首页 \ 问答 \ 为什么我的chdir文件句柄在Perl中不起作用？(Why does my chdir to a filehandle not work in Perl?)

为什么我的chdir文件句柄在Perl中不起作用？(Why does my chdir to a filehandle not work in Perl?)

 当我以文件句柄作为参数尝试“chdir”时，“chdir”返回0，并且pwd仍然返回相同的目录。 应该是这样吗？  
 我试过这个，因为在chdir的文档中我发现：  
 
  “在支持fchdir的系统上，可能会传递文件句柄或目录句柄作为参数，在不支持fchdir的系统上，传递句柄会在运行时产生致命错误。”  
 
 稍后给出：  
#!/usr/bin/perl -w
use 5.010;
use strict;
use Cwd;

say cwd();  # /home/mm
open( my $fh, '>', '/home/mm/Documents/foto.jpg' ) or die $!;
say chdir $fh;  # 0
say cwd();  # /home/mm
 
 我认为这可能是chdir到文件的目录 - 但在这里没有DWIM。 

When I try a "chdir" with a filehandle as argument, "chdir" returns 0 and a pwd returns still the same directory. Should that be so? 
I tried this, because in the documentation to chdir I found: 
 
 "On systems that support fchdir, you might pass a file handle or directory handle as argument. On systems that don't support fchdir, passing handles produces a fatal error at run time." 
 
Given later: 
#!/usr/bin/perl -w
use 5.010;
use strict;
use Cwd;

say cwd();  # /home/mm
open( my $fh, '>', '/home/mm/Documents/foto.jpg' ) or die $!;
say chdir $fh;  # 0
say cwd();  # /home/mm
 
I thought that this would maybe chdir to the directory of the file - but no DWIM for me here.

原文：https://stackoverflow.com/questions/1730434

更新时间：2022-05-19 22:05

最满意答案

 他们可能会使用信息提取技术。  
 以下是斯坦福大学SUST工具的演示：  
 http://nlp.stanford.edu:8080/sutime/process  
 您将在文档中提取关于n-gram（连续词）的属性：  
 
  numberOfLetters  
  numberOfSymbols  
  长度  
  previousWord  
  nextWord  
  nextWordNumberOfSymbols 
 ...  
 
 然后使用分类算法，并提供正，负的例子：  
Observation  nLetters  nSymbols  length  prevWord  nextWord isPartOfDate  
"Feb."       3         1         4       "Wed"     "29th"   TRUE  
"DEC"        3         0         3       "company" "went"   FALSE  
...
 
 你可能会有50个例子，但越多越好。 然后，该算法基于这些示例学习，并且可以应用于以前未见过的未来示例。  
 它可能会学习诸如  
 
  如果以前的单词只是字符，也可能是...  
  现在的词是“二月”，“马尔”，“...”  
  下一个单词在“第十二”，any_number ...  
  那么是日期  
 
 这是Google工程师就此题材播放的体面视频 

They likely use Information Extraction techniques for this. 
Here is a demo of Stanford's SUTime tool: 
http://nlp.stanford.edu:8080/sutime/process 
You would extract attributes about n-grams (consecutive words) in a document: 
 
 numberOfLetters 
 numberOfSymbols 
 length 
 previousWord 
 nextWord 
 nextWordNumberOfSymbols
 ... 
 
And then use a classification algorithm, and feed it positive and negative examples: 
Observation  nLetters  nSymbols  length  prevWord  nextWord isPartOfDate  
"Feb."       3         1         4       "Wed"     "29th"   TRUE  
"DEC"        3         0         3       "company" "went"   FALSE  
...
 
You might get away with 50 examples of each, but the more the merrier. Then, the algorithm learns based on those examples, and can apply to future examples that it hasn't seen before. 
It might learn rules such as  
 
 if previous word is only characters and maybe periods... 
 and current word is in "february", "mar.", "the" ... 
 and next word is in "twelfth", any_number ... 
 then is date 
 
Here is a decent video by a Google engineer on the subject

为什么我的chdir文件句柄在Perl中不起作用？(Why does my chdir to a filehandle not work in Perl?)

最满意答案

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