Emacs正则表达式：什么\<和\>可以做到吗？ [英] Emacs regular expression: what \< and \> can do that \b cannot do?

问题描述

正则表达式反斜杠 - GNU Emacs手册说 \< 在单词开头匹配， \> 单词和 \b 匹配单词边界。 \b 与其他非Emacs正则表达式一样。但是，对于Emacs正则表达式来说，似乎 \< 和 \> 是特别的。是否需要 \< 和 \> ，而不是 \\ \\b ？例如， \bword\b 将与 \< word\> 将匹配，唯一的区别是后者更可读。

Regexp Backslash - GNU Emacs Manual says that \< matches at the beginning of a word, \> matches at the end of a word, and \b matches a word boundary. \b is just as in other non-Emacs regular expressions. But it seems that \< and \> are particular to Emacs regular expressions. Are there cases where \< and \> are needed instead of \b? For instance, \bword\b would match the same as \<word\> would, and the only difference is that the latter is more readable.

推荐答案

如果您假设他们的行为相同，您可以获得意想不到的结果..

什么可以\<和> \可以做什么？

答案是 \< 和 \> 是显式 ...这个结尾！只有这个目的！

\b 是一般 ....一个单词的末尾都会匹配.. 。

You can get unexpected results if you assume they behave the same..
What can \< and > that \b can do?
The answer is that \< and\> are explicit... This end of a word! and only this end!
\bis general.... Either end of a word will match...

GNU运算符* Word Operators

line="cat dog sky"  
echo "$line" |sed -n "s/\(.*\)\b\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\>\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\<\(.*\)/# |\1|\2|/p"
echo
line="cat  dog  sky"  
echo "$line" |sed -n "s/\(.*\)\b\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\>\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\<\(.*\)/# |\1|\2|/p"
echo
line="cat  dog  sky  "  
echo "$line" |sed -n "s/\(.*\)\b\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\>\(.*\)/# |\1|\2|/p"
echo "$line" |sed -n "s/\(.*\)\<\(.*\)/# |\1|\2|/p"
echo

输出

# |cat dog |sky|
# |cat dog| sky|
# |cat dog |sky|

# |cat  dog  |sky|
# |cat  dog|  sky|
# |cat  dog  |sky|

# |cat  dog  sky|  |
# |cat  dog  sky|  |
# |cat  dog  |sky  |

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