?? ch9.htm
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This program displays:<BR>
<BLOCKQUOTE>
<PRE>
30 31 0d 0a
30 32 0d 0a
30 33 0d 0a
</PRE>
</BLOCKQUOTE>
<P>
When the file is read in binary mode, you can see that there are
really two characters at the end of every line-the linefeed and
newline characters.
<P>
Our next example will look at the end-of-file character in both
text and binary modes. We'll use a data file called <TT>EOF.DAT</TT>
with the following contents:
<BLOCKQUOTE>
<PRE>
01
02
<end of file character>03
</PRE>
</BLOCKQUOTE>
<P>
SiNCe the end-of-file character is a non-printing character, it
can't be shown directly. In the spot <TT><end
of file character></TT> above is really the value 26.
<P>
Here is the program that you saw previously read the BINARY.DAT
file, only this time, it will read EOF.DAT.
<P>
<IMG SRC="pseudo.gif" tppabs="http://cheminf.nankai.edu.cn/~eb~/Perl%205%20By%20Example/pseudo.gif" BORDER=1 ALIGN=RIGHT><p>
<BLOCKQUOTE>
<I>Initialize a buffer variable.<BR>
Open the </I><TT><I>BINARY.DAT</I></TT><I>
file for reading.<BR>
Read the first 20 characters of the file using the </I><TT><I>read()</I></TT><I>
fuNCtion.<BR>
Close the file.<BR>
Create an array of out of the characters in the </I><TT><I>$buffer</I></TT><I>
variable and iterate over that array using a </I><TT><I>foreach</I></TT><I>
loop.<BR>
Print the value of the current array element in hexadecimal format.
<BR>
Print a newline character. The current array element is a newline
character.</I>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<B>Listing 9.10 09LST10.PL-Reading a File to Show the
Text Mode End-of-File Character<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
$buffer = "";
open(FILE, "<eof.dat");
read(FILE, $buffer, 20, 0);
close(FILE);
foreach (split(//, $buffer)) {
printf("%02x ", ord($_));
print "\n" if $_ eq "\n";
}
</PRE>
</BLOCKQUOTE>
<HR>
<P>
This program displays:
<BLOCKQUOTE>
<PRE>
30 31 0d 0a
30 32 0d 0a
</PRE>
</BLOCKQUOTE>
<P>
The end-of-file character prevents the read() fuNCtion from reading
the third line. If the file is placed into binary mode, the whole
file can be read.
<P>
<IMG SRC="pseudo.gif" tppabs="http://cheminf.nankai.edu.cn/~eb~/Perl%205%20By%20Example/pseudo.gif" BORDER=1 ALIGN=RIGHT><p>
<BLOCKQUOTE>
<I>Initialize a buffer variable.<BR>
Open the </I><TT><I>BINARY.DAT</I></TT><I>
file for reading.<BR>
Change the mode to binary.<BR>
Read the first 20 characters of the file using the </I><TT><I>read()</I></TT><I>
fuNCtion.<BR>
Close the file.<BR>
Create an array of out of the characters in the </I><TT><I>$buffer</I></TT><I>
variable and iterate over that array using a </I><TT><I>foreach</I></TT><I>
loop.<BR>
Print the value of the current array element in hexadecimal format.
<BR>
Print a newline character. The current array element is a newline
character.</I>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<B>Listing 9.11 09LST11.PL-Reading a File to Show that
Binary Mode Does Not Recognize the End-of-File Character<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
$buffer = "";
open(FILE, "<eof.dat");
binmode(FILE);
read(FILE, $buffer, 20, 0);
close(FILE);
foreach (split(//, $buffer)) {
printf("%02x ", ord($_));
print "\n" if $_ eq "\n";
}
</PRE>
</BLOCKQUOTE>
<HR>
<P>
This program displays:
<BLOCKQUOTE>
<PRE>
30 31 0d 0a
30 32 0d 0a
1a 30 33 0d 0a
</PRE>
</BLOCKQUOTE>
<P>
With binary mode on, bytes with a value of 26 have no special
meaning and the third line can be read. You see that the value
26-33 in hexadecimal-was printed along with the rest of the characters.
<P>
<TT>Example: Reading into a Hash</TT>
<P>
You've already seen that you can read a file directly into a regular
array using this syntax:
<BLOCKQUOTE>
<PRE>
@array = <FILE_HANDLE>;
</PRE>
</BLOCKQUOTE>
<P>
Unfortunately, there is no similar way to read an entire file
into a hash. But, it's still pretty easy to do. The following
example will use the line number as the hash key for each line
of a file.
<P>
<IMG SRC="pseudo.gif" tppabs="http://cheminf.nankai.edu.cn/~eb~/Perl%205%20By%20Example/pseudo.gif" BORDER=1 ALIGN=RIGHT><p>
<BLOCKQUOTE>
<I>Open the </I><TT><I>FIXED.DAT</I></TT><I>
file for reading.<BR>
For each line of </I><TT><I>FIXED.DAT </I></TT><I>create
a hash element using the record number special variable (</I><TT><I>$.</I></TT><I>)
as the key and the line of input (</I><TT><I>$_</I></TT><I>)
as the value.<BR>
Close the file.<BR>
Iterate over the keys of the hash.<BR>
Print each key, value pair.</I>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<B>Listing 9.12 09LST12.PL-Reading a Fixed Length Record
with Fixed Length Fields into a Hash<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
open(FILE, "<fixed.dat");
while (<FILE>) {
$hash{$.} = $_;
}
close(FILE);
foreach (keys %hash) {
print("$_: $hash{$_}");
}
</PRE>
</BLOCKQUOTE>
<HR>
<P>
This program displays:<BR>
<BLOCKQUOTE>
<PRE>
1: 1212Jan Jaspree Painter
2: 3453Kelly Horton Jockey
</PRE>
</BLOCKQUOTE>
<H3><A NAME="ExampleGettingFileStatistics">
Example: Getting File Statistics</A></H3>
<P>
The file test operators can tell you a lot about a file, but sometimes
you need more. In those cases, you use the <TT>stat()</TT>
or <TT>lstat()</TT> fuNCtion. The
<TT>stat()</TT> returns file information
in a 13-element array. You can pass either a file handle or a
file name as the parameter. If the file can't be found or another
error occurs, the null list is returned. Listing 9.13 shows how
to use the <TT>stat()</TT> fuNCtion
to find out information about the <TT>EOF.DAT</TT>
file used earlier in the chapter.
<P>
<IMG SRC="pseudo.gif" tppabs="http://cheminf.nankai.edu.cn/~eb~/Perl%205%20By%20Example/pseudo.gif" BORDER=1 ALIGN=RIGHT><p>
<BLOCKQUOTE>
<I>Assign the return list from the </I><TT><I>stat()</I></TT><I>
fuNCtion to 13 scalar variables.<BR>
Print the scalar values.</I>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<B>Listing 9.13 09LST13.PL-Using the </B><TT><I><B><FONT FACE="Courier">stat()</FONT></B></I></TT><B>
FuNCtion<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<PRE>
($dev, $ino, $mode, $nlink, $uid, $gid, $rdev, $size,
$atime, $mtime, $ctime, $blksize, $blocks) = stat("eof.dat");
print("dev = $dev\n");
print("ino = $ino\n");
print("mode = $mode\n");
print("nlink = $nlink\n");
print("uid = $uid\n");
print("gid = $gid\n");
print("rdev = $rdev\n");
print("size = $size\n");
print("atime = $atime\n");
print("mtime = $mtime\n");
print("ctime = $ctime\n");
print("blksize = $blksize\n");
print("blocks = $blocks\n");
</PRE>
</BLOCKQUOTE>
<HR>
<P>
In the DOS environment, this program displays:
<BLOCKQUOTE>
<PRE>
dev = 2
ino = 0
mode = 33206
nlink = 1
uid = 0
gid = 0
rdev = 2
size = 13
atime = 833137200
mtime = 833195316
ctime = 833194411
blksize =
blocks =
</PRE>
</BLOCKQUOTE>
<P>
Some of this information is specific to the UNIX environment and
is beyond the scope of this book. For more information on this
topic, see Que's 1994 edition of <I>Using Unix</I>. One interesting
piece of information is the <TT>$mtime</TT>
value-the date and time of the last modification made to the file.
You can interpret this value by using the following line of code:
<BLOCKQUOTE>
<PRE>
($sec, $min, $hr, $day, $month, $year, $day_Of_Week,
$julianDate, $dst) = localtime($mtime);
</PRE>
</BLOCKQUOTE>
<P>
If you are only interested in the modification date, you can use
the array slice notation to just grab that value from the 13-element
array returned by <TT>stat()</TT>.
For example:
<BLOCKQUOTE>
<PRE>
$mtime = (stat("eof.dat"))[9];
</PRE>
</BLOCKQUOTE>
<P>
Notice that the <TT>stat()</TT> fuNCtion
is surrounded by parentheses so that the return value is evaluated
in an array context. Then the tenth element is assigned to <TT>$mtime</TT>.
You can use this technique whenever a fuNCtion returns a list.
<H3><A NAME="ExampleUsingtheDirectoryFuNCtions">
Example: Using the Directory FuNCtions</A></H3>
<P>
Perl has several fuNCtions that let you work with directories.
You can make a directory with the <TT>mkdir()</TT>
fuNCtion. You can delete a directory with the <TT>rmdir()</TT>
fuNCtion. Switching from the current directory to another is done
using the <TT>chdir()</TT> fuNCtion.
<P>
Finding out which files are in a directory is done with the <TT>opendir()</TT>,
<TT>readdir()</TT>, and <TT>closedir()</TT>
fuNCtions. The next example will show you how to create a list
of all Perl programs in the current directory-well, at least those
files that end with the pl extension.
<P>
<IMG SRC="pseudo.gif" tppabs="http://cheminf.nankai.edu.cn/~eb~/Perl%205%20By%20Example/pseudo.gif" BORDER=1 ALIGN=RIGHT><p>
<BLOCKQUOTE>
<I>Open the current directory using </I><TT><I>DIR</I></TT><I>
as the directory handle.<BR>
Read a list of file names using the </I><TT><I>readdir()</I></TT><I>
fuNCtion; extract only those that end in </I><TT><I>pl</I></TT><I>;
and the sorted list. The sorted list is assigned to the </I><TT><I>@files</I></TT><I>
array variable.<BR>
Close the directory.<BR>
Print the file names from the </I><TT><I>@files</I></TT><I>
array unless the file is a directory.</I>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<B>Listing 9.14 09LST14.PL-Print All Files in the Current
Directory Whose Name Ends in PL<BR>
</B>
</BLOCKQUOTE>
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