string bash：将字符串变量解释为文件名/路径
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bash: interpret string variable as file name/path
提问by Keith Wiley
My bash script receives a filename (or relative path) as a string, but must then read from that file. I can only read from a filename if I declare it as a literal directly in the script (without quotes)...which is impossible for arguments since they are implicitly strings to begin with. Observe:
我的 bash 脚本以字符串形式接收文件名（或相对路径），但必须从该文件中读取。如果我直接在脚本中将其声明为文字（不带引号），我只能从文件名中读取……这对于参数来说是不可能的，因为它们是隐式字符串开头。观察：
a="~/test.txt"
#Look for it
if [[ -a $a ]] ; then
echo "A Found it"
else
echo "A Error"
fi
#Try to use it
while read line; do
echo $line
done < $a
b='~/test.txt'
#Look for it
if [[ -a $b ]] ; then
echo "B Found it"
else
echo "B Error"
fi
#Try to use it
while read line; do
echo $line
done < $b
c=~/test.txt
#Look for it
if [[ -a $c ]] ; then
echo "C Found it"
else
echo "C Error"
fi
#Try to use it
while read line; do
echo $line
done < $c
YIELDS:
产量：
A Error
./test.sh: line 10: ~/test.txt: No such file or directory
B Error
./test: line 12: ~/test.txt: No such file or directory
C Found it
Hello
As stated above, I can't pass a command line argument to the routines above since I get the same behavior that I get on the quoted strings.
如上所述，我无法将命令行参数传递给上述例程，因为我得到的行为与我在引用字符串上得到的行为相同。
回答by michaelb958--GoFundMonica
This is part of the rules of ~-expansion. It is clearly stated in the Bash manual that this expansion is not performed when the ~is quoted.
这是~-expansion规则的一部分。Bash 手册中明确指出，~引用时不执行此扩展。
Workaround 1
解决方法 1
Don't quote the ~.
不要引用~.
file=~/path/to/file
If you need to quote the rest of the filename:
如果您需要引用文件名的其余部分：
file=~/"path with spaces/to/file"
(This is perfectly legal in a garden-variety shell.)
（这在花园式贝壳中是完全合法的。）
Workaround 2
解决方法 2
Use $HOMEinstead of ~.
使用$HOME代替~。
file="$HOME/path/to/file"
BTW: Shell variable types
顺便说一句：外壳变量类型
You seem to be a little confused about the types of shell variables.
你似乎对 shell 变量的类型有点困惑。
Everything is a string.
一切都是一个字符串。
Repeat until it sinks in: Everything is a string.(Except integers, but they're mostly hacks on top of strings AFAIK. And arrays, but they're arrays of strings.)
重复直到它沉入水中：一切都是字符串。（除了整数，但它们主要是在字符串 AFAIK 之上的 hack。和数组，但它们是字符串数组。）
This is a shell string: "foo". So is "42". So is 42. So is foo. If you don't need to quote things, it's reasonable not to; who wants to type "ls" "-la" "some/dir"?
这是一个 shell 字符串："foo". 也是"42"。也是42。也是foo。如果你不需要引用东西，不引用是合理的；谁想打字"ls" "-la" "some/dir"？
