Проект OpenNet: MAN exec (1) Команды и прикладные программы пользовательского уровня (FreeBSD и Linux)

Интерактивная система просмотра системных руководств (man-ов)

exec (1)

>> exec (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )

exec (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )

exec (1) ( Linux man: Команды и прикладные программы пользовательского уровня )

exec (1) ( POSIX man: Команды и прикладные программы пользовательского уровня )

exec (2) ( Solaris man: Системные вызовы )

exec (3) ( FreeBSD man: Библиотечные вызовы )

exec (3) ( Русские man: Библиотечные вызовы )

exec (3) ( Linux man: Библиотечные вызовы )

exec (3) ( POSIX man: Библиотечные вызовы )

Ключ exec обнаружен в базе ключевых слов.

NAME

exec, eval, source - shell built-in functions to execute other commands

SYNOPSIS

sh

exec [argument]...

eval [argument]...

csh

exec command

eval argument...

source [-h] name

ksh

*exec [argument]...

*eval [argument]...

ksh93

+exec [-c] [-a name] [command [argument ... ]]

+eval [argument]...

DESCRIPTION

sh

The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments and appear and, if no other arguments are specified, cause the shell input/output to be modified.

The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.

csh

exec executes command in place of the current shell, which terminates.

eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as the result of command or variable substitution.

source reads commands from name. source commands can be nested, but if they are nested too deeply the shell can run out of file descriptors. An error in a sourced file at any level terminates all nested source commands.

-h

: Place commands from the file name on the history list without executing them.

ksh

With the exec built-in, if arg is specified, the command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments can appear and affect the current process. If no arguments are specified the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.

The arguments to eval are read as input to the shell and the resulting command(s) executed.

On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

1.: Variable assignment lists preceding the command remain in effect when the command completes.

2.: I/O redirections are processed after variable assignments.

3.: Errors cause a script that contains them to abort.

4.: Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

ksh93

exec is a special built-in command that can be used to manipulate file descriptors or to replace the current shell with a new command.

If command is specified, then the current shell process is replaced by command rather than running command and waiting for it to complete. There is no need to use exec to enhance performance since the shell implicitly uses the exec mechanism internally whenever possible.

If no operands are specified, exec can be used to open or close files, or to manipulate file descriptors from 0 to 9 in the current shell environment using the standard redirection mechanism available with all commands. The close-on-exec flags is set on file descriptor numbers greater than 2 that are opened this way so that they are closed when another program is invoked.

Because exec is a special command, any failure causes the script that invokes it to exit. This can be prevented by invoking exec from the command utility.

exec cannot be invoked from a restricted shell to create files or to open a file for writing or appending.

eval is a shell special built-in command that constructs a command by concatenating the arguments together, separating each with a space. The resulting string is taken as input to the shell and evaluated in the current environment. command words are expanded twice, once to construct argument, and again when the shell executes the constructed command. It is not an error if argument is not specified.

On this manual page, ksh93 commands that are preceded by one or two + symbols are special built-in commands and are treated specially in the following ways:

1.: Variable assignment lists preceding the command remain in effect when the command completes.

2.: I/O redirections are processed after variable assignments.

3.: Errors cause a script that contains them to abort.

4.: They are not valid function names.

5.: Words following a command preceded by ++ that are in the format of a variable assignment are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and field splitting and file name generation are not performed.