1EXEC(P)                    POSIX Programmer's Manual                   EXEC(P)
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NAME

6       exec - execute commands and open, close, or copy file descriptors
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SYNOPSIS

9       exec [command [argument ...]]
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DESCRIPTION

12       The  exec  utility  shall  open, close, and/or copy file descriptors as
13       specified by any redirections as part of the command.
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15       If exec is  specified  without  command  or  arguments,  and  any  file
16       descriptors  with numbers greater than 2 are opened with associated re‐
17       direction statements, it is unspecified whether those file  descriptors
18       remain  open  when the shell invokes another utility. Scripts concerned
19       that child shells could misuse open file descriptors can  always  close
20       them explicitly, as shown in one of the following examples.
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22       If exec is specified with command, it shall replace the shell with com‐
23       mand without creating a new process.  If arguments are specified,  they
24       shall  be  arguments to command.  Redirection affects the current shell
25       execution environment.
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OPTIONS

28       None.
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OPERANDS

31       See the DESCRIPTION.
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STDIN

34       Not used.
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INPUT FILES

37       None.
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ENVIRONMENT VARIABLES

40       None.
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ASYNCHRONOUS EVENTS

43       Default.
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STDOUT

46       Not used.
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STDERR

49       The standard error shall be used only for diagnostic messages.
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OUTPUT FILES

52       None.
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EXTENDED DESCRIPTION

55       None.
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EXIT STATUS

58       If command is specified, exec shall not return to  the  shell;  rather,
59       the  exit status of the process shall be the exit status of the program
60       implementing command, which overlaid  the  shell.  If  command  is  not
61       found, the exit status shall be 127. If command is found, but it is not
62       an executable utility, the exit status shall be 126. If  a  redirection
63       error  occurs (see Consequences of Shell Errors ), the shell shall exit
64       with a value in the range 1-125. Otherwise, exec shall  return  a  zero
65       exit status.
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CONSEQUENCES OF ERRORS

68       Default.
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70       The following sections are informative.
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APPLICATION USAGE

73       None.
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EXAMPLES

76       Open readfile as file descriptor 3 for reading:
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79              exec 3< readfile
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81       Open writefile as file descriptor 4 for writing:
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84              exec 4> writefile
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86       Make file descriptor 5 a copy of file descriptor 0:
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89              exec 5<&0
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91       Close file descriptor 3:
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94              exec 3<&-
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96       Cat  the  file maggie by replacing the current shell with the cat util‐
97       ity:
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100              exec cat maggie
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RATIONALE

103       Most historical implementations were not conformant in that:
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106              foo=bar exec cmd
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108       did not pass foo to cmd.
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FUTURE DIRECTIONS

111       None.
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SEE ALSO

114       Special Built-In Utilities
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COPYRIGHT

117       Portions of this text are reprinted and reproduced in  electronic  form
118       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
119       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
120       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
121       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
122       event of any discrepancy between this version and the original IEEE and
123       The Open Group Standard, the original IEEE and The Open Group  Standard
124       is  the  referee document. The original Standard can be obtained online
125       at http://www.opengroup.org/unix/online.html .
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129IEEE/The Open Group                  2003                              EXEC(P)