The myth of the small script
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The document discusses how tasks that seem simple can actually be more complicated. It describes a boss asking an employee to write a short script to print the 3rd and 5th columns of a file. The employee writes a basic script but discovers it has issues, such as requiring a filename parameter and not handling different field separators. The script is improved with input checking and help functionality. The document concludes that "small scripts" often require more work, and it's better to use a general-purpose language like Java that can support more use cases and operating systems.
![The First Amendment
$ cat ./my_short_script_v2.sh
#!/bin/bash
function help {
echo "Please run the script as follow example:"
echo ""
echo "$ $1 <data_file_name>"
echo ""
echo "<data_file_name>: as the name of a csv file in data folder"
echo ""
echo ""
}
if [ "$#" -ne 1 ]; then
help $0;
exit 0
fi
data="./data"
cut -f 3,5 -d , ${data}/$1](https://image.slidesharecdn.com/themythofthesmallscript-160516153524/85/The-myth-of-the-small-script-10-320.jpg)
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The myth of the small script
- 1. The myth of the small script Mario A. Santini - Full Stack Developer JUG TAA
- 2. The Mith Of The Small Script This is a story about how what seemed a simple problem, actually is rather complicated
- 3. A New Task • Your boss: “Please, write a small script that prints out the 3rd and the 5th column of this file.” • Your boss: “Keep in mind, I need it: ASAP!”
- 4. Have A Deep Look At The Task • Looks as an easy and short task, but actually you missed some important infos. • Most of the requirements or client expectations arrive like this. • It is simple for your boss, just because it’s easy to explain. Of course if you don’t go deep inside the details. Actually software is made by details!
- 5. Remember, We Don’t Have Time • On those situations it is better for you to go back to your boss with something to show, and not with something to ask about. • So we guess the missed details and do our best!
- 6. The Script - Requirements • We know we have a text file divided in columns to parse • We guess the files are on a Linux server • We guess just to printout the result • The fast and easy way is to write a very short shell script in bash
- 7. The Script - The Code $ cat ./my_short_script.sh <<EOF > #!/bin/bash > > data="./data" > > cut -f 3,5 -d , ${data}/$1 > > EOF $ chmod a+x ./my_short_script.sh >>> Test it! $ ./my_short_script.sh the_file_to_compute.cv head3,head5 field3,field5 field3,field5 field3,field5 field3,field5 field3,field5 field3,field5 field3,field5 field3,field5 … Pretty easy, pretty fast!
- 8. The Script Doesn’t Work! • Your boss: “Sorry, I launched your script and got an error: “ cut: Error reading ./data/ … after a complicated interview with your boss… • You: “You miss the parameter, that’s why the script fail” • Your boss: “Sorry man, I don’t know anything about a parameter”
- 9. The First Amendment • Add a simple help • Check if the data file is in input, if not print the help You don’t know how people will use your code!
- 10. The First Amendment $ cat ./my_short_script_v2.sh #!/bin/bash function help { echo "Please run the script as follow example:" echo "" echo "$ $1 <data_file_name>" echo "" echo "<data_file_name>: as the name of a csv file in data folder" echo "" echo "" } if [ "$#" -ne 1 ]; then help $0; exit 0 fi data="./data" cut -f 3,5 -d , ${data}/$1
- 11. The Second Amendment • Your boss: “It works with few files, but some times I got an error, could you have a look please?” • After a little investigation you have: • your script doesn’t support fields that contains the field separator, even if they are quoted and valid csv files; • your script doesn’t support different field separator characters.
- 12. Now Works But… • Your boss: “In some files, we need to print out the 2nd and the 4th columns, instead of the 3rd and the 5th.” Things changes!
- 13. A New Improovement • Your boss: “I would like to work at home, but I don’t have any other Unix like Oss there.”
- 14. Possible Solutions • Docker / Vagrant … it’s a bunch of gigs and more headaches for the future… • Cygwin… No thanks… too complicated for my boss. The better solution is to re-write your script in a way that it is more easy to manage: use a general purpose programming language like Java ( Of course you could use your preferred language to, but remember, we are a Jug! ;) )
- 15. What “Like Java” means • a powerful general purpose language • could run on many different operating systems without needs of changes on the source code • have a long list of available libraries that helps writing less code and doing things fast and safe • supported from a wide and huge community • Last but not last: to be Open Source, better if FOSS
- 16. What We Need In order to re-write the script in Java, we could even use a short cut by including useful libraries: • A lib to handle csv files • A lib to handle command line options • An installing framework tool • A lib for log
- 17. Conclusions In the real word you never have something as “a small script”. Even if you are a developer like me, and you have your HD full of small scripts doing everything you need to be done.
- 18. Conclusions 2 The scripts you write for yourself are simple because you don’t have to deal with many choices, you just design it as it perfectly fits your needs. And more, you fits the world to fits your script. If your needs will changes, you know it and you’ll change the scripts first or adapt the environment as convenient.
- 19. Conclusion 3 Don’t be afraid to use general purpose languages like Java. They are so widely spread because you could use it for short programs, like the one we shown you, to very complicated systems made by millions of line of code. So think it easy and simple as KISS wants, but not be trivial.
- 21. Thank you!