perl删除行上的@和=

Question

我是perl脚本的新手,我想删除一些可以在一行开头的字符.我想删除的字符是@和/或=

这是一个文件示例:

@word <= Remove @
=word <= Remove =
@=word <= Remove @ AND =
=@word <= Remove = AND @
=@==@=@=@@word <= Remove all the = and @

目前,我使用substr($line, 0, 1, " ") if "@" eq substr($line, 0, 1);但它只删除了第一个@.如何编辑此行以删除所有前导@和=？

Answer 1

用a做这件事substr是一个很大的开销.只需使用正则表达式替换s///.

while (my $line = <DATA>) {
    $line =~ s/^[@=]+//;
    print $line;
}

__DATA__
@word <= Remove @
=word <= Remove =
@=word <= Remove @ AND =
=@word <= Remove = AND @
=@==@=@=@@word <= Remove all the = and @

这里的图案是/^[@=]+/,这意味着字符串的开头_The,然后一个或多个的任一@或=.您可以使用regex101.com获取有关模式的更详细说明.它会删除它们,就像你的问题所说.

输出是:

word <= Remove @
word <= Remove =
word <= Remove @ AND =
word <= Remove = AND @
word <= Remove all the = and @

如果你想用代码替换空格,你需要做一些更复杂的事情.

s/^([@=]+)/" "x length $1/e;

Tanktalus建议的这个解决方案使用了/e修饰符,它允许你将Perl代码放在替换部分中s///.该x操作重复一个字符串ñ倍.我们使用它来替换整个数量@并且=一次(注意+),空字符串重复多次,因为捕获的字符串有字符.

如果您更喜欢没有/e修饰符的解决方案,请继续阅读.

1 while $line =~ s/^(\s*)[@=]/$1 /;

我们捕获()零个或多个空格\s,并且也恰好匹配其中一个@或者=全部锚定到字符串的开头^.然后我们将其替换为$1来自的捕获()和空白.

我们将此替换作为while循环的条件运行,因为我们希望它在每次尝试后重置正则表达式引擎的位置,因为字符串的开头已经改变.该1 while 修正后的语法是写作的只是一小段路:

while ( $line =~ s/^(\s*)[@=]/$1 / ) {
   # do nothing
}

使用与上面相同的程序运行的代码输出是:

 word <= Remove @
 word <= Remove =
  word <= Remove @ AND =
  word <= Remove = AND @
          word <= Remove all the = and @

要了解为什么这样做正在做,请尝试这样做:

while (my $line = <DATA>) {
    print $line;
    print $line while $line =~ s/^(\s*)[@=]/$1 /;
}

你会看到它在循环的每次迭代中是如何重新开始的1 while ....

@word <= Remove @
 word <= Remove @
=word <= Remove =
 word <= Remove =
@=word <= Remove @ AND =
 =word <= Remove @ AND =
  word <= Remove @ AND =
=@word <= Remove = AND @
 @word <= Remove = AND @
  word <= Remove = AND @
=@==@=@=@@word <= Remove all the = and @
 @==@=@=@@word <= Remove all the = and @
  ==@=@=@@word <= Remove all the = and @
   =@=@=@@word <= Remove all the = and @
    @=@=@@word <= Remove all the = and @
     =@=@@word <= Remove all the = and @
      @=@@word <= Remove all the = and @
       =@@word <= Remove all the = and @
        @@word <= Remove all the = and @
         @word <= Remove all the = and @
          word <= Remove all the = and @