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EXEC(1P) POSIX Programmer's Manual EXEC(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
exec — execute commands and open, close, or copy file descriptors
exec [command [argument...]]
The exec utility shall open, close, and/or copy file descriptors as
specified by any redirections as part of the command.
If exec is specified without command or arguments, and any file
descriptors with numbers greater than 2 are opened with associated
redirection statements, it is unspecified whether those file
descriptors remain open when the shell invokes another utility.
Scripts concerned that child shells could misuse open file
descriptors can always close them explicitly, as shown in one of the
following examples.
If exec is specified with command, it shall replace the shell with
command without creating a new process. If arguments are specified,
they shall be arguments to command. Redirection affects the current
shell execution environment.
None.
See the DESCRIPTION.
Not used.
None.
None.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
If command is specified, exec shall not return to the shell; rather,
the exit status of the process shall be the exit status of the
program implementing command, which overlaid the shell. If command is
not found, the exit status shall be 127. If command is found, but it
is not an executable utility, the exit status shall be 126. If a
redirection error occurs (see Section 2.8.1, Consequences of Shell
Errors), the shell shall exit with a value in the range 1−125.
Otherwise, exec shall return a zero exit status.
Default.
The following sections are informative.
None.
Open readfile as file descriptor 3 for reading:
exec 3< readfile
Open writefile as file descriptor 4 for writing:
exec 4> writefile
Make file descriptor 5 a copy of file descriptor 0:
exec 5<&0
Close file descriptor 3:
exec 3<&−
Cat the file maggie by replacing the current shell with the cat
utility:
exec cat maggie
Most historical implementations were not conformant in that:
foo=bar exec cmd
did not pass foo to cmd.
None.
Section 2.14, Special Built-In Utilities
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 EXEC(1P)
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