Lustre Script Coding Style

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 use 8-column tabs and not spaces. For line continuation, an additional tab should be used to indent the continued line, or align after [ or ( for continued logic operations.
• Comments are just as important in a shell script as in C code.
• Use $(...) instead of `...` for subshell commands, since the former is easier to see the start and end of the subshell command, avoids confusion with '...' and a small font, and $(...) can be nested. Use the subshell syntax only when you have to (e.g. when you need to capture the output of a separate program). Using the construct with functions leads to stray output and/or convoluted code struggling to avoid output pollution. It is also more computationally efficient to not fork() the Bash process. Bash is slow enough already.
• Use "here string" like function <<<$var instead of echo $var | function to avoid forking a subshell and pipe
• Use built-in Bash Parameter Expansion for variable/string manipulation rather than forking sed/tr if possible.
• Avoid use of "grep foo | awk '{ print $2 }'" since "awk '/foo/ { print $2 }' works just as well and avoids a separate fork + 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
• Use {1..10} for generating a constant list of integers instead of $(seq 10), though this unfortunately {1..$num} does not work for variable-length lists

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)

• Function arguments should be given local variable names for clarity like "local facet=$1", rather than being used as $1 in the function

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