仅当当前行中存在字符串时才替换 [英] Replace only if string exists in current line

问题描述

我有一行，例如:

sed -i 's/mystring/newstring/' $target

此命令会将所有mystring更改为newstring.

This command will change all mystring to newstring.

我现在想要的是:当程序看到mystring时，如何检查字符串searchstring是否存在的当前行?如果存在，则newstring是1;否则，newstring是0.

What I want now is: when the program sees mystring, how can I check for the current line if the string searchstring exists or not? If it exists, newstring is 1; otherwise, newstring is 0.

推荐答案

解决方案

假设您的输入文件$ target包含以下内容:

Solution

Assuming your input file $target contains the following:

some text mystring some other text
some text mystring a searchstring
just some more text

此命令:

sed -i -e '/searchstring/ s/mystring/1/ ; /searchstring/! s/mystring/0/' $target

会将其内容更改为:

some text 0 some other text
some text 1 a searchstring
just some more text

说明

该脚本包含两个用分号分隔的替代( s )命令.

替代命令接受一个可选的地址范围，该范围选择应进行替代的行.

The substitute command accepts an optional address range that select which lines the substitution should take place.

在这种情况下， regexp 地址用于为第一个命令选择包含 searchstring 的行；以及第二行中不包含 searchstring (注意正则表达式匹配后的感叹号)的行.

In this case regexp address was used to select lines containing the searchstring for the first command; and the lines that do not contain the searchstring (note the exclamation mark after the regexp negating the match) for the second one.

此命令将更好地执行并产生相同的结果:

This command will perform better and produce just the same result:

sed -i -e '/searchstring/ s/mystring/1/ ; s/mystring/0/' $target

重点是命令是按顺序执行的，因此，如果在第一条命令完成后，当前行中的 mystring 子字符串仍然存在，则没有肯定是其中的搜索字符串.

The point is that commands are executed sequentially and thus if there is still a mystring substring in the current line after the first command finished then there is no searchstring in it for sure.

对user946850表示敬意.

Kudos to user946850.

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