDs time left until an alarm clock signal (see alarm (2)) trace flag (see ttrace (2) request TT_PROC_SETTRC) tms_utime, tms_stime, tms_cutime, and tms_cstime (see times (2)) For a script file, the initial line of a script file must begin with #! as the first two bytes, followed by zero or more spaces, followed by interpreter or interpreter argument , as in: #! interpreter
PAGE 4
exec(2) exec(2) [EINVAL] argv points to NULL and null pointer dereferencing is allowed. In this case, NULL is a valid address, but is considered an invalid argument. [ELOOP] Too many symbolic links were encountered in translating the path name. [ENAMETOOLONG] The executable file’s path name or the interpreter’s path name exceeds PATH_MAX bytes, or the length of a component of the path name exceeds NAME_MAX bytes while _POSIX_NO_TRUNC is in effect. [ENOENT] path points to an empty string.