在Perl哈希中使用未初始化的值

Question

我有一个脚本可以解析df到perl可以使用的东西.

 1 #!/usr/bin/perl
 2 use strict;
 3 use warnings;
 4
 5 my @headers = qw(name size used free capacity mount);
 6 my @df = `df -k`;
 7 shift @df;  # get rid of the header
 8
 9 my %devices;
10 for my $line (@df) {
11     my %info;
12     @info{@headers} = split /\s+/, $line;  # note the hash slice
13     $info{capacity} = _percentage_to_decimal($info{capacity});
14     $devices{ $info{mount} } = \%info;
15 }
16
17 # Change 12.3% to .123
18 sub _percentage_to_decimal {
19     my $percentage = shift;
20     $percentage =~ s{%}{};
21     return $percentage / 100;
22 }
23 # Now the information for each device is in a hash of hashes.
24
25 # Show how much space is free in device /dev/ad4s1e
26 print $devices{"/production/log"}{free} ;
27 print "\n";
28 for my $info (values %devices) {
29     # Skip to the next device if its capacity is not over 60%.
30     next unless $info->{capacity} > .10;
31
32     # Print some info about each device
33     printf "%s is at %d%% with %dK remaining.\n",
34         $info->{mount}, $info->{capacity}*100, $info->{free};
35 }

但是我一直收到这些警告.

Use of uninitialized value in substitution (s///) at ./get_df line 21.
Use of uninitialized value in division (/) at ./get_df line 22.
Use of uninitialized value in hash element at ./get_df line 15.
Use of uninitialized value in substitution (s///) at ./get_df line 21.
Use of uninitialized value in division (/) at ./get_df line 22.
Use of uninitialized value in hash element at ./get_df line 15.
Use of uninitialized value in substitution (s///) at ./get_df line 21.
Use of uninitialized value in division (/) at ./get_df line 22.
Use of uninitialized value in hash element at ./get_df line 15.
Use of uninitialized value in substitution (s///) at ./get_df line 21.
Use of uninitialized value in division (/) at ./get_df line 22.
Use of uninitialized value in hash element at ./get_df line 15.
Use of uninitialized value in substitution (s///) at ./get_df line 21.
Use of uninitialized value in division (/) at ./get_df line 22.
Use of uninitialized value in hash element at ./get_df line 15.
9006792
/production/log is at 70% with 9006792K remaining.
/ is at 37% with 17037532K remaining.
/production is at 11% with 13171728K remaining.
/export/home is at 24% with 11199904K remaining.
/production/archive is at 18% with 8095796K remaining.
/boot is at 28% with 68351K remaining.

更新:我昨晚在家看了CPAN上的DF模块,但我必须获得sysadmin批准才能安装它.在文件系统太长的时候,它被打印到另一行.这搞砸了数据转储器的打印输出 - 一些哈希值被标记为undef.

casper@casperbox]:~/.wjohnson> df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      28313732   9816924  17035356  37% /
/dev/sda1               101086     27516     68351  29% /boot
tmpfs                  2987896         0   2987896   0% /dev/shm
/dev/mapper/VolGroupPROD-ExportHome
                      15481840   3495504  11199904  24% /export/home
/dev/mapper/VolGroupPROD-Production
                      15481840   1523692  13171716  11% /production
/dev/mapper/VolGroupPROD-ProdLog
                      30963708  20410952   8979892  70% /production/log
/dev/mapper/VolGroupPROD-ProdArchive
                      10313016   1693640   8095500  18% /production/archive
[casper@casperbox]:~/.wjohnson>
[casper@casperbox]:~/.wjohnson>
[casper@casperbox]:~/.wjohnson>
[casper@casperbox]:~/.wjohnson>
[casper@casperbox]:~/.wjohnson> df -k | grep -v dev
Filesystem           1K-blocks      Used Available Use% Mounted on
                      28313732   9816924  17035356  37% /
                      15481840   3495504  11199904  24% /export/home
                      15481840   1523692  13171716  11% /production
                      30963708  20410952   8979892  70% /production/log
                      10313016   1693640   8095500  18% /production/archive
[casper@casperbox]:~/.wjohnson>

从Data :: Dumper - 许多哈希值都是未定义的.有没有办法可以预定义哈希的值.我想学会摆脱它们.

$VAR1 = {};
Use of uninitialized value in substitution (s///) at ./get_df.just_capacity line 24.
Use of uninitialized value in division (/) at ./get_df.just_capacity line 25.
Use of uninitialized value in hash element at ./get_df.just_capacity line 17.
$VAR1 = {
          '' => {
                  'free' => undef,
                  'mount' => undef,
                  'used' => undef,
                  'name' => '/dev/mapper/VolGroup00-LogVol00',
                  'capacity' => '0',
                  'size' => undef
            }
        };
$VAR1 = {};
$VAR1 = {
          '' => {
                  'free' => undef,
                  'mount' => undef,
                  'used' => undef,
                  'name' => '/dev/mapper/VolGroup00-LogVol00',
                  'capacity' => '0',
                  'size' => undef
                },

这可以通过使用来解决df -k | grep -v var- 但必须有更好的方法.

Answer 1

perldiag:

使用了未定义的值,就好像它已经定义了一样.它被解释为""或0,但也许这是一个错误.要禁止此警告,请为变量分配定义的值.

为了帮助您找出未定义的内容,perl将尝试告诉您未定义的变量(如果有)的名称.在某些情况下,它无法执行此操作,因此它还会告诉您使用未定义值的操作.但是,请注意,perl会优化您的程序,并且警告中显示的操作可能不一定会出现在您的程序中.例如,"$ foo"通常被优化为"那个".$ foo,警告将引用连接(.)运算符,即使没有.在你的程序中.

简而言之,您使用了一个变量,就好像它包含一个字符串或数字,但它的值undef可能是因为它从未收到过值或者因为它不存在.

也许你使用了错误的变量名.也许您需要提供默认值.原因无数,所以没有单一的解决方案.