Keeping Track of Change
RCS doesn't keep a whole new copy of the file each time you check in changes. Instead, it records only the lines with changes in them, along with the descriptions of the changes (if you choose to provide them). It does this in a separate file. Changes to the file filename are kept in the file filename,v. If you find this to be too much clutter, you can tell RCS to stash the filename,v file out of the way, in a subdirectory called RCS. Simply create the subdirectory, and RCS will automatically use it.
Remember what it looked like when the foo file was checked in, above? Let's create a bar file whose corresponding bar,v file is kept out of sight in an RCS directory:
$ mkdir RCS $ vi bar $ ci -l bar RCS/bar,v <--bar enter description, terminated with single '.' or end of file: NOTE: This is NOT the log message! > $ vi bar $ ci -l bar RCS/bar,v <-- bar new revision: 1.2; previous revision: 1.1 enter log message, terminated with single '.' or end of file: >
If you did not originally create an RCS directory, and you get tired of seeing the ,v files, you can use these commands to get them out of the way safely:
$ mkdir RCS $ mv *,v RCS
RCS will know where to search for them.
So what do you do when you screw up? You have carefully kept copies of your changes, but how do you retrieve yesterday's version, or last year's version, or the second most recent version?
RCS keeps track of versions by version numbers. The first version you check in is assigned the number 1.1, the second is assigned the number 1.2, the third 1.3, and so on.
When you find that you have made a mistake, you can compare what you currently have with previous revisions. To compare against the previous revision, use this command:
$ rcsdiff -u filename
The -u tells rcsdiff to use the “unified diff” format to show you the changes, and it compares the current version of the file filename with the most recent version that was checked in. Here's an example. The previously checked in version of the file foo, version 1.3, consisted of:
This is a test of the emergency RCS system. This is only a test.
I have since edited the current version to read:
This is a test of the emergency RCS version control system. This is only a test.
Before checking this new version in, I can check the differences between the current contents of the file and the previous version that was checked in, giving me this:
$ rcsdiff -u foo ============================================== RCS file: foo,v retrieving revision 1.3 diff -u -r1.3 foo --- foo 1996/02/01 00:34:15 1.3 +++ foo 1996/02/01 00:34:31 @@ -1,2 +1,3 @@ This is a test of the emergency -RCS system. This is only a test. +RCS version control system. +This is only a test.
After showing what versions are being compared, the differences are shown. Lines that have not been changed are printed with a single space in front of them. Lines that have been removed in the newer version have a - in front of them, and lines that have been added have a + in front of them. As you can see, lines that are changed are considered to be deleted from the older version, and changed replacements added to the new version. Around any section with changed line, up to 3 lines of unchanged “context” will be shown to help you understand where in the file the change has been made.
This mechanism can be used to compare any two versions. After making a few more changes to the file, I can compare revision 1.6 to revision 1.3:
$ rcsdiff -u -r1.3 -r1.6 foo ============================================== RCS file: foo,v retrieving revision 1.3 retrieving revision 1.6 diff -u -r1.3 -r1.6 -- foo 1996/02/01 00:34:15 1.3 +++ foo 1996/02/01 01:05:28 1.6 @@ -1,2 +1,6 @@ This is a test of the emergency -RCS system. This is only a test. +RCS version control system. +This is only a test. + +I'm now adding a few lines for +the next version.
Note that it is good to list the earlier revision first. Otherwise, the sense of + and - are reversed.
Your changes are likely to be much more significant than these examples, and may take up more than a screen listing. This is not a problem; use a pager to view your output one screenful at a time:
$ rcsdiff -u -r1.3 -r1.6 foo | less
Once you see the changes you have made, you can usually figure out where you made your mistake and fix it by hand. Sometimes you might have accidentally done damage that is large and confusing, but more often you have changed a phrase or a paragraph, are dissatisfied with your change, and simply can't remember exactly what it used to look like.
If you want to, you can store a copy of the changes in a file with a command like:
$ rcsdiff -u -r1.3 -r1.6 foo > filename
or print the changes like:
$ rcsdiff -u -r1.3 -r1.6 foo | lpr
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- The Firebird Project's Firebird Relational Database
- Stunnel Security for Oracle
- My +1 Sword of Productivity
- SUSE LLC's SUSE Manager
- Non-Linux FOSS: Caffeine!
- Managing Linux Using Puppet
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Parsing an RSS News Feed with a Bash Script
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide