用 Bash 变量替换 sed [英] sed substitution with Bash variables

问题描述

我正在尝试使用 Bash 脚本中的 sed 更改文本文件中的值，

I am trying to change the values in a text file using sed in a Bash script with the line,

sed 's/draw($prev_number;n_)/draw($number;n_)/g' file.txt > tmp

这将在 for 循环中.为什么它不起作用?

This will be in a for loop. Why is it not working?

推荐答案

' 中的变量在 Bash 中不会被替换.要获得字符串替换(或插值，如果您熟悉 Perl)，您需要将其更改为使用双引号 " 而不是单引号:

Variables inside ' don't get substituted in Bash. To get string substitution (or interpolation, if you're familiar with Perl) you would need to change it to use double quotes " instead of the single quotes:

# Enclose the entire expression in double quotes
$ sed "s/draw($prev_number;n_)/draw($number;n_)/g" file.txt > tmp

# Or, concatenate strings with only variables inside double quotes
# This would restrict expansion to the relevant portion
# and prevent accidental expansion for !, backticks, etc.
$ sed 's/draw('"$prev_number"';n_)/draw('"$number"';n_)/g' file.txt > tmp

# A variable cannot contain arbitrary characters
# See link in the further reading section for details
$ a='foo
bar'
$ echo 'baz' | sed 's/baz/'"$a"'/g'
sed: -e expression #1, char 9: unterminated `s' command

进一步阅读:

• Bash 中单引号和双引号的区别
• 是否有可能可靠地转义正则表达式元字符sed
• 为 sed 替代命令使用不同的分隔符
• 除非您在不同的文件中需要它，否则您可以使用 -i 标志来改变文件的位置

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