RUNAT(1) User Commands RUNAT(1)

NAME

runat - execute command in extended attribute name space

SYNOPSIS

/usr/bin/runat file [command]

DESCRIPTION

The runat utility is used to execute shell commands in a file's
hidden attribute directory. Effectively, this utility changes the
current working directory to be the hidden attribute directory
associated with the file argument and then executes the specified
command in the bourne shell (/bin/sh). If no command argument is
provided, an interactive shell is spawned. The environment variable
$SHELL defines the shell to be spawned. If this variable is
undefined, the default shell, /bin/sh, is used.


The file argument can be any file, including a directory, that can
support extended attributes. It is not necessary that this file have
any attributes, or be prepared in any way, before invoking the runat
command.

OPERANDS

The following operands are supported:

file
Any file, including a directory, that can support
extended attributes.


command
The command to be executed in an attribute directory.

ERRORS

A non-zero exit status will be returned if runat cannot access the
file argument, or the file argument does not support extended
attributes.

USAGE

See fsattr(7) for a detailed description of extended file attributes.


The process context created by the runat command has its current
working directory set to the hidden directory containing the file's
extended attributes. The parent of this directory (the ".." entry)
always refers to the file provided on the command line. As such, it
may not be a directory. Therefore, commands (such as pwd) that
depend upon the parent entry being well-formed (that is, referring to
a directory) may fail.


In the absence of the command argument, runat will spawn a new
interactive shell with its current working directory set to be the
provided file's hidden attribute directory. Notice that some shells
(such as zsh and tcsh) are not well behaved when the directory parent
is not a directory, as described above. These shells should not be
used with runat.

EXAMPLES

Example 1: Using runat to list extended attributes on a file

example% runat file.1 ls -l
example% runat file.1 ls

Example 2: Creating extended attributes

example% runat file.2 cp /tmp/attrdata attr.1
example% runat file.2 cat /tmp/attrdata > attr.1

Example 3: Copying an attribute from one file to another

example% runat file.2 cat attr.1 | runat file.1 "cat > attr.1"

Example 4: Using runat to spawn an interactive shell

example% runat file.3 /bin/sh


This spawns a new shell in the attribute directory for file.3. Notice
that the shell will not be able to determine what your current
directory is. To leave the attribute directory, either exit the
spawned shell or change directory (cd) using an absolute path.


Recommended methods for performing basic attribute operations:


display
runat file ls [options]


read
runat file cat attribute


create/modify
runat file cp absolute-file-path attribute


delete
runat file rm attribute


permission changes

runat file chmod mode attribute
runat file chgrp group attribute
runat file chown owner attribute


interactive shell

runat file /bin/sh or set your $SHELL to /bin/sh and runat file


The above list includes commands that are known to work with runat.
While many other commands may work, there is no guarantee that any
beyond this list will work. Any command that relies on being able to
determine its current working directory is likely to fail. Examples
of such commands follow:

Example 5: Using man in an attribute directory

example% runat file.1 man runat
>getcwd: Not a directory

Example 6: Spawning a tcsh shell in an attribute directory

example% runat file.3 /usr/bin/tcsh
tcsh: Not a directory
tcsh: Trying to start from "/home/user"


A new tcsh shell has been spawned with the current working directory
set to the user's home directory.

Example 7: Spawning a zsh shell in an attribute directory

example% runat file.3 /usr/bin/zsh
example%


While the command appears to have worked, zsh has actually just
changed the current working directory to '/'. This can be seen by
using /bin/pwd:


example% /bin/pwd
/

ENVIRONMENT VARIABLES

SHELL
Specifies the command shell to be invoked by runat.

EXIT STATUS

The following exit values are returned:

125
The attribute directory of the file referenced by the file
argument cannot be accessed.


126
The exec of the provided command argument failed.


Otherwise, the exit status returned is the exit status of the shell
invoked to execute the provided command.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|CSI | Enabled |
+--------------------+-----------------+
|Interface Stability | Evolving |
+--------------------+-----------------+

SEE ALSO

open(2), attributes(7), fsattr(7)

NOTES

It is not always obvious why a command fails in runat when it is
unable to determine the current working directory. The errors
resulting can be confusing and ambiguous (see the tcsh and zsh
examples above).

June 22, 2001 RUNAT(1)