This chapter documents the coding style used in live systems.
15.1 CompatibilitÃ
Avoid "bashisms", the codebase must be POSIX compliant and thus universally compatible.
Furthermore it must comply with the version of the POSIX specification chosen by the current Debian Policy.
È possibile verificare i propri script con "sh -n" e "checkbashisms".
Assicurarsi che tutto il codice giri con 'set -e'.
15.2 Rientri
Usare sempre i tab piuttosto che gli spazi.
Keep case branch terminators (";;") aligned with the "content" of the branch, rather than the branch "entry".
Corretto:
case "${1}" in
foo)
foobar
;;
bar)
foobar
;;
esac
15.3 Ritorno a capo
Generally, lines should be 80 chars at maximum.
Placement of keywords like then and do should be chosen with good judgement with respect to clutter and readability. For small bits of code in particular it should be preferred to have them on the same line as the prior keyword they relate to (if; for; etc). Only place on the next line where it makes good sense to do so; typically this might only be to comply with maximum line length restrictions. One situation where they should always be placed on the next line is where what they follow is broken up onto multiple lines, and thus it being on a new line creates clear separation between that and the body of code following it. I.e. :
Preferred:
if foo; then
bar
fi
for FOO in $ITEMS; do
bar
done
if [ "${MY_LOCATION_VARIABLE}" = "something" ] && [ -e "${MY_OUTPUT_FILE}" ]
then
MY_OTHER_VARIABLE="$(some_bin ${FOOBAR} | awk -F_ '{ print $1 }')"
fi
if [ "${MY_FOO}" = "something" ] && [ -e "path/${FILE_1}" ] ||
[ "${MY_BAR}" = "something_else" ] && [ ${ALLOW} = "true" ]
then
foobar
fi
Less ideal:
if [ "${MY_LOCATION_VARIABLE}" = "something" ] && [ -e "${MY_OUTPUT_FILE}" ]; then
MY_OTHER_VARIABLE="$(some_bin ${FOOBAR} | awk -F_ '{ print $1 }')"
fi
Prefer placing the opening brace of a function on a new line (for consistency with established style), and keep the braces aligned with the function name:
Corretto:
Foo ()
{
bar
}
Bad (inconsistent with existing style):
Foo () {
bar
}
Awful:
Foo ()
{
bar
}
15.4 Variabili
Le variabili vanno sempre scritte in maiuscolo.
Config variables used in live-build should start with an LB_ prefix.
Local function variables should be restricted to local scope.
Le variabili in live-config relative ai parametri di avvio iniziano con LIVE_.
Tutte le altre variabili in live-config iniziano con il prefisso _.
Intorno alle variabili utilizzare le graffe; ad esempio scrivere ${FOO} invece di $FOO.
Always protect variables with quotes to respect potential whitespaces (except where necessary to achieve correct word splitting): write "${FOO}" not ${FOO}.
Per coerenza usare sempre le virgolette quando si assegnano valori alle variabili:
Sbagliato:
FOO=bar
Corretto:
FOO="bar"
If multiple variables are used, prefer quoting the full expression:
Typically bad:
if [ -f "${FOO}"/foo/"${BAR}"/bar ]; then
foobar
fi
Corretto:
if [ -f "${FOO}/foo/${BAR}/bar" ]; then
foobar
fi
15.5 Varie
Prefer "|" (without the surround quotes) as a separator in calls to sed, e.g. "sed -e 's|foo|bar|'" (without "").
Don't use the test command for comparisons or tests, use "[" and "]" (without ""); e.g. "if [ -x /bin/foo ]; ..." and not "if test -x /bin/foo; ...".
Use case wherever it makes code more readable than conditional checks (if foo; ... and tests without the actual if keyword, e.g. [ -e "${FILE}" ] || exit 0).
Use "Foo_bar" style names for functions, i.e. a capital first letter, then all lowercase, with sensible use of underscores for better readability.
