从任何类型的标量,我可以使用什么正则表达式来匹配它的前五行并丢弃其余的？
解决方法
奇怪的请求,但这应该这样做：
#!/usr/bin/perl
use strict;
use warnings;
my $s = join '',map { "$_\n" } 1 .. 9;
my ($first) = $s =~ /^((?:.*\n){0,5})/;
my ($last) = $s =~ /((?:.*\n){0,5})$/;
print "first:\n${first}last:\n$last";
一个更常见的解决方案是这样的：
#!/usr/bn/perl
use strict;
use warnings;
#fake a file for the example
my $s = join '',map { "$_\n" } 1 .. 9;
open my $fh,"<",\$s
or die "could not open in memory file: $!";
my @first;
while (my $line = <$fh>) {
push @first,$line;
last if $. == 5;
}
#rewind the file just in case the file has fewer than 10 lines
seek $fh,0;
my @last;
while (my $line = <$fh>) {
push @last,$line;
#remove the earliest line if we have to many
shift @last if @last == 6;
}
print "first:\n",@first,"last:\n",@last;
