Swapping languages on CodinGame (a.k.a. system() calls)


Calling an interpreter from Bash

We can call different interpreters with a one-liner solution passed as a command-line parameter directly from bash.

Unfortunatelly, we need to escape any dollar signs $, double quotes " and backslashes \ in our source code (by adding a backslash \ before them). This hurts especially in Perl and PHP, where all variable names start with a $ sign... At least, in some languages single quotes ' can be used instead of double quotes " (although in PHP with slightly different meaning).

Note: All the examples provided would try to read the test cases as input. That would not work on, therefore these coding examples are not runnable here. You can try them out in the CG IDE for the Rubik puzzle.

Base solution

My base solution for the sample puzzle is 34 characters long in Bash.

# ===== Bash
#   length = base [34] = 34 chars
read n;echo $((n>1?6*n*(n-2)+8:1))


# ===== to Perl from Bash
#   length = 9 + base [38] + #vars [4] = 51 chars
#   $ in variable names must be escaped...
perl -e"my\$n=<STDIN>;print\$n>1?6*\$n*(\$n-2)+8:1"

My Perl solution is 38 chars. Calling the interpreter adds 9 chars, escaping adds another 4 extra chars in this tiny example.


# ===== to PHP from Bash
#   length = 8 + base [41] + #vars [4] = 53 chars
#   $ in variable names must be escaped...
php -r"\$n=fgets(STDIN);echo\$n>1?6*\$n*(\$n-2)+8:1;"

My PHP solution is 41 chars. Calling the interpreter adds 8 chars, escaping adds 4.


# ===== to Python from Bash
#   length = 12 + base [47] = 59 chars
#   use python instead of python3 to invoke Python 2.x
python3 -c"n=int(input());print(6*n*(n-2)+8 if n>1 else 1)"

My Python solution is 47 chars. Calling the interpreter adds 12 chars. Here I did not need any escaping.

Note: using python instead of python3 saves 1 char, but it still invokes Python 2.x on CG, so your code might not be backwards compatible.


# ===== to Ruby from Bash
#   length = 24 + base [34] = 58 chars
#   calling ruby without the full path no longer works...
/usr/local/bin/ruby -e"n=gets.to_i;puts n>1?6*n*(n-2)+8:1"

My Ruby solution is 34 chars. Currently ruby seems to be not in the $PATH on CG, so we need to add full path which costs 24 chars for invoking the interpreter.

Coming next...

Starting from bash is not always what we need. How to do similar system calls from other languages?

Create your playground on
This playground was created on, our hands-on, knowledge-sharing platform for developers.
Go to
codingame x discord
Join the CodinGame community on Discord to chat about puzzle contributions, challenges, streams, blog articles - all that good stuff!
Online Participants