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.
- Lines can be split without the need for a linefeed escape after
- 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
$(...)
instead of`...`
for subshell commands:$(...)
is easier to see the start and end of the subshell command$(...)
avoids confusion between'...'
and`...`
with a small font$(...)
can be nested
- Use the subshell syntax only when you have to:
- 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 more computationally efficient to not fork() the Bash process. Bash is slow enough already.
- Use "here string" like
function <<<$var
instead ofecho $var | function
to avoid forking a subshell and pipe - Use file arguments like
awk '...' $file
or input redirection likefunction << $file
instead of a useless use ofcat
- Use built-in Bash Parameter Expansion for variable/string manipulation rather than forking
sed/tr
:- Use
${VAR#prefix}
or${VAR%suffix}
to removeprefix
orsuffix
respectively - Use
${VAR/pattern/string}
to replacepattern
with string
- Use
- 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 follows:
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, buteval {1..$var}
does
- Unfortunately,
for i in {1..10}; do something_with $i done
- Use
export FOOBAR=val
instead ofFOOBAR=val; export FOOBAR
for clarity and simplicity - Use
[[ expr ]]
instead of[ expr ]
- The
[[
test understands regular expression matching with the=~
operator - The easiest way to use it is by putting the expression in a variable and expanding it after the operator without quotes.
- The
- Use
(( expr ))
instead of[ expr ]
orlet expr
when evaluating numerical expressions- This can include mathematical operators like
$((...))
- This uses normal
<=
,>=
,==
comparisons
- This can include mathematical operators like
- Use
$((...))
for arithmetic expressions instead ofexpr ...
- No need for
$
when referencing variable names inside$((...))
$((...))
can handle hex values and math operators
- No need for
- Error checks should prefer the form
[[ check ]] || action
to avoid leaving a dangling "false" on the return stack- Otherwise,
[[ check ]] && action
will leave a dangling "false" on the stack ifcheck
fails and an immediately following return/end of function will return an error
- Otherwise,
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 - Use
sleep 0.1
instead ofusleep 100000
, sinceusleep
is RHEL-specific
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