如何避免heredoc扩展变量？

Question

如何避免heredoc扩展变量？

144

我正在尝试使用环境变量中的替换字符串来创建脚本文件，但我同时也希望防止某些字符被转义。

export PLACEHOLDER1="myPlaceholder1Value"
sudo /bin/su -c "cat << EOF > /etc/init.d/my-script
#!/bin/bash

myvariable_1=toto$PLACEHOLDER1
myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\"
EOF
"

这会导致问题，因为myvariable_final没有被转义并且替换为init脚本依赖项($remote_fs, $syslog, $network, $time)中的变量。

#!/bin/bash

myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=,"

如果我试图在美元符号$后面放一个反斜杠\，我可以避免替换，但是我会得到一个不想要的反斜杠\：

export PLACEHOLDER1="myPlaceholder1Value"
export PLACEHOLDER2="myPlaceholder2Value"
sudo /bin/su -c "cat << EOF > /etc/init.d/my-script
#!/bin/bash

myvariable_1=toto$PLACEHOLDER1
myvariable_2=titi$PLACEHOLDER2
myvariable_final=\"dynamicvar=\$\{myvariable_1},\$\{myvariable_2}\"
EOF
"

导致结果为：

#!/bin/bash

myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=$\{myvariable_1},$\{myvariable_2}"

期望/实际结果应该是:

#!/bin/bash

myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=${myvariable_1},${myvariable_2}"

通过将 EOF 引用在引号中，并在需要时使用反斜杠来控制转义，解决了问题。

export PLACEHOLDER1="myPlaceholder1Value"
export PLACEHOLDER2="myPlaceholder2Value"
sudo /bin/su -c "cat << 'EOF' > /etc/init.d/my-script
#!/bin/bash

myvariable_1=toto$PLACEHOLDER1
myvariable_2=titi$PLACEHOLDER2
myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\"
EOF
"

- TheCodeKiller

7

请注意，只有第一个“EOF”需要加引号！ - masterxilo

1

如果您在引号中使用“EOF”，它将不会被替换。但是，例如在我的情况下，我需要一些变量被替换，而一些环境变量不需要转义。我们该如何做到这一点？ - indianwebdevil

我投票重新开放这个问题，因为该问题并未涵盖其他用户案例：无论如何，请在此处查看：https://github.com/roboll/helmfile/issues/1640#issuecomment-1454786173 - Abdennour TOUMI

2个回答

6

在使用su命令时，请将命令本身放在单引号中，并用反斜杠转义$符号。占位符变量必须在命令bash上下文中设置（在su之后）。因此，您需要执行类似以下的操作：

su -c 'ph="ph"; cat << EOF > script 
varinscript=$ph
var=\${var}
EOF'

- Marc Bredt

你的答案很好，但我想要避免再次将所有的env/export VAR放回命令中。 - TheCodeKiller

那么在这种情况下不需要引用EOF吗？ - Walid

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原文链接

- fedorqui · Accepted Answer

只需使用'EOF'来防止变量扩展：

sudo /bin/su -c "cat << 'EOF' > /etc/init.d/my-script
#                       ^   ^
... contents go here
EOF

来自man bash：

Here Documents

This type of redirection instructs the shell to read input from the current source until a line containing only delimiter (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command.

The format of here-documents is:
      <<[-]word
              here-document
      delimiter
No parameter expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and `.