会python真的可以为所欲为0(回)
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这里还有人吗1(回)
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每天面对着电脑屏幕，敲打键盘。我所面对的并不只是代码，而是一种生活方式。0(回)
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839天前
鸽子
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843天前#----------------------------- |
# looking for line number $DESIRED_LINE_NUMBER |
$. = 0; |
do { $LINE = <HANDLE> } until $. == $DESIRED_LINE_NUMBER || eof; |
#----------------------------- |
@lines = <HANDLE>; |
$LINE = $lines[$DESIRED_LINE_NUMBER]; |
#----------------------------- |
# usage: build_index(*DATA_HANDLE, *INDEX_HANDLE) |
sub build_index { |
my $data_file = shift; |
my $index_file = shift; |
my $offset = 0; |
while (<$data_file>) { |
print $index_file pack("N", $offset); |
$offset = tell($data_file); |
} |
} |
# usage: line_with_index(*DATA_HANDLE, *INDEX_HANDLE, $LINE_NUMBER) |
# returns line or undef if LINE_NUMBER was out of range |
sub line_with_index { |
my $data_file = shift; |
my $index_file = shift; |
my $line_number = shift; |
my $size; # size of an index entry |
my $i_offset; # offset into the index of the entry |
my $entry; # index entry |
my $d_offset; # offset into the data file |
$size = length(pack("N", 0)); |
$i_offset = $size * ($line_number-1); |
seek($index_file, $i_offset, 0) or return; |
read($index_file, $entry, $size); |
$d_offset = unpack("N", $entry); |
seek($data_file, $d_offset, 0); |
return scalar(<$data_file>); |
} |
# usage: |
open(FILE, "< $file") or die "Can't open $file for reading: $!\n"; |
open(INDEX, "+>$file.idx") |
or die "Can't open $file.idx for read/write: $!\n"; |
build_index(*FILE, *INDEX); |
$line = line_with_index(*FILE, *INDEX, $seeking); |
#----------------------------- |
use DB_File; |
use Fcntl; |
$tie = tie(@lines, $FILE, "DB_File", O_RDWR, 0666, $DB_RECNO) or die |
"Cannot open file $FILE: $!\n"; |
# extract it |
$line = $lines[$sought - 1]; |
#----------------------------- |
# download the following standalone program |
#!/usr/bin/perl -w |
# print_line-v1 - linear style |
@ARGV == 2 or die "usage: print_line FILENAME LINE_NUMBER\n"; |
($filename, $line_number) = @ARGV; |
open(INFILE, "< $filename") or die "Can't open $filename for reading: $!\n"; |
while (<INFILE>) { |
$line = $_; |
last if $. == $line_number; |
} |
if ($. != $line_number) { |
die "Didn't find line $line_number in $filename\n"; |
} |
print; |
#----------------------------- |
# download the following standalone program |
#!/usr/bin/perl -w |
# print_line-v2 - index style |
# build_index and line_with_index from above |
@ARGV == 2 or |
die "usage: print_line FILENAME LINE_NUMBER"; |
($filename, $line_number) = @ARGV; |
open(ORIG, "< $filename") |
or die "Can't open $filename for reading: $!"; |
# open the index and build it if necessary |
# there's a race condition here: two copies of this |
# program can notice there's no index for the file and |
# try to build one. This would be easily solved with |
# locking |
$indexname = "$filename.index"; |
sysopen(IDX, $indexname, O_CREAT|O_RDWR) |
or die "Can't open $indexname for read/write: $!"; |
build_index(*ORIG, *IDX) if -z $indexname; # XXX: race unless lock |
$line = line_with_index(*ORIG, *IDX, $line_number); |
die "Didn't find line $line_number in $filename" unless defined $line; |
print $line; |
#----------------------------- |
# download the following standalone program |
#!/usr/bin/perl -w |
# print_line-v3 - DB_File style |
use DB_File; |
use Fcntl; |
@ARGV == 2 or |
die "usage: print_line FILENAME LINE_NUMBER\n"; |
($filename, $line_number) = @ARGV; |
$tie = tie(@lines, "DB_File", $filename, O_RDWR, 0666, $DB_RECNO) |
or die "Cannot open file $filename: $!\n"; |
unless ($line_number < $tie->length) { |
die "Didn't find line $line_number in $filename\n" |
} |
print $lines[$line_number-1]; # easy, eh? |
#----------------------------- |
