-bash: yarn: command not found

> yarn@1.22.17 preinstall /usr/local/Cellar/node/12.5.0/lib/node_modules/yarn
> :; (node ./preinstall.js > /dev/null 2>&1 || true)

/usr/local/Cellar/node/12.5.0/bin/yarnpkg -> /usr/local/Cellar/node/12.5.0/lib/node_modules/yarn/bin/yarn.js
/usr/local/Cellar/node/12.5.0/bin/yarn -> /usr/local/Cellar/node/12.5.0/lib/node_modules/yarn/bin/yarn.js
+ yarn@1.22.17
updated 1 package in 0.724s
gw:~ gw$ /usr/local/Cellar/node/12.5.0/bin/yarn --version
1.22.17
gw:~ gw$ cd /Users/\/react-native-hpjysinglesday 
gw:react-native-hpjysinglesday gw$ yarn
-bash: yarn: command not found-native-hpjysinglesday$ 

解决方案:

/usr/local/Cellar/node/12.5.0/bin/yarn start 

1.yarn安依赖，
2.yarn start:single跑本地调试