Shell Programming and Scripting

I've building a bunch of bash scripts, and am thinking about "converting" to perl, and have a couple questions first:

1. Is there anything bash will do that perl won't?
2. How steep is the learning curve?
3. If perl's more powerful, why?
4. I've built a small app in python, which seemed nice, isn't there a wider support depth (i.e. example code, # of users)in perl than python?
5. I'm building mostly sysadmin scripts, if I were going to do more web integration (think php/javascript) with my code, would perl or python be easier to build, and which would be more powerful, or are they roughly the same?

This isn't meant to be a troll, I really would like to continue learning, and you guys have been very helpful learning bash, awk, sed, grep, etc. on multiple occasions

Not really. perl's a more "complete" language. bash is better oriented to scripts. Almost vertical. It's a lot more extensible and supports complex data structures. Perl support seems to be spotty, either very good or very bad. It may be I just never found the right place.

Code:

$ strace bash 2> bash-log
^C
$ strace perl 2> perl-log
^C
$ strace python 2> python-log
^C
$ grep '^open' python-log | wc
    149    1172   13744
tyler@mecgentoo ~ $ grep '^open' perl-log | wc
      9      36     399
tyler@mecgentoo ~ $ grep '^open' bash-log | wc
      7      28     323
tyler@mecgentoo ~ $

Python tries openening 149 files to do nothing at all. For scripts that run once and terminate, python's an absolute pig. For things that stick around, that's tolerable.

I cannot compare Python, as I do not use snakes here. ;-)

Bash is easy and (in version 4) remarkably complete for a shell. Shell scripting starts with automating exactly what you would do on the command-line, so testing is easy. Scripting in a shell usually requires calling external utilities as tools to complete what that shell cannot. My BASH scripts often call ls, rm, grep, find, mv, awk, tr, sed, or other tools.

Perl is far more complete. The syntax is different, and less likely to match what you would do on the command-line. One of its great advantages is that every tool you would call in a script is either built into the Perl interpreter, or is a function that is simple to recreate in Perl. The result is that your Perl script only acts on data, and does not have to call external tools.

I enjoy scripting many things in Bash: in particular scripts that start, stop, or signal services. Since these scripts deal with external services, there is no advantage in using Perl. When I automate something that has only to act and can act faster if external calls are eliminated, I use Perl.

I recommend both, and have never run into a support problem with either. The learning curve is TERRIBLY steep if you feel you have to MASTER perl, because there is a LOT of it! If you only need enough to solve problems in a better, more efficient manner than you can with BASH, then the learning curve is irrelevant: just learn enough to do the job. After using Perl for a few jobs you will find yourself feeling and performing like an expert.

Once you begin learn perl, you will find yourself coding awk, sed, and tr filters far less often. You will even call Perl one-liners from your Bash scripts because they will seem faster and easier to implement.

No language or tool is a total answer to all problems, but the common description of Perl is the "Swiss Army Chainsaw": it cuts all of your problems down to size. You WANT it in your toolbox, you just do not know yet how much.

Perl can do everything BASH can do a lot faster. Perl can also do many things which BASH cannot, e.g. connect to a legion of RDBMS implementations seemlessly with DBI, and support full OO application development.

Many feel it is quite sharp. This is a good place to start: Amazon.com: Learning Perl, 5th Edition (9780596520106): Randal Schwartz, Tom Phoenix, brian d foy: Books


1. Perl's has stronger standard data types, excellent support for references and complex data structures, a rich set of built-in functions and superb support for regular expressions.

2. Perl is much faster than BASH ( but then, so is almost everything else. Time how long it takes both to count to 500,000,000, or to compute a factorial ).

3. Perl has unparalleled 3rd party support with external libraries available from CPAN ( the Comprehensive Perl Archive Network ). For Instance, want to encrypt something with the Whirlpool algorithm? Just use Digest::Whirlpool right out of the box. You would not be so lucky in BASH, Python, or PHP. i.e. you'd be implementing the algorithm on your own.

There are 115 modules in the Digest:: space and 409 modules in Crypt:: compare that to PHP PEAR for instance. It's not even close.

Compare CPAN to Python's Python Package Index : PyPI and you are likely to find CPAN superior. Python really does not have a community-accepted one-stop-shop for all serious 3rd-Party Modules. PHP Pear is much more serious, but it still fails in comparison to CPAN. Knowledge of the pre-existing code on CPAN can make writting applications in Perl Geometrically faster, even without a framework.

Frameworks are where Perl has been weak ( compare, Python Django, Ruby on Rails, or PHP Zend ), until the advent of Catalyst which is a fully featured Perl MVC framework which is catching on very rapidly.

Combine CPAN and Catalyst, and you are really cooking with propane.

Don't build sysadmin scripts in Python or PHP. Use Perl, BASH, awk, sed for those things.

For the Web PHP, Perl, and Python all have strengths and weakness. You could write a thesis on this topic and some do. I'll avoid that.

Summary: despite taking a lot of mostly undeserved guff, Perl remains an excellent choice for everything from one-line one-shot filesystem transforms to full-fledged MVC OO Web Applications.

If you can handle a steep learning curve and *symbolism*, e.g. $# instead of LAST_ELEMENT_IN_THE_ARRAY, Perl will serve you well for many years to come.

Hope That Helps.

A steep learning curve means that more information can be learned over a short time. Most people believe, mistakenly, that a steep learning curve is bad. This probably comes from believing they have to climb it rather than it being a graph of knowledge vs time.

Perl does not have a steep learning curve, i.e. It will take you longer to learn than Bash. Perl has more features, five ways to solve any problem, and CPAN.org which has a module for almost anything you can think of.

Perl is well worth learning as it is a very powerful and flexible language. This is in spite of its NON-steep learning curve.

Please See here, m1xram:

Learning curve - Wikipedia, the free encyclopedia

In particular this:

Spot on on Perl

lol, Wikipedia. It "needs citation" because it is wrong. Would you prefer to learn less over a greater time, with a NON-steep learning curve?



The steeper the curve the more knowledge you get in less time. As the slope approaches infinity you instantaneously know more. Think Matrix upload to your brain.

I wish people would stop using this term, it's embarrassing.