TMPDIR 中的“-”是做什么的？
What a '-' in TMPDIR do?
我最近看到一个示例，其中调用命令时传递给 env 的选项如下：
TMPDIR="${TMPDIR:-/tmp}"
$TMPDIR 中的 - 有什么作用？这是针对 linux.
的未指定版本
It sets $TMPDIR to itself if it's set, otherwise it sets it to /tmp.
${parameter:-word}
If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
因此，如果它为空或未设置，则将 TMPDIR 设置为 /tmp。如果省略:（例如${TMPDIR-/tmp}，它只测试变量是否未设置，如指定的：
Omitting the colon results in a test only for a parameter that is unset. Put another way, if the colon is included, the operator tests for both parameter’s existence and that its value is not null; if the colon is omitted, the operator tests only for existence.
我最近看到一个示例，其中调用命令时传递给 env 的选项如下：
TMPDIR="${TMPDIR:-/tmp}"
$TMPDIR 中的 - 有什么作用？这是针对 linux.
It sets $TMPDIR to itself if it's set, otherwise it sets it to /tmp.
${parameter:-word}
If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
因此，如果它为空或未设置，则将 TMPDIR 设置为 /tmp。如果省略:（例如${TMPDIR-/tmp}，它只测试变量是否未设置，如指定的：
Omitting the colon results in a test only for a parameter that is unset. Put another way, if the colon is included, the operator tests for both parameter’s existence and that its value is not null; if the colon is omitted, the operator tests only for existence.