Linux 带有正则表达式的 Bash 子字符串
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Bash substring with regular expression
提问by Luis Andrés García
In a bash script, I′d like to extract a variablestring from a given string. I mean, i′d like to extract the string file.txtfrom the string:
在 bash 脚本中，我想从给定的字符串中提取一个变量字符串。我的意思是，我想file.txt从字符串中提取字符串：
This is the file.txt from my folder.
I tried:
我试过：
var=$(echo "This is the file.txt from my folder.")
var=echo ${var##'This'}
...
but I′d like to make it in a cleaner way, using the expr, sedor awkcommands.
但我想以更简洁的方式使用expr,sed或awk命令。
Thanks
谢谢
Edited:
编辑：
I found another way (nevertheless, the answer with the sed command is the best one for me):
我找到了另一种方法（尽管如此， sed 命令的答案对我来说是最好的）：
var=$(echo 'This is the file.txt from my folder.')
front=$(echo 'This is the ')
back=$(echo ' from my folder.')
var=${var##$front}
var=${var%$back}
echo $var
采纳答案by Daniel S.
The following solution uses sedwith s/(substitution) to remove the leading and trailing parts:
以下解决方案使用sedwith s/(substitution) 删除前导和尾随部分：
echo "This is the file.txt from my folder." | sed "s/^This is the \(.*\) from my folder.$//"
Output:
输出：
file.txt
The \(and \)enclose the part which we want to keep. This is called a group. Because it's the first (and only) group which we use in this expression, it's group 1. We later reference this group inside of the replacement string with \1.
在\(和\)包围，我们要保留的部分。这称为组。因为它是我们在这个表达式中使用的第一个（也是唯一一个）组，所以它是组 1。我们稍后在替换字符串中使用\1.
The ^and $signs make sure that the complete string is matched. This is only necessary for the special case that the filename contains either "from my folder."or "This is the".
在^和$体征确保整个字符串匹配。这仅适用于文件名包含"from my folder."或的特殊情况"This is the"。
回答by EverythingRightPlace
You could try grep:
你可以试试grep：
var=$(egrep -o file.txt)
回答by Dániel
If 'file.txt' is a fixed string, and won't change, then you can do it like this:
如果 'file.txt' 是一个固定字符串，并且不会改变，那么你可以这样做：
var="This is the file.txt from my folder"
var="This is the file.txt from my folder"
Notice that you don't need to echo the string to the variable, you just type it on the right side of the binary '=' operator.
请注意，您不需要将字符串回显到变量中，只需在二进制“=”运算符的右侧键入它即可。
echo $var |sed -e 's/^.*\(file\.txt\).*$/\1/'
echo $var |sed -e 's/^.*\(file\.txt\).*$/\1/'
Depending on your sed(1) version, you can loose the escaping of the parenthesis if you have the -r (extended regexp) option in sed(1).
根据您的 sed(1) 版本，如果您在 sed(1) 中有 -r（扩展正则表达式）选项，则可以取消括号的转义。
If 'file.txt' changes, than you can create a pattern on a best effort basis, like:
如果 'file.txt' 更改，那么您可以尽最大努力创建一个模式，例如：
echo $var |sed -e 's/^.* \([^ ]\+\.[^ ]\+\) .*$/\1/'
echo $var |sed -e 's/^.* \([^ ]\+\.[^ ]\+\) .*$/\1/'
