錯誤捕捉在Perl的正則表達式4個字符單詞

的Learning Perl，男試圖捕捉在用戶給定的文件的4個字符的話，下面是其攜帶regex PATTEN匹配錯誤捕捉在Perl的正則表達式4個字符單詞

代碼段

while(<data>) 
{ 
    $caps_string = $_; #assigning data to variable 
    print "This is default string :\n $caps_string \n\n"; 

    $caps_string =~ tr/a-z/A-Z/; #lower to upper case 
    print "This is caps string :\n $caps_string \n\n"; 

    $caps_string =~ /\b[a-z]{4}\b/ig; #capturing 4 character words - which fails 
    print "4 digit words in string are : \n $caps_string \n\n"; 

}

的 while loop

輸出：

This is default string : 
This is a text file data, coming from input.txt #correct 

This is caps string : 
THIS IS A TEXT FILE DATA, COMING FROM INPUT.TXT #correct 

4 digit words in string are : 
THIS IS A TEXT FILE DATA, COMING FROM INPUT.TXT #incorrect according to me

預期輸出最後一行：

#exact 4 character words 
    THIS TEXT FILE DATA FROM

正則表達式模式和我試圖測試字符串，顯示爲expected on regex101

輸出，怎麼在Perl使用時的模式是錯的，請指導！

來源

2014-03-05 NoobEditor

你可以試試我下面發佈的解決方案 –

在你當前的解決方案中，你需要捕獲一個數組中的所有4個字符的單詞......然後將該數組作爲你的輸出...你在做什麼現在只是匹配模式的輸入..但你沒有存儲任何地方的實際匹配。 –

你需要用()指定正則表達式捕獲：

$caps_string =~ /\b([a-z]{4})\b/ig; # Note the case-insensitive matching with /i

然後你最想存儲的匹配，以及：

my @fours = $caps_string =~ /\b([a-z]{4})\b/ig; # 'THIS', 'TEXT', 'FILE', ... 

print "@fours"; # "THIS TEXT FILE DATA FROM"

來源

2014-03-05 07:10:43 Zaid

不會'$ caps_string =〜/ \ b（[a-z] {4}）\ b/g;'將'$ caps_string'中的單詞匹配存儲爲單個字符串，如'tr'在轉換後存儲問，因爲'tr'正在保存它，所以我在想''正則表達式'也會取代它！ – NoobEditor

@NoobEditor：如果你想修改字符串，請使用's ///' – Zaid

我試過'$ caps_string =〜s/\ b [a-z] {4} \ b/ig /;打印「字符串中的4位數字是：\ n $ caps_string \ n \ n」; 「但我仍然得到全文...心靈再次糾正我？ :) – NoobEditor

#!/usr/local/bin/perl 
$caps_string = 'This is a text file data, coming from input.txt'; 
print "This is default string :\n $caps_string \n\n"; 

$caps_string =~ tr/a-z/A-Z/; #lower to upper case 
print "This is caps string :\n $caps_string \n\n"; 

## You already converted string to upper case 
## So your pattern needs to match upper case letter .. so [A-Z] 
## And then you would want to store all the matches in an array 
@matches = $caps_string =~ /\b[A-Z]{4}\b/g; #capturing 4 character words 
    print "4 digit words in string are : @matches \n";

輸出我得到：

This is default string : 
This is a text file data, coming from input.txt 

This is caps string : 
THIS IS A TEXT FILE DATA, COMING FROM INPUT.TXT 

4 digit words in string are : THIS TEXT FILE DATA FROM

來源

2014-03-05 08:07:03

錯誤捕捉在Perl的正則表達式4個字符單詞

回答

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