Shell Script Language – Use Perl, Not Bash

In your example, you seem to be using -eq instead of != just to make Bash seem more foreign.

Unlike perl you generally don’t have to install anything extra on your system for BASH

Is there an easy way to do the following in PERL? Because in BASH doing operations on multiple files at once is very easy.

The below will also work with filenames with strange characters in their name; it will figure out the escape characters for you so passing in the filenames to another program is no trouble.

for x in /home/*; do
echo $x
done

Is there an easy way of telling if a file/directory exists using Perl?

# use -d for directories
if [ -e /tmp/file.txt ]; then
echo “file.txt exists”
fi

PERL is a nice language, but there is no reason to use it over BASH for automated tasks.

uups, in the first example my angle brackets disappeared..
it should read

print “$_\n” for (/home/*);

and now replace the round brackets with angle ones 😉

>I still use bash to write shell scripts – but if the shell script has an if condition(other than a simple argument check), I use a higher language – usually Perl.

I agree with you about using a higher language for more complicated scripts. Regarding the language, I prefer Python.

Will: In the shell, using -eq forces a numeric comparison v/s using ==, which does a string comparison. It’s better to use the -eq/-ne versions in the shell when comparing numbers. It’s slightly faster, and will generate a warning if non-numeric input is presented.

To counter the argument that perl looks better, consider a case statement in the shell – that has to be a big if/elsif/else block in perl, since perl has no case statement (yeah, there’s a non-standard module which sortof adds a case-like structure). There’s no perl equivalent which looks better than this shell code.

case $var in
1 ) print “var is one” ;;
2 ) print “var is two” ;;
* ) print “var is not one or two” ;;
esac

In any event…

I use the shell (ksh, usually, but Bash is fine) for operations which involve a lot of system calls (automating processes) or looking at filenames. I use perl if I’m doing more than a quick grep on files or anything more involved – though one can do some pretty complicated things if one looks into the shell’s more advanced capabilities. They’re two different tools, and each has an area in which they’re the better choice. Much as I love perl (and I was a proessional perl developer for a while), the shell has its niche. 🙂

Hi Binny, thanks for the post — very imformative.

As part of my career advancement with my current testing of software applications that sit on top of linux, I am learning scripting using Python — b/c that is the High Level Language the Lead Software developer on our team evangelizes.

If it is worth you writing a post that compares the major High Level Languages, then I would love to see it.

Sounds like, in the future, I might also desire to then learn some scripting in straight bash.

My sitting in the lab for one-hour-plus, manually grepping for “errors” on log file results from an overnight test, is getting boring.

“I’m feeling the pain, so I’m seeing the light.”

Hi Binny
Any updates would really appreciated..

raw_data array is assigned to handler.
i.e @raw_data=handler;

Hello,

I have a question. I use shell script (bash, ksh, etc.) to automate a lot of things like grouping all OS commands together and run them in a script. For example, in an Oracle RAC environment running on Linux, I use srvctl extensively for adding and removing services, etc. If I use perl, how can I do this? Please give examples as I do not know Perl well.

Regards,

Thanks BinnyVA.

Nice explanation.

http://unstableme.blogspot.com/search/label/Bash

Every unix sysadmin should be well versed in shell scripting. It’s mandatory. For that same group of people, perl is not mandatory, but a very nice to have. Take a look at the OS init scripts. They’re all shell scripts. These are the kinds of scripts sysadmins work with the great majority of the time. Yes, there are times when perl makes more sense, but I would say this is rare…for the sysadmin crowd. If you’re a sysadmin, look at any decent init script. If you can’t write something similar…with the same level of difficulty/elegance, you need to improve your shell scripting skills. Another aspect to keep in mind is shell scripting is basically just blocks of system commands. As a sysadmin, the better you can shell script, the better you are at the command line and vice versa. A sysadmin spends most of his time operating on the commandline. You might as well write as much of your scripts in bash as possible to complement your commandline skills.

I have written a complete system for automatization in Bash:
-> Basic Mechanism: SSH/SCP remote scripting through expect to machine’s lists and SQL scripts launch.
-> Intepreters: build bash scripts based on tag language that will be launched by the basic mechanism.

For me, it was a painful experience, especially character mapping and so on. I solved this issue using temporal files with bash environment on it.

It took me a whole year to have something functional (tag definition language).

Bash is a requirement in my enviroment but I was wondering, is there any other tool that simplifies the stuff. Bash is really painful. The core, right now, is working beutifully due to it’s simplicity. But it is a challenge to code a whole project (with modules, and so on).

Another thing is that it is difficult to parallized task keeping a clear execution path. Using nohup with counters to know if all processes ended.

As a conclusion: bash can be fine for little scripts only. I guess perl and so on allow you to manage threads and stuff like that and have a logger (you don’t have to build your own logger), to make it faster, and, hopefully, faster development.

Any ideas? It is working fine right now, and it is flexible to extend since each module do very little things. But each platform brings new stuff to change, particulary the character mapping and so on.

Thanks,

Cesar

As a contractor that values job duration over value, I much more prefer bash:) Honestly, these kids today checkout one my bash scripts and their heads just about fall off!

Does this satisfy the request?

sed ‘s/oldText/newTest/g’ outfile.txt

All nonsense, real men use csh. 😉

Good discussions/brainstorming about perl vs bash scripting. One comment I have is about the “strict” variable checking in Perl. By using “use strict”, we can force perl to do strict variable checking i.e. if a variable is erroneously used (and it wasn’t created in the first place), perl would loudly complain. This is very useful during development and to eliminate all those typos that could crrep into your code.

I am wondering if there is a equivalent feature in bash? For example in bash if I do a typo in one of the variables I intend to use, bash would happily go on without complaining. But this would lead to serious and very hard to find bugs in the code, since the variable with the typo wasn’t defined in the first place. I have struggled with this issue in bash.

So still my question is, is there a way to do strict variable checking in shell scripts (particularly bash)? If not that is a major problem.

Raj – I prefer to use
set -o nounset
(which I think is more readable / self-documenting). 🙂

You probably also want to look into the “typeset -i” (and synonymous “integer”) builtin, which will treat a variable as a number and throw an error if you attempt to store a non-numeric value.

The “set -o errexit” command is also useful, as that will cause your script to exit if any command fails without being trapped (by “trapped” I mean not the conditional in an if statement or of the form “command || action”).

I totally agree with VU as a sysadmin I run into shell scripts *all* the time.

I do not have a developers background and I found myself really enjoying writing -scripts in bash. Like VU said it is chunks of command line mixed in with some cool logic.

Then as the scripts got more and more complex I often find myself pulling at hair that is just not there. I often joke that if I had a mortal enemy I would call him syntax.

Now I am left wondering if I should learn a higher level language, would that help or confuse things. As I do feel mostly comfortable with bash scripting but often still run into hurdles.