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Manuál Linux
[Linux manuál]

exec: spouštět příkazy a otevírat, zavírat nebo kopírovat popisovače souborů

Originální popis anglicky: exec - execute commands and open, close, or copy file descriptors

Návod, kniha: POSIX Programmer's Manual

STRUČNĚ

exec [command [argument ...]]

POPIS / INSTRUKCE

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.

OPTIONS

None.

OPERANDS

See the DESCRIPTION.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

None.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

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 Consequences of Shell Errors ), the shell shall exit with a value in the range 1-125. Otherwise, exec shall return a zero exit status.

CONSEQUENCES OF ERRORS

Default.
The following sections are informative.

APPLICATION USAGE

None.

PŘÍKLADY POUŽITÍ

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

RATIONALE

Most historical implementations were not conformant in that:
 
foo=bar exec cmd
did not pass foo to cmd.

FUTURE DIRECTIONS

None.

SOUVISEJÍCÍ

Special Built-In Utilities Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
2003 IEEE/The Open Group
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