perl - 有没有办法在 perl 中本地更改输入记录分隔符？

Question

通过 my $x 将变量 $x 的范围限制为特定的代码块或子例程，将编码人员从“全局变量”的世界中拯救出来"-引起困惑。

但是当涉及到输入记录分隔符$/，显然它的范围是无法限制的。我说的对吗？

因此，如果我忘记在循环结束时或在子例程内重置输入记录分隔符，则我对子例程的调用下面的代码可能会产生意想不到的结果。以下示例演示了这一点。

#!/usr/bin/perl
use strict; use warnings;
my $count_records; my $infile = $ARGV[0]; my $HANDLEinfile;

open $HANDLEinfile, '<', $infile or die "cannot open $infile for reading";
$count_records = 0;
while(<$HANDLEinfile>)
{
    $count_records++; 
    print "$count_records:\n";
    print;
}
close $HANDLEinfile;

look_through_other_file();

print "\nNOW, after invoking look_through_other_file:\n";
open $HANDLEinfile, '<', $infile or die "cannot open $infile for reading";
$count_records = 0;
while(<$HANDLEinfile>)
{
    $count_records++; 
    print "$count_records:\n";
    print;
}
close $HANDLEinfile;

sub look_through_other_file
{
    $/ = undef;
    # here, look through some other file with a while loop
    return;
}

这是它在输入文件上的行为方式:

> z.pl junk
1:
All work
2:
and
3:
no play
4:
makes Jack a dull boy.

NOW, after invoking look_through_other_file:
1:
All work
and
no play
makes Jack a dull boy.
> 

请注意，如果有人尝试更改为

my $/ = undef;

在子程序内部，这会产生错误。

顺便提一下，stackoverflow的标签中，为什么没有“输入记录分隔符”的标签？

Answer 1

my $/= undef; 问题的答案是将其更改为 local $/= undef;。那么修改后的代码如下。

#!/usr/bin/perl
use strict; use warnings;
my $count_records; my $infile = $ARGV[0]; my $HANDLEinfile;

open $HANDLEinfile, '<', $infile or die "cannot open $infile for reading";
$count_records = 0;
while(<$HANDLEinfile>)
{
    $count_records++; 
    print "$count_records:\n";
    print;
}
close $HANDLEinfile;

look_through_other_file();

print "\nNOW, after invoking look_through_other_file:\n";
open $HANDLEinfile, '<', $infile or die "cannot open $infile for reading";
$count_records = 0;
while(<$HANDLEinfile>)
{
    $count_records++; 
    print "$count_records:\n";
    print;
}
close $HANDLEinfile;

sub look_through_other_file
{
    local $/ = undef;
    # here, look through some other file with a while loop
    return;
}

那么就不需要手动将输入记录分隔符返回到另一个值，或者返回到默认值，$/= "\n";。