perl脚本的限制效果

Question

我想在tex文档上运行perl脚本，但不想在序言上运行。如何将它的效果限制在某个模式下的文件部分(例如^\\begin\{document\}$)？这是一个脚本：

# Insert the macro \gr{} around Greek passages.

#!/usr/bin/env perl
use strict;
use warnings;
use Encode;

my $L = qr/[^A-Za-z]/;
my $g = qr/\p{Greek}/;

local $/;           # slurp
$_ = decode('utf-8', <>);

# Remove already existing instances.
s/\\gr
(               # 1
 {
  (             # 2
   (?: \\.          # 3. escaped chars
     | [^{}]
     | (?1)         # recur to 1
   )*
  )  
 }
)
/$2/xg;

# Insert new.
s/(
  [([]*             # begin with puncuation?
  $g                # Greek;
  ($L|\\\w+)*       # contain any non-Latin char or cmd;
  $g                # end with Greek
  [)\]]*            # and puncuation?
  )
/\\gr{$&}/xg;

print encode('utf-8', $_);

Answer 1

local $/可以用于其他东西，而不是完全的静音。$/是输入记录分隔符，perl读取输入记录分隔符的所有内容，并包括输入记录分隔符，然后将其作为一行返回。$/的默认值是换行符( "\n" )。

如果将输入记录分隔符设置为undef，那么perl将永远不会在文件中找到输入记录分隔符，因此您将获得作为一行返回的整个文件。但您可以将输入记录分隔符设置为任何您想要的..。

$ cat data.txt
I don't want to proccess 
this part of the file.
\begin{document}
I just want to process
the stuff down here.
\begin{document}
hello

use strict;
use warnings; 
use 5.020;
use autodie;
use Data::Dumper;

my $fname = 'data.txt';
open my $INFILE, '<', $fname;

my ($unprocessed, $needs_processing);

{
    local $/ = "\\begin{document}\n";
    $unprocessed = <$INFILE>;
    $/ = undef;  #Read rest of file no matter what it contains.
    $needs_processing = <$INFILE>;
}

close $INFILE;

print $unprocessed;
say '-' x 10;
print $needs_processing;

--output:--
I don't want to proccess 
this part of the file.
\begin{document}
----------
I just want to process
the stuff down here.
\begin{document}
hello

如果要对文件进行内部编辑：

use strict;
use warnings; 
use 5.020;
use autodie;
use Data::Dumper;

my $fname = 'data.txt';
my $divider = "\\begin{document}\n";
my $backup = '.bak';

open my $INFILE, '<', $fname;

{
    local ($^I, $/, @ARGV) = ($backup, $divider, $fname);

    CHUNK:
    while(<>) {

        if($. == 1) {    # $. is the line number (starts at 1)
            print;       #STDOUT has been redirected to the file 'data.txt'.
            $/ = undef;  #Read rest of file no matter what it contains.
            next CHUNK;
        }

        #Process $_ here:
        s/e/E/g;

        print;  #STDOUT has been redirected to the file 'data.txt'.
    }

}

close $INFILE;

$ cat data.txt
I don't want to proccess 
this part of the file.
\begin{document}
I just want to procEss
thE stuff down hErE.
\bEgin{documEnt}
hEllo

原始文件将在data.txt.bak中。如果不需要备份，请将一个空字符串分配给$^I。

注意，在您的代码中，语句：

local $/;

没有什么有用的东西。在您的代码中，该语句不在块内(=被大括号包围的部分代码)。local $/说：

1. 将$/的原始值保存在某个地方。
2. 将undef分配给$/。
3. 当包含local $/的块退出时，将原始值赋值给$/。

但是，由于local $/;不在代码中的一个块中，所以不会退出任何块，并且永远不会恢复$/的原始值。因此，没有必要保存$/的原始值。