Style Guide

This is a list of preferred styles and conventions for writing code in our humble opinion. It is a work in progress and will be updated as needed.

General Guidelines

Configuration with environment variables

The programs should be configured using environment variables. Check our environment variable list here.

Programs, not plugins

We prefer standalone programs that can be run independently rather than plugins that require a specific host application. If a program requires extension, it should be extensible by writing additional programs.

For example, image you have a program named foo that performs checks on a text. For defining new checks, instead of exposing a plugin API foo should find and call program with a certain name foo__addon for example, and document the API foo__addon should expose.

$ detect_animals (program) (no)
  |--> dogs.so (library)
  '--> cats.so (library)

$ detect_animals (program) (yes)
  |--> detect_animals__dogs (program)
  '--> detect_animals__cats (program)

This way the operator can use any programming language. If the add-ons needed to call some facilities from the program then write a helper program for that. Check definitions.

Programs should support “–help”, “-h”, “-V”, “-v”.

Programs should print a help summary when –help or -h is the first argument. With -V, it should print the configuration. Use -v and $VERBOSE for activating verbose messages.

If possible be getopt(1/3) compatible.

Scripts should support sourcing/inclusion.

Programs written in a scripting language should support being included. This allows to create bundles.

Shell scripts:

if test @"${SCRNAME:-$(basename "$0")}" = @"my-program"; then
    ...
fi

Python scripts:

if __name__ == '__main__':
    ...

Tcl/Tk scripts:

if {[file tail $argv0] eq [file tail [info script]]} {
    ...
}

Print the trace only when `$DEBUG` is set.

Some scripts when failing to read a file, or any other common failure print a trace, it is better to print a concise “Can’t open X” error instead. Print the trace if DEBUG environment variable is set.

A working Makefile or GNUmakefile.

All makefiles shall support all and install. The install target shall not depend on all so that sudo make install works.

If the makefile is POSIX compatible, name it Makefile, otherwise name it GNUmakefile.

All makefiles shall support DESTDIR and PREFIX to specify the installation target.

Scripting programming languages

POSIX Shell programming language.

You should follow the POSIX standard.

The general template:

#!/bin/sh -e
#h: Usage: my-program ...
#h:
#h: Description.
my_program() {
    ...
}
if test @"${SCRNAME:-$(basename "$0")}" = @"my-program"; then
    case "${1}" in
        ''|-h|--help) sed -n 's/^ *#h: \{0,1\}//p' "$0";;
        -V)           true;;
        *)            my_program "$@"; exit 0;;
    esac
fi

In parts:

set -e : All scripts should run with sh -e or set -e so that the program aborts in the first error (as any other sane scripting language).
#h: : Help string.
-V : Prints the environment variables that the program uses.

Command line arguments:

...
my_program() {
    local OPTIND=1 optopt output=
    while getopts "o:" optopt; do # OPTARG
        case $optopt in
            'o') output="$OPTARG";;
            \?)  return 1;;
        esac
    done
    shift $(( $OPTIND - 1 ))
    for arg in "$@"; do
        ...
    done
}
...

Python programming language.

The general template is as follows:

#!/usr/bin/env python3
"""
Usage: my-program ARGS...

description.
"""
import os
import sys

def my_program(arguments):
    ...

if __name__ == '__main__':
    if len(sys.argv) <= 1 or sys.argv[1] in ['-h', '--help']:
        sys.stdout.write(__doc__.strip()+'\n')
        sys.exit(0)
    elif os.getenv('DEBUG') is None:
        try:
            my_program(sys.argv[1:])
        except Exception as err:
            sys.stderr.write('my-program: error: ' + str(err) + '.\n')
            sys.exit(2)
    else:
        my_program(sys.argv[1:])