从多行here文档阅读Bash的变量 [英] Reading a Bash variable from a multiline Here Document

问题描述

什么是的完美的方式从一个猛砸这里读文件为多变量？

看我做这件事的方式如何返回的副作用 1 为 $？ ..

---

猛砸code：

 ＃！/斌/庆典printf的注销... \\ N
未设置变量
printf的退出状态：％S \\ n$？
printf的变量：％S \\ n$ {}变量printf的\\ nprintf的设置为'富'... \\ N
变量='富'
printf的退出状态：％S \\ n$？
printf的变量：％S \\ n$ {}变量printf的\\ nprintf的从进程替换读取标准输入设置为'巴'... \\ n
读变量＆LT; ≤（回声'巴'）
printf的退出状态：％S \\ n$？
printf的变量：％S \\ n$ {}变量printf的\\ nprintf的通过阅读从标准输入字符串在这里... \\ N为'巴兹'
here_string ='巴兹'
阅读变量和LT;＆LT;＆LT; $ {} here_string
printf的退出状态：％S \\ n$？
printf的变量：％S \\ n$ {}变量printf的\\ nprintf的通过阅读从标准输入文件在这里... \\ N为'QUUX'
阅读变量和LT;＆LT;  - EOF
QUUX
EOF
printf的退出状态：％S \\ n$？
printf的变量：％S \\ n$ {}变量printf的\\ nprintf的设置为轰的一声＆LT;＆换行符GT;砰'从这里阅读文档标准输入... \\ n
阅读-d''变量＆LT;＆LT;  - EOF
轰的一声
轰的一声
EOF
printf的退出状态：％S \\ n$？ ＃ONE？！一！oneone？ :)
printf的变量：％S \\ n$ {}变量
 

---

输出

 取消设置...
退出状态：0。
变量：设置为'富'...
退出状态：0。
变量：foo中。设置为'巴'从进程替换读取标准输入...
退出状态：0。
变量：酒吧。设置为巴兹从这里串读标准输入...
退出状态：0。
变量：巴兹。设置为QUUX从这里文档阅读标准输入...
退出状态：0。
变量：QUUX。设置为轰的一声＆LT;＆换行符GT;轰的一声'从这里读取标准输入
文件...
退出状态：1。
变量：轰的一声
轰的一声。
 

解决方案

读返回1​​，当它到达EOF，在同一时间分配看最后的结果。这就是为什么不以换行符结尾的文件是有问题的，因为一个简单的循环读将不会运行的最后一行的循环体。

当您使用读-d''没有把一个NULL字节到输入，这就好比读取文件的最后一行。问题是，为什么你会永远想读在这种情况下，返回0？它这样做就像它应该的。还要注意的是here文档（和herestrings）总是一个换行符添加到自动结束。

有些关联：

• 我的文本文件被破坏！他们缺乏最终的换行符！


• 也许下一个问题你必须： HTTP ：//lists.gnu.org/archive/html/bug-bash/2011-11/msg00148.html

What is the perfect way to read a multiline variable from a Here Document in Bash?

Look at how my way of doing it has the side-effect of returning 1 as $?...

---

Bash code:

#!/bin/bash

printf "Unsetting...\n"
unset variable
printf "Exit status: %s.\n" "$?"
printf "Variable: %s.\n" "${variable}"

printf "\n"

printf "Setting to 'foo'...\n"
variable='foo'
printf "Exit status: %s.\n" "$?"
printf "Variable: %s.\n" "${variable}"

printf "\n"

printf "Setting to 'bar' by reading stdin from process substitution...\n"
read variable < <(echo 'bar')
printf "Exit status: %s.\n" "$?"
printf "Variable: %s.\n" "${variable}"

printf "\n"

printf "Setting to 'baz' by reading stdin from Here String...\n"
here_string='baz'
read variable <<< "${here_string}"
printf "Exit status: %s.\n" "$?"
printf "Variable: %s.\n" "${variable}"

printf "\n"

printf "Setting to 'quux' by reading stdin from Here Document...\n"
read variable <<- 'EOF'
quux
EOF
printf "Exit status: %s.\n" "$?"
printf "Variable: %s.\n" "${variable}"

printf "\n"

printf "Setting to 'thud <newline> thud' by reading stdin from Here Document...\n"
read -d '' variable <<- 'EOF'
thud
thud
EOF
printf "Exit status: %s.\n" "$?" # ONE?!one!!oneone? :)
printf "Variable: %s.\n" "${variable}"

---

Output

Unsetting...
Exit status: 0.
Variable: .

Setting to 'foo'...
Exit status: 0.
Variable: foo.

Setting to 'bar' by reading stdin from process substitution...
Exit status: 0.
Variable: bar.

Setting to 'baz' by reading stdin from Here String...
Exit status: 0.
Variable: baz.

Setting to 'quux' by reading stdin from Here Document...
Exit status: 0.
Variable: quux.

Setting to 'thud <newline> thud' by reading stdin from Here
Document...
Exit status: 1.
Variable: thud
thud.

解决方案

read returns 1 when it reaches EOF, at the same time as assigning the last result read. This is why files that don't end with a newline are problematic, because a simple loop with read will not run the loop body for the final line.

When you use read -d '' without putting a NUL byte into the input, this is just like reading the last line of a file. The question is why would you ever want read to return 0 in this case? It's doing just like it should. Also note that heredocs (and herestrings) always add a newline to the end automatically.

Somewhat related:

• My text files are broken! They lack their final newlines!
• Probably the next question you'll have: http://lists.gnu.org/archive/html/bug-bash/2011-11/msg00148.html

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