Retrv retrieves a specified, previously saved version of a file
from the version object base. The version archive is expected to
reside in the AtFS subdirectory. A selected version will by default be
retrieved into a file in the directory where it was originally saved.
If just a copy of a file version shall be retrieved, this behavior can
be overridden with the -dest option. If a busy version is created
with the -lock option, it must be created in the directory from
where it was saved. This is necessary to maintain the spatial relationship
between the busy version and the corresponding history archive, residing in
the AtFS subdirectory.
Retrieve tries to be careful if an attempt is made to overwrite an
existing busy-version: unless -f (-force)
is specified, retrv will ask the caller for permission.
If no busy version exists, one is created with the same modes as the
formerly saved version. If a busy version exists, its modes are preserved.
If the program is invoked as vcat, the specified version(s)
will be printed on standard output. No status change of the
object base will occur in this case.
vcat behaves similar to the cat(1) command: if just a filename
is given, vcat displays the most recent status of the referenced
object. If a busy version does exist it will be selected as most recent
status. If no busy version exists, vcat displays the most recently
saved version.
ATTRIBUTE CITATIONS
It is possible to cite any of a file-version's attributes within the
the body of the version. This can be done by using attribute citation
expressions. These expressions have the form "$__attributename$".
Version attributes that are cited within the text of a stored revision
are expanded by default. In this case, the citation expression will be
substituted by the cited attribute's value. For a list of predefined
attribute names, check the vadm(1) manual page.
There are three basic kinds of attribute values: genuine values,
reference values, and execution values. Genuine
values are simply strings that are assigned to an attribute.
Reference values are pointers to files or AtFS-versions whose
contents will be substituted in place of an attribute-citation.
Reference values are strings that begin with a circumflex-character,
typically followed by pathname, e.g.
^/usr/local/lib/std-header[2.4]. Execution values are
names of executable programs, whose standard output is substituted in
place of an attribute-citation. Execution values are strings that
begin with an exclamation-mark character, typically followed by the
name of the program, e.g. !/bin/date. Execution values can be
used to generate highly dynamic attributes or a primitive form of
event-triggers.
When expanding an attribute
citation, retrv first looks for an attribute of the mentioned name
within the version's set of associated attributes. If no attribute of that
name can be found, the environment is searched for a variable of that
name. In case the cited attribute exists and has a value, the value is
itself searched for attribute-citations that are expanded recursively.
If neither an attribute nor an environment variable of the cited name can be
found, no substitution takes place and the expression will be left
unchanged. The same is true if a referenced object of a reference
value does not exist, or an execution value happens to not be executable.
Attribute citation expressions are also left unchanged
if a revision is retrieved with the -lock option.
Expansion of attribute citation within documents can be controlled
by the pseudo-attribute citations "$__xpoff$" and "$__xpon$".
OPTIONS
For version selection, any version binding option, as described
on the vbind(1) manual page, may be given, or a version bind
directive may be given in brackets added to the file name.
Additional options are:
"-?,
print brief instructions about using this program.
"-c,
Do not check for equality. Usually, retrv checks whether an existing
destination file is identical to the version to be retrieved and
suppresses copying in this case. This behaviour is mainly for
efficiency reasons and may be disabled by the -c switch.
-dest path
retrieve the specified version from the object base and install
a copy it in the directory denoted by path. As this
directory may be a long way apart from the directory containing
the AtFS archives, this copy of the retrieved version is separated
from its history and subsequently unrelated to the object
history it came from. Proper object histories require a constant
spatial relationship of any busy versions and the corresponding
archives. This relationship requires the archives to reside
in a subdirectory named AtFS.
-fix
attempt to reserve the privilege to add a new version to an old
generation
(insert a new minor revision into an old major revision) within the object
history. If successful, the user who issued the command holds a
generation lock. There can be only one lock per
generation, preventing simultaneous updates of the generation. The
generation lock is, by convention, a revision lock (see vadm
-lock) attached to the version with the highest version number
within a generation.
The -fix switch is intended to support concurrency of the main
development process and maintenance activities (such as bug fixing) for older
releases. When a version is retrieved with the purpose to fix it, it
is called the fixpoint version. The fixpoint version accumulates
all fixes applied to a baseline version within a generation. One
important advantage of this policy is the elimination of the need to
create a branch for each fix that must later be merged with the
``mainline'' version, containing previous fixes. So, if retrv is
invoked with ``-fix'' it will restore the fixpoint version (the most
recent minor revision within the implied generation) rather than the
explicitly referenced version. However,
retrv issues a warning, if the baseline- and the fixpoint
version are not identical.
To insert a fix into an old generation, use the -fix
option of the save command.
When setting a lock on a generation, the requesting user
is prompted for an optional description of the planned changes.
The -fix switch is incompatible with -lock.
"-f,
force the reinstallation of the specified version as busy version without
asking the user, even if a writable (possibly unsaved) busy version
exists.
"-i message"
set message as intent text describing
the changes that are intended to be applied to a busy version
that is installed by retrv. When message
starts with an at sign (@), it is interpreted as filename and the text
contained in the file is takes as intent text. If message is
``-'', the change intent is read from standard input. The
latter case is identical to specifying the command line switch
-stdin. This option requires the -lock switch to be set
in order to be effective.
"-l,
attempt to reserve the privilege to add a new version to the main
development line of an object
history, thus preventing multiple programmers working upon the same
object base from interfering with each other by saving concurrent updates.
When setting a new lock on an object history, prompt the requesting user
for an optional description of the planned changes.
The -lock switch is incompatible with -fix.
"-q,
quiet operation. No messages are printed on standard output.
If a current busy version exists, it will not be overwritten by
the specified version unless -f is set. This option is useful for
batch operation.
-stdin
force retrv to read the message describing the change intent
from stdin rather than fork an editor.
-version
print version identification for this program.
-xpoff
Do not expand attribute citations in the restored file.
FILES
All revisions of documents are retrieved from archive files located
in the subdirectory AtFS.
