String 为什么我不能打印很长的字符串？

我正在编写一个搜索kml文件的Perl脚本，需要打印一行很长的经纬度坐标。以下脚本成功地找到了我要查找的字符串，但只打印了一个空行，而不是字符串的值：

#!/usr/bin/perl
# Strips unsupported tags out of a QGIS-generated kml and writes a new one

$file = $ARGV[0];
# read existing kml file
open( INFO, $file );    # Open the file
@lines = <INFO>;        # Read it into an array
close(INFO);            # Close the file
#print @lines;          # Print the array

$x = 0;
$coord_string = "<coordinates>";
# go through each line looking for above string
foreach $line (@lines) {
    $x++;
    if ( $x > 12 ) {

        if ( $line =~ $coord_string ) {
            $thisCooordString = $line;
            $var_startX       = $x;
            print "Found coord string: $thisCoordString\n";
            print "           on line: $var_startX\n";
        }
    }
}

---

Perl中字符串的最大长度是否有上限？此文件中最长的行约为151000个字符。我已验证文件中的所有行都已成功读取。

您将变量名“两个os”与“三个os”拼写错误：

在脚本中添加use strict和use warnings以防止此类错误。

始终在每个perl脚本中包含和

如果您这样做了，您会收到以下错误消息，提示您出现错误：

Global symbol "$thisCoordString" requires explicit package name

添加这些杂注并简化代码会导致以下结果：

#!/usr/bin/env perl
# Strips unsupported tags out of a QGIS-generated kml and writes a new one

use strict;
use warnings;

local @ARGV = 'HUC8short.kml';

while (<>) {
    if ( $. > 12 && /<coordinates>/ ) {
        print "Found coord string: $_\n";
        print "           on line: $.\n";
    }
}

---

您甚至可以尝试使用perl one行程序，如下所示：

windows命令提示符上的Perl一行程序：

unix提示符上的Perl一行程序：

---

正如其他人所指出的，你需要。不，您必须始终使用和

如果使用strict，则会收到一条错误消息，告诉您变量$thisCoordString或$thisCoordString未使用my声明。使用“警告”会警告您正在打印未定义的字符串

您的整个程序都是用非常古老和过时的Perl编程风格编写的。这是大约二十年前我在Perl 3.0中编写的程序类型。从那时起，Perl发生了很大的变化，使用较新的语法将允许您编写更易于阅读和维护的程序

以下是用更现代的语法编写的基本程序：

#! /usr/bin/env perl
#

use strict;             # Lets you know when you misspell variable names
use warnings;           # Warns of issues (using undefined variables
use feature qw(say);    # Let's you use 'say' instead of 'print' (No \n needed)
use autodie;            # Program automatically dies on bad file operations
use IO::File;           # Lots of nice file activity.

# Make Constants constant
use constant {
    COORD_STRING => qr/<coordinates>/, # qr is a regular expression quoted string
};

my $file = shift;

# read existing kml file
open my $fh, '<', $file;  # Three part open with scalar filehandle

while ( my $line = <$fh> ) {
    chomp $line;        # Always "chomp" on read
    next unless $line =~ COORD_STRING; #Skip non-coord lines
    say "Found coord string: $line";
    say "           on line: " . $fh->input_line_number;
}
close $fh;

许多Perl开发人员都是自学成才的。这并没有什么错，但许多人是从看别人过时的代码、阅读旧的Perl手册或从上世纪90年代从别人那里学习Perl的开发人员那里学习Perl的

---

所以，买一些书来学习新的语法。你可能还想学习一些能引导你学习的东西。引用和OO Perl将允许您编写更长、更复杂的程序。

哎呀，我错过了这一点，真让人尴尬。谢谢。只要将这些行添加到脚本中，您就再也不会犯这种错误了。@MeganMallard在没有严格警告的情况下编写Perl代码是一个非常糟糕的主意，我甚至不会将其推荐给非常熟练的用户，当然也不会推荐给新用户。不使用这些pragmas不会使错误消失，它们只是隐藏起来。

#!/usr/bin/env perl
# Strips unsupported tags out of a QGIS-generated kml and writes a new one

use strict;
use warnings;

local @ARGV = 'HUC8short.kml';

while (<>) {
    if ( $. > 12 && /<coordinates>/ ) {
        print "Found coord string: $_\n";
        print "           on line: $.\n";
    }
}

perl -lne "if($_ =~ /<coordinates>/is && $. > 12) { print \"Found coord string : $_ \n"; print \"  on line : $. \n\";}" HUC8short.kml

perl -lne 'if($_ =~ /<coordinates>/is && $. > 12) { print "Found coord string : $_ \n"; print "  on line : $. \n";}' HUC8short.kml

#! /usr/bin/env perl
#

use strict;             # Lets you know when you misspell variable names
use warnings;           # Warns of issues (using undefined variables
use feature qw(say);    # Let's you use 'say' instead of 'print' (No \n needed)
use autodie;            # Program automatically dies on bad file operations
use IO::File;           # Lots of nice file activity.

# Make Constants constant
use constant {
    COORD_STRING => qr/<coordinates>/, # qr is a regular expression quoted string
};

my $file = shift;

# read existing kml file
open my $fh, '<', $file;  # Three part open with scalar filehandle

while ( my $line = <$fh> ) {
    chomp $line;        # Always "chomp" on read
    next unless $line =~ COORD_STRING; #Skip non-coord lines
    say "Found coord string: $line";
    say "           on line: " . $fh->input_line_number;
}
close $fh;