熟悉perl 朋友帮忙指点一下这个脚本？

xqf

刚学习perl

这个代码：        printf "#d dd of=\$origin seek=%.0f if=\$cow iflag=direct skip=%.0f count=%u bs=%ub\n",
                $old, $new, $merge_count, $header->{chunk_size};
       
为什么只能运行打印出来，不执行运行呢
./dm /dev/sdb

\$origin  \$cow 不赋予变量真实的值

谢谢


完整代码如下：

1. #!/usr/bin/perl
   
2. use Fcntl qw(:DEFAULT O_DIRECT);
   
3. 
   
4. use strict;
   
5. use warnings;
   
6. 
   
7. my $file = $ARGV[0] or die "usage: $0 <input device or file>\n";
   
8. 
   
9. # max exception chunk size apears to be 512k
   
10. # we need an aligned buffer for O_DIRECT.
    
11. # dirty trick to get a PAGE_ALIGNed buffer in perl
    
12. # be _very_ careful with $buf, do not touch it,
    
13. # and do not assign to it, not even implicitly!
    
14. my $bufsize = 512*1024;
    
15. my $align = 4096;
    
16. my $buf = "x" x ($bufsize + $align);
    
17. my $offset = $align - (unpack "l", pack "p", $buf) % $align;
    
18. 
    
19. my $header = { magic => 0, valid => 0, version => 0, chunk_size => 0, };
    
20. 
    
21. sysopen(IN, $file, O_RDONLY | O_DIRECT) or die "sysopen($file, O_DIRECT): $!\n";
    
22. 
    
23. sub read_header()
    
24. {
    
25.         my $c = sysread(IN, $buf, 512, $offset);
    
26.         die "problem reading header, \$c: $c, \$!: $!"
    
27.                  if ($c != 512);
    
28.          <at> {$header}{qw(magic valid version chunk_size)} =
    
29.                 unpack "A4VVV", substr($buf, $offset, 512);
    
30. 
    
31.         die "does not appear to be a lvm-snapshot-cow device"
    
32.                 if $header->{magic} ne 'SnAp';
    
33.         die "cannot deal with this snapshot version"
    
34.                 if $header->{version} != 1;
    
35.         die "snapshot is invalid, refusing to operate on it"
    
36.                 unless $header->{valid};
    
37.         die "unexpected chunk size"
    
38.                 if ($header->{chunk_size} & ($header->{chunk_size}-1)) != 0;
    
39.         printf "# found snapshot header for chunk_size=%u sectors\n", $header->{chunk_size};
    
40. }
    
41. 
    
42. sub seek_to_exception_table($)
    
43. {
    
44.         my $n = $_[0];
    
45.         my $cs = $header->{chunk_size} * 512;
    
46.         my $epc = $cs / 16;
    
47.         my $pos = ($n*($epc+1)+1)*$cs;
    
48.         sysseek(IN, $pos, 0) == $pos
    
49.                 or die "sysseek(,$pos,): $!";
    
50. }
    
51. 
    
52. sub process_one_exception
    
53. {
    
54.         my ($old,$new,$merge_count) =  <at> _;
    
55.         # chunk numbers!
    
56.         # old: logical chunk number
    
57.         # new: chunk number in exception store
    
58.         # merge count: how many chunks could be merged
    
59.         # with these start sectors
    
60. 
    
61.         # chunk number mapping
    
62.         # printf "#c %20.0f\t%20.0f\t%u\n", $old, $new, $merge_count;
    
63. 
    
64.         # for sectors you'd have to multiply with $header->{chunk_size};
    
65. 
    
66.         # dd command line
    
67.         # if you dare,
    
68.         # you can do it in perl directly!
    
69.         # or implement it in C using pread/pwrite.
    
70.         printf "#d dd of=\$origin seek=%.0f if=\$cow iflag=direct skip=%.0f count=%u bs=%ub\n",
    
71.                 $old, $new, $merge_count, $header->{chunk_size};
    
72.        
    
73. }
    
74. 
    
75. sub list_exceptions()
    
76. {
    
77.         my $cs = 512*$header->{chunk_size};
    
78.         my $enr = 0;
    
79.         my $ecount = 0;
    
80.         my $e;
    
81.         my  <at> t;
    
82. EXCEPTION_CHUNK:
    
83.         for ($enr = 0; seek_to_exception_table($enr); $enr++) {
    
84.                 my $c = sysread(IN, $buf, $cs, $offset);
    
85.                 die "problem reading exception table, \$c: $c, \$!: $!"
    
86.                          if ($c != $cs);
    
87.                  <at> t = unpack "V*", substr($buf, $offset, $cs);
    
88.                 for (my $i = 0; $i <  <at> t; $i += 4) {
    
89.                         # if the "new" location is equal to zero,
    
90.                         # that was the END marker.
    
91.                         last EXCEPTION_CHUNK unless $t[$i+2] || $t[$i+3];
    
92.                         $ecount++;
    
93. 
    
94.                         # unfortunately 64bit integer is not available
    
95.                         # in many perl. we compensate:
    
96.                         my ($old,$new) = (
    
97.                                 $t[$i+1] * 4294967296.0 + $t[$i],
    
98.                                 $t[$i+3] * 4294967296.0 + $t[$i+2]);
    
99. 
    
100.                         # maybe we can merge?
     
101.                         if ($e and
     
102.                                 $old == $e->[0] + $e->[2] and
     
103.                                 $new == $e->[1] + $e->[2])
     
104.                         {
     
105.                                 $e->[2]++;
     
106.                                 next;
     
107.                         }
     
108.                         process_one_exception( <at> $e) if $e;
     
109.                         $e = [ $old, $new, 1]
     
110.                 }
     
111.                 process_one_exception( <at> $e);
     
112.                 # would not work anyways, $new mapping jumps, but lets
     
113.                 # _explicitly_ only merge within one exception table chunk
     
114.                 undef $e;
     
115.         }
     
116.         # don't forget to report the last mapping
     
117.         process_one_exception( <at> $e) if $e;
     
118.         printf "# found %.0f exceptions (%.0f kB)\n",
     
119.                 $ecount, $ecount*$header->{chunk_size}/2;
     
120.         print "## use these dd commands AT YOUR OWN RISK\n" if $ecount;
     
121. }
     
122. 
     
123. read_header;
     
124. list_exceptions;

复制代码

xqf

perl ？？？？难道真没有人知道吗

yybmsrs

注释说的很清楚了

yybmsrs

        # dd command line
        # if you dare,
        # you can do it in perl directly!
        # or implement it in C using pread/pwrite.

xqf

但是只是格左化打印出来没有执行真实的打操作： ./dm.sh /dev/loop0 /dev/loop1 是这样的吗