EXEC(3) Linux Programmer's Manual EXEC(3)
NAME
 execl, execlp, execle, execv, execvp, execvpe - execute a file
SYNOPSIS
 #include <unistd.h>
 extern char **environ;
 int execl(const char *pathname, const char *arg, ...
 /* (char *) NULL */);
 int execlp(const char *file, const char *arg, ...
 /* (char *) NULL */);
 int execle(const char *pathname, const char *arg, ...
 /*, (char *) NULL, char *const envp[] */);
 int execv(const char *pathname, char *const argv[]);
 int execvp(const char *file, char *const argv[]);
 int execvpe(const char *file, char *const argv[],
 char *const envp[]);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
 execvpe(): _GNU_SOURCE
DESCRIPTION
 The exec() family of functions replaces the current process image with
 a new process image. The functions described in this manual page are
 layered on top of execve(2). (See the manual page for execve(2) for
 further details about the replacement of the current process image.)
 The initial argument for these functions is the name of a file that is
 to be executed.
 The functions can be grouped based on the letters following the "exec"
 prefix.
 l - execl(), execlp(), execle()
 The const char *arg and subsequent ellipses 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 filename associated with the file being executed. The
 list of arguments must be terminated by a null pointer, and, since
 these are variadic functions, this pointer must be cast (char *) NULL.
 By contrast with the 'l' functions, the 'v' functions (below) specify
 the command-line arguments of the executed program as a vector.
 v - execv(), execvp(), execvpe()
 The char *const argv[] argument is an array of pointers to null-termi-
 nated 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.
 e - execle(), execvpe()
 The environment of the caller is specified via the argument envp. The
 envp argument is an array of pointers to null-terminated strings and
 must be terminated by a null pointer.
 All other exec() functions (which do not include 'e' in the suffix)
 take the environment for the new process image from the external vari-
 able environ in the calling process.
 p - execlp(), execvp(), execvpe()
 These functions duplicate the actions of the shell in searching for an
 executable file if the specified filename does not contain a slash (/)
 character. The file is sought in the colon-separated list of directory
 pathnames specified in the PATH environment variable. If this variable
 isn't defined, the path list defaults to a list that includes the di-
 rectories returned by confstr(_CS_PATH) (which typically returns the
 value "/bin:/usr/bin") and possibly also the current working directory;
 see NOTES for further details.
 If the specified filename includes a slash character, then PATH is ig-
 nored, and the file at the specified pathname is executed.
 In addition, certain errors are treated specially.
 If permission is denied for a file (the attempted execve(2) failed with
 the error EACCES), these functions will continue searching the rest of
 the search path. If no other file is found, however, they will return
 with errno set to EACCES.
 If the header of a file isn't recognized (the attempted execve(2)
 failed with the error ENOEXEC), these functions will execute the shell
 (/bin/sh) with the path of the file as its first argument. (If this
 attempt fails, no further searching is done.)
 All other exec() functions (which do not include 'p' in the suffix)
 take as their first argument a (relative or absolute) pathname that
 identifies the program to be executed.
RETURN VALUE
 The exec() functions return only if an error has occurred. The return
 value is -1, and errno is set to indicate the error.
ERRORS
 All of these functions may fail and set errno for any of the errors
 specified for execve(2).
VERSIONS
 The execvpe() function first appeared in glibc 2.11.
ATTRIBUTES
 For an explanation of the terms used in this section, see at-
 tributes(7).
 +------------------------------+---------------+-------------+
 |Interface | Attribute | Value |
 +------------------------------+---------------+-------------+
 |execl(), execle(), execv() | Thread safety | MT-Safe |
 +------------------------------+---------------+-------------+
 |execlp(), execvp(), execvpe() | Thread safety | MT-Safe env |
 +------------------------------+---------------+-------------+
CONFORMING TO
 POSIX.1-2001, POSIX.1-2008.
 The execvpe() function is a GNU extension.
NOTES
 The default search path (used when the environment does not contain the
 variable PATH) shows some variation across systems. It generally in-
 cludes /bin and /usr/bin (in that order) and may also include the cur-
 rent working directory. On some other systems, the current working is
 included after /bin and /usr/bin, as an anti-Trojan-horse measure. The
 glibc implementation long followed the traditional default where the
 current working directory is included at the start of the search path.
 However, some code refactoring during the development of glibc 2.24
 caused the current working directory to be dropped altogether from the
 default search path. This accidental behavior change is considered
 mildly beneficial, and won't be reverted.
 The behavior of execlp() and execvp() when errors occur while attempt-
 ing to execute the file is historic practice, but has not traditionally
 been documented and is not specified by the POSIX standard. BSD (and
 possibly other systems) do an automatic sleep and retry if ETXTBSY is
 encountered. Linux treats it as a hard error and returns immediately.
 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 de-
 scribed above occurs.
BUGS
 Before glibc 2.24, execl() and execle() employed realloc(3) internally
 and were consequently not async-signal-safe, in violation of the re-
 quirements of POSIX.1. This was fixed in glibc 2.24.
 Architecture-specific details
 On sparc and sparc64, execv() is provided as a system call by the ker-
 nel (with the prototype shown above) for compatibility with SunOS.
 This function is not employed by the execv() wrapper function on those
 architectures.
SEE ALSO
 sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), sys-
 tem(3), environ(7)
COLOPHON
 This page is part of release 5.10 of the Linux man-pages project. A
 description of the project, information about reporting bugs, and the
 latest version of this page, can be found at
 https://www.kernel.org/doc/man-pages/.
GNU 2019年08月02日 EXEC(3)