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Dividing the Linux desktop
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A report from pgCon 2013
Scripting languages come and go, and the modern one break their own scripts every five years. Shell (without bashisms) seems to be as close to eternal as the computer industry can manage.
Use the right tool for the job.
Posted Dec 7, 2012 22:02 UTC (Fri) by davidescott (guest, #58580)
Not so sure about that. Trying to run a shell script on an older sysv system I think bash-isms are the least of your problems. Consider all the gnu-isms in the commands you use every day.
Compare the single unix specification ls (copyright is only 11 years ago):
to gnu ls:
-A, --author, -b (aka --escape), --block-size, -B (--ignore-backups), --color, -D, --file-type, --format, --full-time, -G, -h, --si, --dereference-command-line-symlink-to-dir, --hide, --indicator-style, -I, -k, -N (--literal), --show-control-chars, -Q, --quoting-style, -R, -S, --sort, --time, --time-style, -T, -U, -v, -w, -X
If you think about POSIX sh as the "core language" and all the programs in /usr/bin as the "libraries" for that language, then shell has seen a very stable core language and a massive expansion in the number and variety of libraries. On the other hand languages like ruby/python/etc have evolved more evenly across the language/library split.
"Shell is universally understood" has more to do with the overwhelming success of the GNU system and the power of open-source to push out the inferior closed source versions. Not that shell programming has been completely static.
Posted Dec 7, 2012 22:07 UTC (Fri) by dlang (✭ supporter ✭, #313)
If you take a shell script from 20 years ago, the odds of it being able to run on a system today are very high
Perl is also fairly good about backwards compatibility, but I don't know how far back Perl 5 goes.
most other languages are far worse, and if you take a program written in them 10-15 years ago (if they were even around that long), the odds are very poor that you could run the program today without going through a porting effort that would be comparable to porting to a different language.
Posted Dec 8, 2012 1:35 UTC (Sat) by Cyberax (✭ supporter ✭, #52523)
I've recently spent 5 hours rewriting old scripts from a long ago retired Sun box. Searching old manuals to understand what non-standard command line options do is such a great way to spend time. Especially when it's not possible to simply run them.
Posted Dec 8, 2012 2:05 UTC (Sat) by sitaram (subscriber, #5959)
As for non-standard options, I suspect most of the Sun utilities would be closer to BSD.
Posted Dec 8, 2012 2:11 UTC (Sat) by Cyberax (✭ supporter ✭, #52523)
On the other hand, I've ported 15-year old Python scripts without much problems. There were several non-backward-compatible changes in Python since then, but they are fairly minor.
Posted Dec 8, 2012 6:53 UTC (Sat) by mathstuf (subscriber, #69389)
For Python, one I hit today was to change "except BaseException as e:" to "except BaseException: e = sys.exc_info()" to support 2.4 through 3.2 in the same script. A little annoying, but not as pretty as either just-one-way canonical syntax.
As for shell, we found out that BSD sed and GNU sed don't support compatible -i flags. BSD requires a suffix, GNU requires there be no space if one is given, which BSD rejects. Using manual .bak files feels worse than either by a long shot. I think the call has been replaced by awk instead now.
In my experience, GNUisms tend to be harder to work around than Python incompatibilities. That's why I try to avoid them in my shell scripts. Unfortunately, sed -i is very convenient and sponge just isn't common enough, but this is slowly being trained out of my fingers when I'm in "portable" mode (I use every trick I can at the prompt, just not when writing .sh files).
Commands on an old Sun box
Posted Dec 10, 2012 7:19 UTC (Mon) by jrn (subscriber, #64214)
Posted Dec 10, 2012 14:17 UTC (Mon) by Cyberax (✭ supporter ✭, #52523)
In any case, I was interested in a rewrite in a sane language, not just running these scripts.
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