正则表达式惰性匹配不匹配贪婪表达式匹配的字符串 [英] Regex lazy matching does not match string matched by greedy expression

问题描述

假设我有以下文本文件（称为 test.txt ）：

  \centerline {\includegraphics [width = 0.50 \columnwidth] {example_graph.pdf}} 
 \centerline {\includegraphics [width = 0.5 \columnwidth] {coarse_grain_illustration.png}} 
 \centerline {\includegraphics [width = 0.8 \columnwidth] {1y26_energy_dists.pdf}} 
  

如果我用贪婪的匹配进行搜索，我会得到我期望的结果：

pre $ [user @ host test] $ grep '\\includegraphics。* df'test.txt
\centerline {\includegraphics [width = 0.50 \columnwidth] {example_graph.pdf}}
\centerline {\includegraphics [ width = 0.8 \columnwidth] {1y26_energy_dists.pdf}}
================================= ================================================== == b



然而，如果我使用懒惰评估，我不会得到任何结果：



  [user @ host test] $ grep'\\includegraphics。*？df'test.txt 
 =================== ================================================== ====================================== 
  

什么给了？为什么使用懒惰评估不匹配本质上相同的模式？

解决方案

。*？或懒惰模式在任何地方都不受支持。你将不得不在Perl模式下使用 grep -P 或grep来实现它。

Suppose I have the following text file (called test.txt):

\centerline{\includegraphics[width=0.50 \columnwidth]{example_graph.pdf}}
\centerline{\includegraphics[width=0.5 \columnwidth]{coarse_grain_illustration.png}}
\centerline{\includegraphics[width= 0.8 \columnwidth]{1y26_energy_dists.pdf}}

If I search with greedy matching, I get the results I expect:

[user@host test]$ grep '\\includegraphics.*df' test.txt
\centerline{\includegraphics[width=0.50 \columnwidth]{example_graph.pdf}}
\centerline{\includegraphics[width= 0.8 \columnwidth]{1y26_energy_dists.pdf}}
===========================================================================================================

If I use lazy evaluation, however, I get no results:

[user@host test]$ grep '\\includegraphics.*?df' test.txt
===========================================================================================================

What gives? Why does using lazy evaluation not match what is essentially the same pattern?

解决方案

.*? or lazy mode is not supported everywhere. You will have to use grep -P or grep in perl mode to achieve it.

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