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16+
17+
18+ < p > </ p >
19+ < pre class ="screen ">
20+
21+ [root@localhost tmp]# echo "welcome $HOME ${USER:=a8m}" | envsubst
22+ welcome /root root
23+
24+ </ pre >
25+ < pre class ="screen ">
26+
27+ [root@localhost tmp]# cat config.template
28+ HOME=${HOME}
29+ USER=${USER}
30+
31+ [root@localhost tmp]# envsubst < config.template > config.conf
32+
33+ [root@localhost tmp]# cat config.conf
34+ HOME=/root
35+ USER=root
36+
37+ </ pre >
38+ < p > 只替换 ${USER} 变量</ p >
39+ < pre class ="screen ">
40+
41+ [root@localhost tmp]# envsubst '${USER}' < config.template > config.conf
42+ [root@localhost tmp]# cat config.conf
43+ HOME=${HOME}
44+ USER=root
45+
46+ </ pre >
47+ < p > 模版变量</ p >
48+ < pre class ="screen ">
49+
50+ ${var} var值( 与 $var 相同)
51+ ${var-$DEFAULT} 如果未设置 var，则将表达式计算为 $DEFAULT
52+ ${var:-$DEFAULT} 如果未设置var或者为空，则将表达式计算为 $DEFAULT
53+ ${var=$DEFAULT} 如果未设置 var，则将表达式计算为 $DEFAULT
54+ ${var:=$DEFAULT} 如果未设置var或者为空，则将表达式计算为 $DEFAULT
55+ ${var+$OTHER} 如果为 var，则将表达式计算为 $OTHER,，否则为空字符串
56+ ${var:+$OTHER} 如果为 var，则将表达式计算为 $OTHER,，否则为空字符串
57+
58+ </ pre >
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