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(5) 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(5) for descriptions of the following attributes:


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

SEE ALSO


open(2), attributes(5), fsattr(5)

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)