VCP::Filter::map(3)

NAME
VCP::Filter::map - rewrite name, branch_id or delete revisions

SYNOPSIS
  ## In a .vcp file:

    Map:
            name_glob_1<branch_1> name_out_1<branch_result_1>
            name_glob_2<branch_2> name_out_2<branch_result_2>
            # ... etc ...

  ## From the command line:
   vcp <source> map: name_glob_1<branch_1> name_out_1<branch_result_1> -- <dest>

  ## you may have one or more ( pattern match ) pairs on the command
  ## line, ending with --

  ## the <branch> part of the maps is optional.

DESCRIPTION
Maps source files, revisions, and branches to destination files and branches while copying a repository. This is done by rewriting the "name" and "branch_id" of revisions according to a list of rules.

  Rules
A rule is a pair of expressions specifying a pattern to match against each incoming revision's name and branch_id and a replacement expression specifying the revision's new name and branch_id.

The list of rules is evaluated top down; the first rule in the list that matches is used to generate the new name and branch_id. If no other rules match the implicit default rule is to copy files as is.

  Patterns and Replacement Expressions
Patterns and replacements are each are composed of two subexpressions, the "name_expr" and the "branch_id_expr" like so:

    name_expr<branch_id_expr>

The "<branch_id_expr>" (including angle brackets) is optional and may be forbidden by some sources or destinations that embed the concept of a branch in the name_expr. (See VCP::Dest::p4 for an example, though this may be changed in the future).

For now, the symbols "#" and "@" are reserved for future used in all expressions and must be escaped using "\", and various shell-like wildcards are implemented in pattern expressions.

Pattern Expressions
Both the "name_expr" and "branch_id_expr" specify patterns using shell regular expression syntax with the extension that parentheses are used to extract portions of the match in to numbered variables which may be used in the result construction, like Perl regular expressions:

   ?      Matches one character other than "/"
   *      Matches zero or more characters other than "/"
   ...    Matches zero or more characters, including "/"
   (foo)  Matches "foo" and stores it in the $1, $2, etc

Some example pattern "name_expr"s are:

   Pattern
   name_expr  Matches
   =========  =======
   foo        the top level file "foo"
   foo/bar    the file "foo/bar"
   ...        all files (like a missing name_expr)
   foo/...    all files under "foo/"
   .../bar    all files named "bar" anywhere
   */bar      all files named "bar" one dir down
   ....pm     all files ending in ".pm"
   ?.pm       all top level 4 char files ending in ".pm"
   \?.pm      the top level file "?.pm"
   (*)/...    all files in subdirs, puts the top level dirname in $1

Unix-style slashes are used, even on operating systems where that may not be the preferred local custom. A pattern consisting of the empty string is legal and matches everything (NOTE: currently there is no way to take advantage of this; quoting is not implemented in the forms parser yet. use "..." instead).

Relative paths are taken relative to the rev_root indicated in the source specification for pattern "name_expr"s (or in the destination specification for result "name_expr"s). For now, a relative path is a path that does not begin with the character "/", so be aware that the pattern "(/)" is relative. This is a limitation of the implementation and may change, until it does, don't rely on a leading "(" making a path relative and use multiple rules to match multiple absolute paths.

If no "name_expr" is provided, "..." is assumed and the pattern will match on all filenames.

Some example pattern "branch_id_expr"s are:

    Pattern
    branch_id_expr  Matches files on
    =============   ================
    <>              no branch label
    <...>           all branches (like a missing <branch_id_expr>)
    <foo>           branch "foo"
    <R...>          branches beginning with "R"
    <R(...)>        branches beginning with "R", the other chars in $1

If no "branch_id_expr" is provided, files on all branches are matched. "*" and "..." still match differently in pattern "branch_id_expr"s, as in <name_expr> patterns, but this is likely to make no difference, as I've not yet seen a branch label with a "/" in it. Still, it is wise to avoid "*" in "branch_id_expr" patterns.

Some example composite patterns are (any $ variables set are given in parenthesis):

    Pattern            Matches
    =======            =======
    foo<>              top level files named "foo" not on a branch
    (...)<>            all files not on a branch ($1)
    (...)/(...)<>      all files not on a branch ($1,$2)
    ...<R1>            all files on branch "R1"
    .../foo<R...>      all files "foo" on branches beginning with "R"
    (...)/foo<R(...)>  all files "foo" on branches beginning with "R" ($1, $2)

  Escaping
Null characters and newlines are forbidden in all expressions.

The characters "#", "@", "[", "]", "{", "}", ">", "<" and "$" must be escaped using a "\", as must any wildcard characters meant to be taken literally.

In result expressions, the wildcard characters "*", "?", the wildcard trigraph "..." and parentheses must each be escaped with single "\" as well.

No other characters are to be escaped.

  Case sensitivity
By default, all patterns are case sensitive. There is no way to override this at present; one will be added.

  Result Expressions
Result expressions look a lot like patthern expressions except that wildcards are not allowed and $1 and "${1}" style variable interpolation is.

To explore result expressions, let's look at converting set of example files between cvs and p4 repositories. The difficulty here is that cvs and p4 have differing branching implementations.

Let's assume our CVS repository has a module named "flibble" with a file named "foo/bar" in it. Here is a branch diagram, with the main development trunk shown down the left (1.1 through 1.6, etc) and a single branch, tagged in CVS with a branch tag of "beta_1", is shown forking off version 1.5:

     flibble/foo/bar:

         1.1
          |
         ...
          |
         1.5
          | \
          |  \ beta_1
          |   \
         1.6   \
          |    1.5.2.1
         ...    |
                |
               1.5.2.2
                |
               ...

    NOTE 1: You can use C<vcp> to extract graphical branch diagrams by
    installing AT&T's GraphViz package and the Perl CPAN module
    GraphViz.pm.  Then you can use a command like:

        $ vcp cvs:/var/cvsroot:flibble/foo/bar \
            branch_diagram:foo_bar.png

    to generate a .png file showing something like the above diagram.

On the other hand, p4 users typically branch files using directory names. Here's file "foo/bar" again, with the main trunk held in the main depot's //depot/main directory, again with a branch after the 5th version of the file, but this time, the branch is represented by taking a copy

    //depot/main/foo/bar

         #1
          |
         ...
          |
         #5
          |\
          | \ //depot/beta_1/foo/bar
          |  \
         #6   \
          |   #1
         ...   |
               |
              #2
               |
              ...

    NOTE 2: the p4 command allows users to branch in very crafty and
    creative ways; it does not enforce the semantic of 1 branch per
    directory, and this gives p4 users a lot of power and flexibility.
    It also means that you might need some pretty crafty and creative
    branch maps when converting from p4 to other repositories.

    NOTE 3: that branch looks like a copy, but is actually just a
    metadata entry in the perforce repository, so it's very low
    overhead in terms of server effort and disk space, usually
    even more so than CVS branches.

    NOTE 4: Using GraphViz (as described in NOTE 1 above), you can
    build a diagram like this using vcp:

        $ vcp p4:perforce.our.com:1666://depot/flibble/foo/bar \
            branch_diagram:foo_bar.png

A user may or may not choose to label a branch in p4 with something called a "branch specification" (see "p4 help branch" for details). For this discussion, we'll assume they didn't.

First, let's look at cvs -> p4 conversion. To do this, we need to match the branch tags in the CVS repository and use them to map branched files in to a p4 subdirectory. Here's .vcp file for this:

   ## cvs2p4.vcp

   Source:
   # get all files in the flibble module from cvs
       cvs:/var/cvsroot:flibble/...

   Destination:
   # Put the files in the flibble directory in the main depot of p4
       p4:perforce.our.com:1666://depot/flibble/...

   Map:
   #   Pattern       Result
   #   ============  =======
       (...)<>       main/$1   # main trunk => //depot/flibble/main/...
       (...)<(...)>  $2/$1     # branches   => //depot/flibble/$branch/...

The "Source:" and "Destination:" fields are just pieces of a normal "vcp" command line moved in to "cvs2p4.vcp". The "Map:" field is a list of rules composed of pattern, result expression pairs.

In this example, all of the map expressions are relative paths. The patterns are relative to the "Source:" cvs repositories' ""flibble"" module. The results are relative to the "Destination:" p4 repositories' ""//depot/flibble/"" directory.

The first rule maps all files that have no branch tag in to the p4 directory "//depot/flibble/main/". The "(...)<>" pattern has two parts: a "name" part and a "branch_id" part. The "name" part, "(...)", matches all path names and copies them to the $1 variable. The "branch_id" part, " <" >, matches empty / missing "branch_id"s ("vcp"'s name for the CVS branch tag associated with a file on a branch). The " main/$1 " result retrieves the "name" part stored in $1 and prefixes it with ""main/"" to build the final "name" value.

The second rule maps all files on branches to an appropriately named subdirectory in the p4 destination. The pattern is a lot like the first rule's, but has a "branch_id" part that matches all "branch_id"s and copies them in to $2. The rule merely uses this "branch_id" from $2 instead of the hardcoded ""main/"" string to place the branches in appropriate subdirectories.

Here's how our flibble/foo/bar file version fare when passed through this mapping:

    CVS flibble/...              p4 //depot/flibble/...
    ========================     ======================

    foo/bar#1.1                  main/foo/bar#1
    foo/bar#1.2                  main/foo/bar#2
    ...                          ...
    foo/bar#1.5.2.1              beta_1/foo/bar#1
    foo/bar#1.5.2.2              beta_1/foo/bar#2
    ...                          ...

It's up to you to be sure there are no branches tagged ""main"" in the CVS repository. Also, no branch specification will be created in the target p4 repository (this is a limitation that should be fixed).

  Result Actions: <<delete>> and <<keep>>
The result expression "<<delete>>" indicates to delete the revision, while the result expression "<<keep>>" indicates to pass it through unchanged:

    Map:
    #   Pattern            Result
    #   =================  ==========
        old_stuff/...      <<delete>>  # Delete all files in /old
        old_stuff/.../*.c  <<keep>>    # except these

<<delete>> and <<keep>> may not appear in results; they are standalone tokens.

  The default rule
There is a default rule

    ...  <<keep>>  ## Default rule: passes everything through as-is

that is evaluated after all the other rules. Thus, if no other rule matches a revision, it is passed through unchanged.

  Command Line Parsing
For large maps or repeated use, the map is best specified in a .vcp file. For quick one-offs or scripted situations, however, the map: scheme may be used on the command line. In this case, each parameter is a "word" (separated by whitespace) and every pair of words is a ( pattern, result ) pair.

Because vcp command line parsing is performed incrementally and the next filter or destination specifications can look exactly like a pattern or result, the special token "--" is used to terminate the list of patterns provided on the command line. This may also be the last word in the "Map:" section of a .vcp file, but that is superfluous. It is an error to use "--" before the last word in a .vcp file.

LIMITATIONS
There is no way (yet) of telling the mapper to continue processing the rules list. We could implement labels like "<label>" to be allowed before pattern expressions (but not between pattern and result), and we could then impelement "<goto label>". And a "<next>" could be used to fall through to the next label. All of which is wonderful, but I want to gain some real world experience with the current system and find a use case for gotos and fallthroughs before I implement them. This comment is here to solicit feedback :).

AUTHOR
Barrie Slaymaker <barries@slaysys.com>

COPYRIGHT
Copyright (c) 2000, 2001, 2002 Perforce Software, Inc. All rights reserved.

See VCP::License ("vcp help license") for the terms of use.