用 Bash 变量替换 sed
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sed substitution with Bash variables
提问by csta
I am trying to change the values in a text file using sed in a Bash script with the line,
我正在尝试使用 Bash 脚本中的 sed 更改文本文件中的值，
sed 's/draw($prev_number;n_)/draw($number;n_)/g' file.txt > tmp
This will be in a forloop. Why is it not working?
这将是一个for循环。为什么它不起作用？
回答by k.parnell
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:
里面的变量'不会在 Bash 中被替换。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：
$ # 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/'"$a"'/g'
sed: -e expression #1, char 9: unterminated `s' command
Further Reading:
进一步阅读：
- Difference between single and double quotes in Bash*
- Is it possible to escape regex metacharacters reliably with sed
- Using different delimiters for sed substitute command
- Unless you need it in a different file you can use the -i flag to change the file in place
- Bash中单引号和双引号的区别*
- 是否可以使用 sed 可靠地转义正则表达式元字符
- 为 sed 替代命令使用不同的分隔符
- 除非您在不同的文件中需要它，否则您可以使用-i 标志来更改文件
回答by Paul Creasey
Variables within single quotes are not expanded, but within double quotes they are. Use double quotes in this case.
单引号内的变量不会扩展，但双引号内的变量会扩展。在这种情况下使用双引号。
sed "s/draw($prev_number;n_)/draw($number;n_)/g" file.txt > tmp
You could also make it work with eval, but don't do that!!
你也可以让它与 一起工作eval，但不要那样做！！
回答by Kent
This may help:
这可能有帮助：
sed "s/draw($prev_number;n_)/draw($number;n_)/g"
回答by daemonsl
You can use variables like below. Like here, I wanted to replace hostnamei.e., a system variable in the file. I am looking for string look.meand replacing that whole line with look.me=<system_name>
您可以使用如下变量。就像这里，我想替换hostnameie，文件中的一个系统变量。我正在寻找字符串look.me并将整行替换为look.me=<system_name>
sed -i "s/.*look.me.*/look.me=`hostname`/"
You can also store your system value in another variable and can use that variable for substitution.
您还可以将系统值存储在另一个变量中，并可以使用该变量进行替换。
host_var=`hostname`
host_var=`主机名`
sed -i "s/.*look.me.*/look.me=$host_var/"
sed -i "s/.*look.me.*/look.me=$host_var/"
Input file:
输入文件：
look.me=demonic
Output of file (assuming my system name is prod-cfm-frontend-1-usa-central-1):
文件输出（假设我的系统名称是prod-cfm-frontend-1-usa-central-1）：
look.me=prod-cfm-frontend-1-usa-central-1
