ksh88将单引号更改为heredocs中的双引号? [英] ksh88 changing single quotes to double quotes inside heredocs?

问题描述

我似乎遇到了一个特定于ksh88的问题，该问题将单引号更改为双引号，但仅在某些涉及Heredocs和命令替换的情况下.

I seem to be running into an issue that's specific to ksh88 that's changing single quotes to double quotes, but only under certain situations involving heredocs and command substitution.

这是一个例子:

#!/bin/ksh

# This example works correctly
echo "Example 1:"
cat <<EOF
The 'quick' brown fox "jumped" over the lazy dog.
EOF
echo


# This example is broken
echo "Example 2:"
var=$(cat <<EOF
The 'quick' brown fox "jumped" over the lazy dog.
EOF)
echo "${var}"
echo


# This example works correctly
echo "Example 3:"
var=`cat <<EOF
The 'quick' brown fox "jumped" over the lazy dog.
EOF`
echo "${var}"
echo

这是输出(请注意示例2的不同之处):

And here's the output (note how Example 2 is different):

Example 1:
The 'quick' brown fox "jumped" over the lazy dog.

Example 2:
The "quick" brown fox "jumped" over the lazy dog.

Example 3:
The 'quick' brown fox "jumped" over the lazy dog.

在命令运行前 似乎发生了'到"的替换.实际上，heredoc正在将SQL传递给Oracle.通过将'更改为"，字符串将转换为标识符，从而破坏了SQL.在执行上述代码期间启用xtrace也可以观察到这一点.

The ' to " substitution seems to occur before the command runs. In actual context, the heredoc is passing SQL to Oracle. By changing ' to ", strings are being converted to identifiers, thus breaking the SQL. This can also be observed by enabling xtrace during execution of the above code.

如何在不使用反引号的情况下阻止上述代码段中的'到"转换?

How can I prevent the ' to " conversion in the above code snippet without using backticks?

情节变浓了.用反引号表示法替换命令替换$( ... )不会用双引号替换单引号.所以(可选)问题二:为什么?

The plot thickens. Replacing the command substituion $( ... ) with backtick notation doesn't replace the single quotes with double quotes. So (optional) question two: why?

推荐答案

几年前，当我发现相同的bug时，这里是我的笔记.

Here are my notes when I discovered this same bug several years ago.

测试脚本:

#!/bin/ksh
cat <<EOF
  $PWD "$PWD" '$PWD'
EOF
echo `cat <<EOF
  $PWD "$PWD" '$PWD'
EOF
`
echo $(cat <<EOF
  $PWD "$PWD" '$PWD'
EOF
)

不同外壳的输出:

• Linux KSH版本M 1993-12-28 q
• Linux Bash 3.00.15(1)

(注意:工作正常)

 /home/jrw32982 "/home/jrw32982" '/home/jrw32982'
 /home/jrw32982 "/home/jrw32982" '/home/jrw32982'
 /home/jrw32982 "/home/jrw32982" '/home/jrw32982'

• AIX版本M-11/16/88f
• Solaris版本M-11/16/88i

(注意:单引号替换为双引号，并且变量不被替换)

(NOTE: single quotes replaced with double quotes and variable not substituted)

 /home/jrw32982 "/home/jrw32982" '/home/jrw32982'
 /home/jrw32982 "/home/jrw32982" '/home/jrw32982'
 /home/jrw32982 "/home/jrw32982" "$PWD"

解决方法:

1. 从此处文件外部计算单引号字符串

1. Compute the single-quoted string externally from the here-file

abc=xyz
STR="'$abc'"
x=$( cat <<EOF
  $abc "$abc" $STR
EOF
)

• 在函数中使用此处文件而不是直接使用

• Use the here-file in a function instead of directly

  fn() {
    cat <<EOF
      $abc "$abc" '$abc'
  EOF
  }
  abc=xyz
  x=$(fn)
  

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