Linux command: Side by side diff
Every now and then I come across a feature of some Linux command that works so well that I have trouble understanding how I managed without it for so long. The one that I most recently discovered is the side by side option for the diff command.
Sure, the designations that diff offers to identify differences between two files are useful. But I don't find them particularly intuitive.
# diff frogs frogs2
7,8c7,8
< Canyon Treefrog
< (Hyla arenicolor)
---
> Florida Cricket Frog
> (Acris gryllus dorsalis)
28,30d27
< Western Chorus Frog
< (Pseudacris triseriata triseriata)
<
33a31,33
> Southern Chorus Frog
> (Pseudacris nigrita nigrita)
>
35a36,38
>
> Little Grass Frog
> (Pseudacris ocularis)
The standard diff output is meant to be terse. It captures the differences between two files in such a way as to make it possible to convert one file to the other if you only end up with one of them. The "7,8c7,8" string, for example, captures the fact that lines 7 and 8 are different between the two files. If you want to turn frogs into frogs2, you exchange the following two lines with two following the "---". To turn frogs2 into frogs, you do the reverse. One way to keep many generations of an important file without duplicating most of the content over and over again would to be to save the diffs.
If you are only interested in whether the files are different, you can throw away the output from the diff command (i.e., send it to /dev/null) and look at $? (the return code). If the files are different, $? will be set to 1. Alternately, you could use the simpler cmp command which reports the first difference between the two files and then stops.
The side by side equivalent of this output is more wordy, but I instantly understand the nature and extent of the differences. The vertical bar ("|") characters point out differences between the two files while the "<" and ">" characters note where content appears in only one or the other of the two files.
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Solaris has always (?) had sdiff
It is not really necessary to add diffutils to Solaris for side-by-side diff comparisons. It may be useful for consistency in scripts, but side-by-side diff is more of a human interface and not really a scripting tool.I have been using Solaris (on SPARC) for about 13 years (and SunOS before that). It has always had sdiff. I can't remember if it was in SunOS since that was a while ago.
As I recall, sdiff was used under the graphical interface for WorkShop (the compiler tools).
Gerard
tkdiff
As always I enjoyed your article Sandra. Just wanted to add I've come to really like using tkdiff, a very nice graphical wrapper around diff that is very portable. I found it here http://sourceforge.net/projects/tkdiff .Mac OS X Users
Great article Sandra, as always. For Mac OS X users can use opendiff command. it opens files in graphical environment and points out the differences.