英文:
How to print ENV VAR name to file, NOT VALUE from linux cli
问题
我有这个：
cat > ~/add_api_txt_hook.sh <<EOF
#!/bin/bash
...
echo $MY_ENV_VAR
EOF
当创建此文件时，MY_ENV_VAR未设置。因此它在文件中变成了“”。
我希望文件内容是：
#!/bin/bash
...
echo $MY_ENV_VAR
而不是：
#!/bin/bash
...
echo ""
如何将实际的ENV VAR ***KEY*** 打印到文件中？我在互联网上搜索过，但它只返回如何将值打印到文件中的方法。
尝试了谷歌和各种关于键（），""，{}等的语法...
英文:
I have this:
cat > ~/add_api_txt_hook.sh <<EOF
#!/bin/bash
...
echo $MY_ENV_VAR
EOF
MY_ENV_VAR is not set when this file is made. So it makes it "" in the file.
I want the file contents to be
#!/bin/bash
...
echo $MY_ENV_VAR
NOT:
#!/bin/bash
...
echo ""
How do I print the actual ENV VAR KEY to the file? I have searched the internet, but it only returns how to print the value to the file.
Tried google and various syntax around the key (), "", {} etc...
答案1
得分: 2
有几种方法可以实现这个。显然，正如SiKing指出的那样，你可以用反斜杠转义美元符号。
你也可以引用 EOF 本身。例如：
$: cat >x <<EOF
echo $PATH
EOF
将 $PATH 的值（包括空值，在你的情况下）放入文件中，
$: cat >x <<'EOF'
echo $PATH
EOF
则不会：
$: cat x
echo $PATH
同样，你可以使用“here-string”：
$: cat <<<'echo $PATH'
echo $PATH
但要注意，无论是单引号还是双引号，here-doc 的行为基本相同 -
$: cat <<"EOF"
echo $PATH
EOF
echo $PATH
here-string 有所区别；单引号不会扩展变量，而双引号会。
$: cat <<<"echo $PATH"
echo /c/Users/....（已编辑）
英文:
There are several ways to accomplish this.
Obviously, as SiKing pointed out, you can just backslash-escape the dollar sign.
You can also quote the EOF itself. While
$: cat >x <<EOF
echo $PATH
EOF
puts the value of $PATH (including being empty, as in your case) in the file,
$: cat >x <<'EOF'
echo $PATH
EOF
does not:
$: cat x
echo $PATH
Likewise, you can use a "here-string":
$: cat <<<'echo $PATH'
echo $PATH
But be aware that where a here-doc behaves much the same whether single- or double-quotes are used -
$: cat <<"EOF"
echo $PATH
EOF
echo $PATH
here-strings differentiate; single-quotes don't expand variables, but doubles do.
$: cat <<<"echo $PATH"
echo /c/Users/....(redacted)
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