Lustre Script Coding Style

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Bash Style

  • Bash is a programming language. It includes functions. Shell code outside of functions is effectively code in an implicit main() function. An entire function should be fully seen on one page (~70-90 lines) and be readily comprehensible. If you have any doubts, then it is too complicated. Make it easier to understand by separating it into subroutines.
  • The total length of a line (including comment) must not exceed 80 characters. Take advantage of bash's += operator for constants or linefeed escapes \.
  • Lines can be split without the need for a linefeed escape after |, ||, & and && operators.
  • The indentation must 8-column tabs and not spaces. For line continuation, an additional tab should be used to indent the continued line.
  • Comments are just as important in a shell script as in C code.
  • Use $(...) instead of `...` for subshell, but avoid them if you can. Text results from functions should be put into a well-named variable. Use the subshell syntax only when you have to (e.g. when you need to capture the output of a separate program). Using the construct with functions leads to stray output and/or convoluted code struggling to avoid output pollution. It is also more computationally efficient to not fork() the BASH process. BASH is slow enough already. `...` is obsolete and $(...) is easier to see the start and end of the subshell command, avoids confusion with '...' and a small font, and $(...) can be nested.
  • Use "here string" like function <<<$var instead of echo $var | function to avoid forking a subshell and pipe
  • If a variable is intended to be used as a boolean, then it must be assigned as followed:
local mybool=false         # or true
if $mybool; then
        do_stuff
fi
 
  • for loops it is possible to avoid a subshell for $(seq 10) using the built-in iterator for fixed-length loops (unfortunately, {1..$var} does not work):
for i in {1..10}; do
      something_with $i
done

  • Use export FOOBAR=val instead of FOOBAR=val; export FOOBAR for clarity and simplicity
  • Use [[ expr ]] instead of [ expr ], especially since the [[ test understands regular expression matching with the =~ operator. The easiest way to use it is by putting the RE in a variable and expanding the RE after the operator without quotes.
  • Use $((...)) for arithmetic expressions instead of expr

Test Framework

Variables

  • Names of variables local to current script which are not exported to the environment should be declared with "local" and use lowercase letters
  • Names of global variables or variables that exported to the environment should be uppercase letters

Functions

  • Each function must have a section describing what it does and explain the list of parameters
# One line description of this function's purpose
#
# More detailed description of what the function is doing if necessary
#
# usage: function_name [--option argument] {required_argument} ...
# option: meaning of "option" and its argument
# required_argument: meaning of "required_argument"
# 
# expected output and/or return value(s)

Tests and Libraries

  • To avoid clustering a single test-framework.sh file, there should be a <test-lib>.sh file for each test that contains specific functions and variables for that test.
  • Any functions, variables that global to all tests should be put in test-framework.sh
  • A test file only need to source test-framework.sh and necessary <test-lib>.sh file