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EXEC(3) Linux Programmer's Manual EXEC(3)


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


     #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


     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 fur-
     ther 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 *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-termi-
     nated strings that represent the argument list available  to  the  exe-
     cuted  program.  The first argument, by convention, should point to the
     filename associated with the file being executed.  The  list  of  argu-
     ments  must be terminated by a null pointer, and, since these are vari-
     adic 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 must be 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 envp
     argument 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
     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 file-
     name does not contain a slash (/) character.  The file is sought in the
     colon-separated list of directory pathnames specified in the PATH envi-
     ronment  variable.   If  this  variable  isn't  defined,  the path list
     defaults to a list that includes  the  directories  returned  by  conf-
     str(_CS_PATH)  (which  typically returns the value "/bin:/usr/bin") and
     possibly also the current working  directory;  see  NOTES  for  further
     If  the  specified  filename  includes  a slash character, then PATH is
     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 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.)


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


     All  of  these  functions  may fail and set errno for any of the errors
     specified for execve(2).


     The execvpe() function first appeared in glibc 2.11.


     For  an  explanation  of  the  terms  used   in   this   section,   see
     allbox;  lbw29 lb lb l l l.  Interface Attribute Value T{ execl(), exe-
     cle(),  execv()  T}   Thread  safety  MT-Safe  T{  execlp(),  execvp(),
     execvpe() T}   Thread safety  MT-Safe env


     POSIX.1-2001, POSIX.1-2008.
     The execvpe() function is a GNU extension.


     The default search path (used when the environment does not contain the
     variable PATH) shows  some  variation  across  systems.   It  generally
     includes  /bin  and  /usr/bin  (in that order) and may also include the
     current 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
     described above occurs.


     Before  glibc 2.24, execl() and execle() employed realloc(3) internally
     and were  consequently  not  async-signal-safe,  in  violation  of  the
     requirements of POSIX.1.  This was fixed in glibc 2.24.


     sh(1),  execve(2),  execveat(2),  fork(2),  ptrace(2), fexecve(3), sys-
     tem(3), environ(7)


     This page is part of release 4.16 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

GNU 2017-09-15 EXEC(3)

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