perlfaq5.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

.PP
.Vb 2
\&        open my $in,  \*(Aq<\*(Aq,  $file      or die "Can\*(Aqt read old file: $!"
\&        open my $out, \*(Aq>\*(Aq, "$file.new" or die "Can\*(Aqt write new file: $!";
\&
\&        my @lines = do { local $/; <$in> }; # slurp!
\&
\&                # do your magic here
\&
\&        print $out @lines;
.Ve
.PP
Modules such as \f(CW\*(C`File::Slurp\*(C'\fR and \f(CW\*(C`Tie::File\*(C'\fR can help with that
too. If you can, however, avoid reading the entire file at once. Perl
won't give that memory back to the operating system until the process
finishes.
.PP
You can also use Perl one-liners to modify a file in-place. The
following changes all 'Fred' to 'Barney' in \fIinFile.txt\fR, overwriting
the file with the new contents. With the \f(CW\*(C`\-p\*(C'\fR switch, Perl wraps a
\&\f(CW\*(C`while\*(C'\fR loop around the code you specify with \f(CW\*(C`\-e\*(C'\fR, and \f(CW\*(C`\-i\*(C'\fR turns
on in-place editing. The current line is in \f(CW$_\fR. With \f(CW\*(C`\-p\*(C'\fR, Perl
automatically prints the value of \f(CW$_\fR at the end of the loop. See
perlrun for more details.
.PP
.Vb 1
\&        perl \-pi \-e \*(Aqs/Fred/Barney/\*(Aq inFile.txt
.Ve
.PP
To make a backup of \f(CW\*(C`inFile.txt\*(C'\fR, give \f(CW\*(C`\-i\*(C'\fR a file extension to add:
.PP
.Vb 1
\&        perl \-pi.bak \-e \*(Aqs/Fred/Barney/\*(Aq inFile.txt
.Ve
.PP
To change only the fifth line, you can add a test checking \f(CW$.\fR, the
input line number, then only perform the operation when the test
passes:
.PP
.Vb 1
\&        perl \-pi \-e \*(Aqs/Fred/Barney/ if $. == 5\*(Aq inFile.txt
.Ve
.PP
To add lines before a certain line, you can add a line (or lines!)
before Perl prints \f(CW$_\fR:
.PP
.Vb 1
\&        perl \-pi \-e \*(Aqprint "Put before third line\en" if $. == 3\*(Aq inFile.txt
.Ve
.PP
You can even add a line to the beginning of a file, since the current
line prints at the end of the loop:
.PP
.Vb 1
\&        perl \-pi \-e \*(Aqprint "Put before first line\en" if $. == 1\*(Aq inFile.txt
.Ve
.PP
To insert a line after one already in the file, use the \f(CW\*(C`\-n\*(C'\fR switch.
It's just like \f(CW\*(C`\-p\*(C'\fR except that it doesn't print \f(CW$_\fR at the end of
the loop, so you have to do that yourself. In this case, print \f(CW$_\fR
first, then print the line that you want to add.
.PP
.Vb 1
\&        perl \-ni \-e \*(Aqprint; print "Put after fifth line\en" if $. == 5\*(Aq inFile.txt
.Ve
.PP
To delete lines, only print the ones that you want.
.PP
.Vb 1
\&        perl \-ni \-e \*(Aqprint unless /d/\*(Aq inFile.txt
\&
\&                ... or ...
\&
\&        perl \-pi \-e \*(Aqnext unless /d/\*(Aq inFile.txt
.Ve
.Sh "How do I count the number of lines in a file?"
.IX Xref "file, counting lines lines line"
.IX Subsection "How do I count the number of lines in a file?"
One fairly efficient way is to count newlines in the file. The
following program uses a feature of tr///, as documented in perlop.
If your text file doesn't end with a newline, then it's not really a
proper text file, so this may report one fewer line than you expect.
.PP
.Vb 6
\&        $lines = 0;
\&        open(FILE, $filename) or die "Can\*(Aqt open \`$filename\*(Aq: $!";
\&        while (sysread FILE, $buffer, 4096) {
\&                $lines += ($buffer =~ tr/\en//);
\&                }
\&        close FILE;
.Ve
.PP
This assumes no funny games with newline translations.
.ie n .Sh "How can I use Perl's ""\-i"" option from within a program?"
.el .Sh "How can I use Perl's \f(CW\-i\fP option from within a program?"
.IX Xref "-i in-place"
.IX Subsection "How can I use Perl's -i option from within a program?"
\&\f(CW\*(C`\-i\*(C'\fR sets the value of Perl's \f(CW$^I\fR variable, which in turn affects
the behavior of \f(CW\*(C`<>\*(C'\fR; see perlrun for more details.  By
modifying the appropriate variables directly, you can get the same
behavior within a larger program.  For example:
.PP
.Vb 10
\&        # ...
\&        {
\&        local($^I, @ARGV) = (\*(Aq.orig\*(Aq, glob("*.c"));
\&        while (<>) {
\&                if ($. == 1) {
\&                        print "This line should appear at the top of each file\en";
\&                }
\&                s/\eb(p)earl\eb/${1}erl/i;        # Correct typos, preserving case
\&                print;
\&                close ARGV if eof;              # Reset $.
\&                }
\&        }
\&        # $^I and @ARGV return to their old values here
.Ve
.PP
This block modifies all the \f(CW\*(C`.c\*(C'\fR files in the current directory,
leaving a backup of the original data from each file in a new
\&\f(CW\*(C`.c.orig\*(C'\fR file.
.Sh "How can I copy a file?"
.IX Xref "copy file, copy"
.IX Subsection "How can I copy a file?"
(contributed by brian d foy)
.PP
Use the File::Copy module. It comes with Perl and can do a
true copy across file systems, and it does its magic in
a portable fashion.
.PP
.Vb 1
\&        use File::Copy;
\&
\&        copy( $original, $new_copy ) or die "Copy failed: $!";
.Ve
.PP
If you can't use File::Copy, you'll have to do the work yourself:
open the original file, open the destination file, then print
to the destination file as you read the original.
.Sh "How do I make a temporary file name?"
.IX Xref "file, temporary"
.IX Subsection "How do I make a temporary file name?"
If you don't need to know the name of the file, you can use \f(CW\*(C`open()\*(C'\fR
with \f(CW\*(C`undef\*(C'\fR in place of the file name.  The \f(CW\*(C`open()\*(C'\fR function
creates an anonymous temporary file.
.PP
.Vb 1
\&        open my $tmp, \*(Aq+>\*(Aq, undef or die $!;
.Ve
.PP
Otherwise, you can use the File::Temp module.
.PP
.Vb 1
\&        use File::Temp qw/ tempfile tempdir /;
\&
\&        $dir = tempdir( CLEANUP => 1 );
\&        ($fh, $filename) = tempfile( DIR => $dir );
\&
\&        # or if you don\*(Aqt need to know the filename
\&
\&        $fh = tempfile( DIR => $dir );
.Ve
.PP
The File::Temp has been a standard module since Perl 5.6.1.  If you
don't have a modern enough Perl installed, use the \f(CW\*(C`new_tmpfile\*(C'\fR
class method from the IO::File module to get a filehandle opened for
reading and writing.  Use it if you don't need to know the file's name:
.PP
.Vb 3
\&        use IO::File;
\&        $fh = IO::File\->new_tmpfile()
\&        or die "Unable to make new temporary file: $!";
.Ve
.PP
If you're committed to creating a temporary file by hand, use the
process \s-1ID\s0 and/or the current time-value.  If you need to have many
temporary files in one process, use a counter:
.PP
.Vb 4
\&        BEGIN {
\&        use Fcntl;
\&        my $temp_dir = \-d \*(Aq/tmp\*(Aq ? \*(Aq/tmp\*(Aq : $ENV{TMPDIR} || $ENV{TEMP};
\&        my $base_name = sprintf "%s/%d\-%d\-0000", $temp_dir, $$, time;
\&
\&        sub temp_file {
\&                local *FH;
\&                my $count = 0;
\&                until( defined(fileno(FH)) || $count++ > 100 ) {
\&                        $base_name =~ s/\-(\ed+)$/"\-" . (1 + $1)/e;
\&                        # O_EXCL is required for security reasons.
\&                        sysopen FH, $base_name, O_WRONLY|O_EXCL|O_CREAT;
\&                        }
\&
\&                if( defined fileno(FH) ) {
\&                        return (*FH, $base_name);
\&                        }
\&                else {
\&                        return ();
\&                        }
\&                }
\&                
\&        }
.Ve
.Sh "How can I manipulate fixed-record-length files?"
.IX Xref "fixed-length file, fixed-length records"
.IX Subsection "How can I manipulate fixed-record-length files?"
The most efficient way is using \fIpack()\fR and
\&\fIunpack()\fR.  This is faster than using
\&\fIsubstr()\fR when taking many, many strings.  It is
slower for just a few.
.PP
Here is a sample chunk of code to break up and put back together again
some fixed-format input lines, in this case from the output of a normal,
Berkeley-style ps:
.PP
.Vb 10
\&        # sample input line:
\&        #   15158 p5  T      0:00 perl /home/tchrist/scripts/now\-what
\&        my $PS_T = \*(AqA6 A4 A7 A5 A*\*(Aq;
\&        open my $ps, \*(Aq\-|\*(Aq, \*(Aqps\*(Aq;
\&        print scalar <$ps>;
\&        my @fields = qw( pid tt stat time command );
\&        while (<$ps>) {
\&                my %process;
\&                @process{@fields} = unpack($PS_T, $_);
\&        for my $field ( @fields ) {
\&                print "$field: <$process{$field}>\en";
\&        }
\&        print \*(Aqline=\*(Aq, pack($PS_T, @process{@fields} ), "\en";
\&        }
.Ve
.PP
We've used a hash slice in order to easily handle the fields of each row.
Storing the keys in an array means it's easy to operate on them as a
group or loop over them with for. It also avoids polluting the program
with global variables and using symbolic references.
.Sh "How can I make a filehandle local to a subroutine?  How do I pass filehandles between subroutines?  How do I make an array of filehandles?"
.IX Xref "filehandle, local filehandle, passing filehandle, reference"
.IX Subsection "How can I make a filehandle local to a subroutine?  How do I pass filehandles between subroutines?  How do I make an array of filehandles?"
As of perl5.6, \fIopen()\fR autovivifies file and directory handles
as references if you pass it an uninitialized scalar variable.
You can then pass these references just like any other scalar,
and use them in the place of named handles.
.PP
.Vb 1
\&        open my    $fh, $file_name;
\&
\&        open local $fh, $file_name;
\&
\&        print $fh "Hello World!\en";
\&
\&        process_file( $fh );
.Ve
.PP
If you like, you can store these filehandles in an array or a hash.
If you access them directly, they aren't simple scalars and you
need to give \f(CW\*(C`print\*(C'\fR a little help by placing the filehandle
reference in braces. Perl can only figure it out on its own when
the filehandle reference is a simple scalar.
.PP
.Vb 1
\&        my @fhs = ( $fh1, $fh2, $fh3 );
\&
\&        for( $i = 0; $i <= $#fhs; $i++ ) {
\&                print {$fhs[$i]} "just another Perl answer, \en";
\&                }
.Ve
.PP
Before perl5.6, you had to deal with various typeglob idioms
which you may see in older code.
.PP
.Vb 3
\&        open FILE, "> $filename";
\&        process_typeglob(   *FILE );
\&        process_reference( \e*FILE );
\&
\&        sub process_typeglob  { local *FH = shift; print FH  "Typeglob!" }
\&        sub process_reference { local $fh = shift; print $fh "Reference!" }
.Ve
.PP
If you want to create many anonymous handles, you should
check out the Symbol or IO::Handle modules.
.Sh "How can I use a filehandle indirectly?"
.IX Xref "filehandle, indirect"
.IX Subsection "How can I use a filehandle indirectly?"
An indirect filehandle is using something other than a symbol
in a place that a filehandle is expected.  Here are ways
to get indirect filehandles:
.PP
.Vb 5
\&        $fh =   SOME_FH;       # bareword is strict\-subs hostile
\&        $fh =  "SOME_FH";      # strict\-refs hostile; same package only
\&        $fh =  *SOME_FH;       # typeglob
\&        $fh = \e*SOME_FH;       # ref to typeglob (bless\-able)
\&        $fh =  *SOME_FH{IO};   # blessed IO::Handle from *SOME_FH typeglob
.Ve
.PP
Or, you can use the \f(CW\*(C`new\*(C'\fR method from one of the IO::* modules to
create an anonymous filehandle, store that in a scalar variable,
and use it as though it were a normal filehandle.
.PP
.Vb 2
\&        use IO::Handle;                     # 5.004 or higher
\&        $fh = IO::Handle\->new();
.Ve
.PP
Then use any of those as you would a normal filehandle.  Anywhere that
Perl is expecting a filehandle, an indirect filehandle may be used
instead. An indirect filehandle is just a scalar variable that contains
a filehandle.  Functions like \f(CW\*(C`print\*(C'\fR, \f(CW\*(C`open\*(C'\fR, \f(CW\*(C`seek\*(C'\fR, or
the \f(CW\*(C`<FH>\*(C'\fR diamond operator will accept either a named filehandle
or a scalar variable containing one:
.PP
.Vb 4
\&        ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR);
\&        print $ofh "Type it: ";
\&        $got = <$ifh>
\&        print $efh "What was that: $got";
.Ve
.PP
If you're passing a filehandle to a function, you can write
the function in two ways: