Manpage of EXEC

EXEC

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

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

SYNOPSIS

#include <unistd.h>

extern char **environ;

int execl(const char *path, const char *arg, ...
/* (char *) NULL */);
int execlp(const char *file, const char *arg, ...
/* (char *) NULL */);
int execle(const char *path, const char *arg, ...
/*, (char *) NULL, 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[]);

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 front-ends for 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 const char *argand 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 filename associated with the file being executed. The list of arguments mustbe terminated by a null pointer, and, since these are variadic functions, this pointer must be cast (char *) NULL.

The execv(), execvp(), and execvpe() 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 filename associated with the file being executed. The array of pointers mustbe terminated by a null pointer.

The execle() and execvpe() functions allow the caller to specify the environment of the executed program via the argument envp. The envpargument is an array of pointers to null-terminated strings and mustbe terminated by a null pointer. The other functions take the environment for the new process image from the external variable environin the calling process.  

Special semantics for execlp() and execvp()

The execlp(), execvp(), and execvpe() 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 PATHenvironment variable. If this variable isn't defined, the path list defaults to the current directory followed by the list of directories returned by confstr(_CS_PATH). (This confstr(3) call typically returns the value "/bin:/usr/bin".)

If the specified filename includes a slash character, then PATHis ignored, 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 errnoset 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.)  

RETURN VALUE

The exec() functions return only if an error has occurred. The return value is -1, and errnois set to indicate the error.  

ERRORS

All of these functions may fail and set errnofor 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 attributes(7).
InterfaceAttributeValue
execl(), execle(), execv() Thread safetyMT-Safe
execlp(), execvp(), execvpe() Thread safetyMT-Safe env
 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

The execvpe() function is a GNU extension.  

NOTES

On some other systems, the default path (used when the environment does not contain the variable PATH) has the current working directory listed after /binand /usr/bin, as an anti-Trojan-horse measure. Linux uses here the traditional "current directory first" default path.

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. BSD (and possibly other systems) do an automatic sleep and retry if ETXTBSYis 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 ENOMEMand E2BIG, upon which they returned. They now return if any error other than the ones described above occurs.  

SEE ALSO

sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), system(3), environ(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
Special semantics for execlp() and execvp()
RETURN VALUE
ERRORS
VERSIONS
ATTRIBUTES
CONFORMING TO
NOTES
SEE ALSO

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Time: 22:27:51 GMT, June 20, 2016