如何避免heredoc扩展变量？ [英] How to avoid heredoc expanding variables?

问题描述

我正在尝试使用ENV中的替换字符串创建一个脚本文件，但也希望避免某些转义。

I'm trying to create a script file using substitution string from ENV but want also to prevent some from escaping

export PLACEHOLDER1="myPlaceholder1Value"
export PLACEHOLDER2="myPlaceholder2Value"
sudo /bin/su -c "cat << EOF > /etc/init.d/my-script
#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:    \$remote_fs \$syslog
# Required-Stop:     \$remote_fs \$syslog
# Should-Start:      \$network \$time
# Should-Stop:       \$network \$time
# Default-Start:     2 3 4 5 
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=toto$PLACEHOLDER1
myvariable_2=titi$PLACEHOLDER2
myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\"
EOF
"

不符合 myvariable_final 的结果不会从init脚本依赖关系（$ remote_fs，$ syslog，$ network，$ time）替换为

It results in which is not good as the myvariable_final are not escaped and substituted as the one from the init script dependencies ($remote_fs, $syslog, $network, $time)

#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:
# Required-Stop:
# Should-Start:
# Should-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=,"

< hr>

如果我尝试在美元 $ \ c>，我设法避免替换，但是我收到不需要的反斜杠 \ ：

export PLACEHOLDER1="myPlaceholder1Value"
export PLACEHOLDER2="myPlaceholder2Value"
sudo /bin/su -c "cat << EOF > /etc/init.d/my-script
#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:    \$\remote_fs \$\syslog
# Required-Stop:     \$remote_fs \$syslog
# Should-Start:      \$network \$time
# Should-Stop:       \$network \$time
# Default-Start:     2 3 4 5 
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=toto$PLACEHOLDER1
myvariable_2=titi$PLACEHOLDER2
myvariable_final=\"dynamicvar=\$\{myvariable_1},\$\{myvariable_2}\"
EOF
"

结果：

#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:    $\remote_fs $\syslog
# Required-Stop:
# Should-Start:
# Should-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=$\{myvariable_1},$\{myvariable_2}"

---

想要/参加的结果应该是：

---

Wanted/attended result whould have been :

#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Should-Start:      $network $time
# Should-Stop:       $network $time
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=totomyPlaceholder1Value
myvariable_2=titimyPlaceholder2Value
myvariable_final="dynamicvar=${myvariable_1},${myvariable_2}"

通过以下方式引用 EOF 反斜杠来控制需要时的转义

solved by putting quote around the EOF as below and using backslash to control the escaping when needed

export PLACEHOLDER1="myPlaceholder1Value"
export PLACEHOLDER2="myPlaceholder2Value"
sudo /bin/su -c "cat << 'EOF' > /etc/init.d/my-script
#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          my-script
# Required-Start:    \$remote_fs \$syslog
# Required-Stop:     \$remote_fs \$syslog
# Should-Start:      \$network \$time
# Should-Stop:       \$network \$time
# Default-Start:     2 3 4 5 
# Default-Stop:      0 1 6
# Short-Description: blabla
# Description:       bla bla desc
#
### END INIT INFO
#
myvariable_1=toto$PLACEHOLDER1
myvariable_2=titi$PLACEHOLDER2
myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\"
EOF
"

推荐答案

只需使用'EOF'来防止变量展开：

Just use 'EOF' to prevent the variable from expanding:

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

从 man bash ：

这里Documents

这种类型的重定向指示外壳程序从
当前源读取输入，直到看到只包含分隔符（没有
尾部空白）的行。读取到这一点的所有行都是
，然后用作命令的标准输入。

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.

这里的文档格式为：

      <<[-]word
              here-document
      delimiter

没有参数扩展，命令替换，算术扩展，
或路径名扩展在单词上执行。如果引用单词
中的任何字符，则分隔符是字词上的引号删除的结果，并且
不扩展本文档中的行。 如果word
未引用，则本文档的所有行都将受到参数
扩展，命令替换和算术扩展的影响。在
的后一种情况下，字符序列\被忽略，并且\
必须用于引用字符\，$和`。

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 \ is ignored, and \ must be used to quote the characters \, $, and `.

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