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1 Miscellaneous Commands and Features of VC

This section explains the less-frequently-used features of VC.


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1.1 Change Logs and VC

If you use RCS or CVS for a program with a ‘ChangeLog’ file (@pxref{Change Log}), you can generate change log entries from the version control log entries of previous commits.

Note that this only works with RCS or CVS. This procedure would be particularly incorrect on a modern changeset-based version control system, where changes to the ‘ChangeLog’ file would normally be committed as part of a changeset. In that case, you should write the change log entries first, then pull them into the ‘*vc-log*’ buffer when you commit (@pxref{Log Buffer}).

C-x v a

Visit the current directory’s ‘ChangeLog’ file and, for registered files in that directory, create new entries for versions committed since the most recent change log entry (vc-update-change-log).

C-u C-x v a

As above, but only find entries for the current buffer’s file.

For example, suppose the first line of ‘ChangeLog’ is dated 1999-04-10, and that the only check-in since then was by Nathaniel Bowditch to ‘rcs2log’ on 1999-05-22 with log entry ‘Ignore log messages that start with '#'.’. Then C-x v a inserts this ‘ChangeLog’ entry:

1999-05-22  Nathaniel Bowditch  <nat@apn.org>

        * rcs2log: Ignore log messages that start with '#'.

If the version control log entry specifies a function name (in parenthesis at the beginning of a line), that is reflected in the ‘ChangeLog’ entry. For example, if a log entry for ‘vc.el’ is ‘(vc-do-command): Check call-process status.’, the ‘ChangeLog’ entry is:

1999-05-06  Nathaniel Bowditch  <nat@apn.org>

        * vc.el (vc-do-command): Check call-process status.

When C-x v a adds several change log entries at once, it groups related log entries together if they all are checked in by the same author at nearly the same time. If the log entries for several such files all have the same text, it coalesces them into a single entry.


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1.2 Deleting and Renaming Version-Controlled Files

M-x vc-delete-file

Prompt for a file name, delete the file from the working tree, and schedule the deletion for committing.

M-x vc-rename-file

Prompt for two file names, old and new, rename them in the working tree, and schedule the renaming for committing. The old file defaults to the current buffer’s file name if it is under VC.

If you wish to delete a version-controlled file, use the command M-x vc-delete-file. This prompts for the file name, and deletes it via the version control system. The file is removed from the working tree, and in the VC Directory buffer (@pxref{VC Directory Mode}), it is displayed with the ‘removed’ status. When you commit it, the deletion takes effect in the repository.

To rename a version-controlled file, type M-x vc-rename-file. This prompts for two arguments: the name of the file you wish to rename, and the new name; then it performs the renaming via the version control system. The renaming takes effect immediately in the working tree, and takes effect in the repository when you commit the renamed file.

On modern version control systems that have built-in support for renaming, the renamed file retains the full change history of the original file. On CVS and older version control systems, the vc-rename-file command actually works by creating a copy of the old file under the new name, registering it, and deleting the old file. In this case, the change history is not preserved.


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1.3 Revision Tags

Most version control systems allow you to apply a revision tag to a specific version of a version-controlled tree. On modern changeset-based version control systems, a revision tag is simply a symbolic name for a particular revision. On older file-based systems like CVS, each tag is added to the entire set of version-controlled files, allowing them to be handled as a unit. Revision tags are commonly used to identify releases that are distributed to users.

There are two basic commands for tags; one makes a tag with a given name, the other retrieves a named tag.

C-x v s name <RET>

Define the working revision of every registered file in or under the current directory as a tag named name (vc-create-tag).

C-x v r name <RET>

For all registered files at or below the current directory level, retrieve the tagged revision name. This command will switch to a branch if name is a branch name and your VCS distinguishes branches from tags. (vc-retrieve-tag).

This command reports an error if any files are locked at or below the current directory, without changing anything; this is to avoid overwriting work in progress.

You can give a tag or branch name as an argument to C-x v = or C-x v ~ (@pxref{Old Revisions}). Thus, you can use it to compare a tagged version against the current files, or two tagged versions against each other.

On SCCS, VC implements tags itself; these tags are visible only through VC. Most later systems (including CVS, Subversion, bzr, git, and hg) have a native tag facility, and VC uses it where available; those tags will be visible even when you bypass VC.

In file-based version control systems, when you rename a registered file you need to rename its master along with it; the command vc-rename-file will do this automatically (see section Deleting and Renaming Version-Controlled Files). If you are using SCCS, you must also update the records of the tag, to mention the file by its new name (vc-rename-file does this, too). An old tag that refers to a master file that no longer exists under the recorded name is invalid; VC can no longer retrieve it. It would be beyond the scope of this manual to explain enough about RCS and SCCS to explain how to update the tags by hand. Using vc-rename-file makes the tag remain valid for retrieval, but it does not solve all problems. For example, some of the files in your program probably refer to others by name. At the very least, the makefile probably mentions the file that you renamed. If you retrieve an old tag, the renamed file is retrieved under its new name, which is not the name that the makefile expects. So the program won’t really work as retrieved.


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1.4 Inserting Version Control Headers

On Subversion, CVS, RCS, and SCCS, you can put certain special strings called version headers into a work file. When the file is committed, the version control system automatically puts the revision number, the name of the user who made the commit, and other relevant information into the version header.

VC does not normally use the information in the version headers. As an exception, when using RCS, Emacs uses the version header, if there is one, to determine the file version, since it is often more reliable than the RCS master file. To inhibit using the version header this way, change the variable vc-consult-headers to nil. VC then always uses the file permissions (if it is supposed to trust them), or else checks the master file.

To insert a suitable header string into the current buffer, use the command M-x vc-insert-headers. This command works only on Subversion, CVS, RCS, and SCCS. The variable vc-backend-header contains the list of keywords to insert into the version header; for instance, CVS uses vc-cvs-header, whose default value is '("\$Id\$"). (The extra backslashes prevent the string constant from being interpreted as a header, if the Emacs Lisp file defining it is maintained with version control.) The vc-insert-headers command inserts each keyword in the list on a new line at point, surrounded by tabs, and inside comment delimiters if necessary.

The variable vc-static-header-alist specifies further strings to add based on the name of the buffer. Its value should be a list of elements of the form (regexp . format). Whenever regexp matches the buffer name, format is also inserted as part of the version header. A ‘%s’ in format is replaced with the file’s version control type.


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2 Customizing VC

The variable vc-handled-backends determines which version control systems VC should handle. The default value is (RCS CVS SVN SCCS SRC Bzr Git Hg Mtn), so it contains all the version systems that are currently supported. If you want VC to ignore one or more of these systems, exclude its name from the list. To disable VC entirely, set this variable to nil.

The order of systems in the list is significant: when you visit a file registered in more than one system, VC uses the system that comes first in vc-handled-backends by default. The order is also significant when you register a file for the first time (@pxref{Registering}).


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2.1 General Options

Emacs normally does not save backup files for source files that are maintained with version control. If you want to make backup files even for files that use version control, set the variable vc-make-backup-files to a non-nil value.

Editing a version-controlled file through a symbolic link may cause unexpected results, if you are unaware that the underlying file is version-controlled. The variable vc-follow-symlinks controls what Emacs does if you try to visit a symbolic link pointing to a version-controlled file. If the value is ask (the default), Emacs asks for confirmation. If it is nil, Emacs just displays a warning message. If it is t, Emacs automatically follows the link and visits the real file instead.

If vc-suppress-confirm is non-nil, then C-x v v and C-x v i can save the current buffer without asking, and C-x v u also operates without asking for confirmation.

VC mode does much of its work by running the shell commands for the appropriate version control system. If vc-command-messages is non-nil, VC displays messages to indicate which shell commands it runs, and additional messages when the commands finish.


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2.2 Options for RCS and SCCS

By default, RCS uses locking to coordinate the activities of several users, but there is a mode called non-strict locking in which you can check-in changes without locking the file first. Use ‘rcs -U’ to switch to non-strict locking for a particular file, see the rcs manual page for details.

When deducing the version control state of an RCS file, VC first looks for an RCS version header string in the file (see section Inserting Version Control Headers). If there is no header string, VC normally looks at the file permissions of the work file; this is fast. But there might be situations when the file permissions cannot be trusted. In this case the master file has to be consulted, which is rather expensive. Also the master file can only tell you if there’s any lock on the file, but not whether your work file really contains that locked version.

You can tell VC not to use version headers to determine the file status by setting vc-consult-headers to nil. VC then always uses the file permissions (if it is supposed to trust them), or else checks the master file.

VC determines the version control state of files under SCCS much as with RCS. It does not consider SCCS version headers, though. Thus, the variable vc-consult-headers does not affect SCCS use.


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2.3 Options specific for CVS

You can specify additional command line options to pass to all CVS operations in the variable vc-cvs-global-switches. These switches are inserted immediately after the cvs command, before the name of the operation to invoke.

When using a CVS repository on a remote machine, VC can try keeping network interactions to a minimum. This is controlled by the variable vc-cvs-stay-local. If vc-cvs-stay-local is only-file (the default), VC determines the version control status of each file using only the entry in the local CVS subdirectory and the information returned by previous CVS commands. As a consequence, if you have modified a file and somebody else has checked in other changes, you will not be notified of the conflict until you try to commit.

If you change vc-cvs-stay-local to nil, VC queries the remote repository before it decides what to do in vc-next-action (C-x v v), just as it does for local repositories.

You can also set vc-cvs-stay-local to a regular expression that is matched against the repository host name; VC then stays local only for repositories from hosts that match the pattern.

When using a remote repository, Emacs normally makes automatic version backups of the original versions of each edited file. These local backups are made whenever you save the first changes to a file, and they are removed after you commit your changes to the repository. (Note that these are not the same as ordinary Emacs backup files; @pxref{Backup}.) Commands like C-x v = and C-x v u make use of automatic version backups, if possible, to avoid having to access the network.

Setting vc-cvs-stay-local to nil disables the making of automatic version backups.

Automatic version backups have names of the form file.~version.~. This is similar to the name that C-x v ~ saves old versions to (@pxref{Old Revisions}), except for the additional dot (‘.’) after the version. The relevant VC commands can use both kinds of version backups. The main difference is that the manual version backups made by C-x v ~ are not deleted automatically when you commit.

CVS does not use locking by default, but there are ways to enable locking-like behavior using its CVSREAD or watch feature; see the CVS documentation for details. If that case, you can use C-x v v in Emacs to toggle locking, as you would for a locking-based version control system (@pxref{VC With A Locking VCS}).


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