shell 变量设定默认值 ${parameter:-word}

Reference: [ variable assignment in scripts ]


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Script

$echo ${JENKINS_VERSION:-2.7.4}
2.7.4
$JENKINS_VERSION=2.99
$echo ${JENKINS_VERSION:-2.7.4}
2.99

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原文地址：https://www.cnblogs.com/tiantiandas/p/shell_set_default_value_for_unset_variable.html