reload_flag=""
if [[ -n "${DEBUG}" ]]; then
reload_flag="--reload"
fi
if [[ -n "${WORKER_COUNT}" ]]; then
workers=${WORKER_COUNT}
else
workers=2
fi
gunicorn --workers ${workers} \
--bind 0.0.0.0:8000 \
${reload_flag} main.wsgi
Писали такие конструкции чтобы проверить наличие флага и сформировать команду правильно?
На самом деле можно сделать тоже самое проще. Для этого используются операторы условной подстановки, доступные в оболочках семейства POSIX.
:- для установки значений по умолчанию
${WORKER_COUNT:-2}
Если переменная не объявлена, то будет дефолтное значение 2.
:+ подставляет указанный текст, если переменная не пуста
${DEBUG:+--reload}
Если что-то есть в переменной то распечатается текст после символа +, в противном случае - ничего. Удобно для опциональных флагов, как в нашем примере.
Итого наш скрипт может выглядеть так:
gunicorn --workers ${WORKER_COUNT:-2} \
--bind 0.0.0.0:8000 \
${DEBUG:+--reload} main.wsgi
Есть еще два оператора.
:= не только подставить дефолтное значение, но и присвоить его переменной, если она пуста
# никаких переменных еще нет
VAL1=${VAL2:=hello}
# теперь доступны обе
echo $VAL1 $VAL2
# hello hello
:? остановить выполнение с ошибкой, если переменной нет.
echo ${MISS:?is required}
bash: MISS: is required
Код выхода будет 1.
#tricks#linux
🌎 Glowing deep-sea animals like the comb jellyfish and dragonfish create their own light using bioluminescence. This adaptation helps them hunt, attract mates, or avoid predators in pitch-black ocean depths. Some dragonfish possess "invisible" red bioluminescence, seen only by their own kind, for stealthy communication. ✨
#ocean⚡#animals⚡#bioluminescence
👉subscribe Interesting Planet
👉more Channels
🌍 The Waitomo Glowworm Caves in New Zealand are famous for thousands of tiny insects that light up the darkness, creating a galaxy-like effect in this unique karst underground world. ✨
#caves⚡#karst⚡#bioluminescence⚡#geography⚡#nature⚡#earth
👉subscribe Amazing Geography
👉more Channels
🌎 Shrouded in darkness, the “midnight zone” of the ocean lies below 1,000 meters, where sunlight can’t reach and pressure crushes like a dozen elephants. Creatures here glow with bioluminescence and withstand freezing cold, revealing how life adapts to our planet’s most mysterious depths. ✨
#ocean⚡#bioluminescence⚡#deepsea
👉subscribe Interesting Planet
🌎 Lightning bugs, or fireflies, create their glow through a special enzyme called luciferase. This reaction produces cold light, wasting almost no energy as heat—a marvel of natural engineering for nighttime signaling. ✨
#bioluminescence⚡#insects⚡#nature
👉subscribe Interesting Planet
🌎 Glowing tides known as bioluminescent bays light up in places like Puerto Rico. Microorganisms called dinoflagellates produce blue-green light when stirred by waves or movement. The brightest, Mosquito Bay, can host up to 700,000 glowing organisms in just one liter of water. ✨
#bioluminescence⚡#ocean⚡#phenomenon
👉subscribe Interesting Planet
👉more Channels
🌍 Some coasts shine with glowing “blue waves” at night, caused by tiny plankton called dinoflagellates emitting light when disturbed—a dazzling phenomenon known as marine bioluminescence. ✨
#seas⚡#coastline⚡#bioluminescence⚡#geography⚡#nature⚡#earth
👉subscribe Amazing Geography
👉more Channels
🌎 Glowing waves known as “sea sparkle” can light up coastlines at night. This effect is caused by bioluminescent plankton emitting blue light when disturbed. Some blooms stretch for kilometers and are most often seen in warm coastal waters. ✨
#bioluminescence⚡#ocean⚡#plankton
👉subscribe Interesting Planet
👉more Channels
🌎 Glowing waves sometimes light up the ocean at night thanks to bioluminescent plankton. These tiny marine organisms emit blue light when disturbed, turning shorelines into breathtaking, natural light shows. ✨
#ocean⚡#bioluminescence⚡#plankton
👉subscribe Interesting Planet
🌎 The vampire squid thrives in the ocean’s dark depths by using bioluminescent light organs to confuse predators. Its name comes from its cloak-like webbed arms, not from blood-drinking. ✨
#ocean⚡#cephalopod⚡#bioluminescence
👉subscribe Interesting Planet
🌎 In the Mediterranean Sea, the bearded fireworm boasts bristly, glowing spines that can cause a painful sting. This marine worm’s bioluminescence warns predators while its venomous bristles deter unwelcome touches—a perfect example of nature’s flashy, double-edged defense system. ✨
#fireworm⚡#bioluminescence⚡#ocean
👉subscribe Interesting Planet
🌎 Somewhere in the world’s oceans, the “milky sea” phenomenon can make water glow bright blue for up to several days. Caused by massive colonies of bioluminescent bacteria, these rare glowing patches can cover areas larger than 15,000 square kilometers—visible even from space. ✨
#ocean⚡#mysteries⚡#bioluminescence⚡#bacteria
👉subscribe Interesting Planet