October 30, 2010

Read Binary File in Perl

By Mohammed Abualrob Code Snippets 0 Comments

Problem

Given the path to a directory. Write a Perl script to print the average time to open and read all files in that directory. The files should be read in blocks of 64 KB

Solution

This is straightforward problem but we need to pay attention to the fact that files can grow in size so we should not dump the entire file into memory however we will read the file in chunks. For more details please refer to the code below.

Code

Here is the code in Perl

#!/perl/bin/perl

# Command line argumens
my $Args = "@ARGV";

# Path to the directory containing files
if ($Args =~ /--dir (S+)/)
{
   $dir = $1;
}

# Hardcoded for testing purpose only
$dir = "/perl/test";

# Check tool usage
if (!(defined($dir)))
{
   print "\\n";
   print "Usage: question_one.pl [--dir <dir>]\\n";
   print "\\n";
   exit;
}

print "Please wait...\\n\\n";

# Open directory containing files then read files
opendir(DIR, $dir) || die "can not opendir $dir: $!";
@files = readdir(DIR);
closedir DIR;

# Start time
my $StartTime = time();

# Read files one by one
foreach $file (@files)
{
   # Exclude the following directory entries . and ..
   if ($file !~ m/^.|..$/)
   {
      #Open file in binary mode
      open (F, $dir . "/" . $file) or die "can not open file: $!";
      binmode(F);

      #Read file in 64K blocks
      my ($buf, $data, $n);
      while (($n = read F, $data, 65536) != 0)
      {
         print "Reading $n bytes from file: $file\\n";
         $buf .= $data;
      }
      close(F);
      print "\\n";
   }
}

# End time
my $EndTime = time();

# Elapsed time
my $ElapsedTime = $EndTime - $StartTime;

# Number of files read
my $NumberFiles = $#files - 1;

# Calculate average
if ($NumberFiles > 0 and $ElapsedTime > 0)
{
   my $AverageTime = $ElapsedTime/$NumberFiles;
   print "Number of files read: $NumberFiles\\n";
   print "Average time: $AverageTime\\n";
}
else
{
   print "No files were found or the files are too small\\n";
}

#!/perl/bin/perl

# Command line argumens

my $Args = "@ARGV";

# Path to the directory containing files

if ($Args =~ /--dir (S+)/)

{

$dir = $1;

}

# Hardcoded for testing purpose only

$dir = "/perl/test";

# Check tool usage

if (!(defined($dir)))

{

print "\\n";

print "Usage: question_one.pl [--dir <dir>]\\n";

print "\\n";

exit;

}

print "Please wait...\\n\\n";

# Open directory containing files then read files

opendir(DIR, $dir) || die "can not opendir $dir: $!";

@files = readdir(DIR);

closedir DIR;

# Start time

my $StartTime = time();

# Read files one by one

foreach $file (@files)

{

# Exclude the following directory entries . and ..

if ($file !~ m/^.|..$/)

{

#Open file in binary mode

open (F, $dir . "/" . $file) or die "can not open file: $!";

binmode(F);

#Read file in 64K blocks

my ($buf, $data, $n);

while (($n = read F, $data, 65536) != 0)

{

print "Reading $n bytes from file: $file\\n";

$buf .= $data;

}

close(F);

print "\\n";

}

# End time

my $EndTime = time();

# Elapsed time

my $ElapsedTime = $EndTime - $StartTime;

# Number of files read

my $NumberFiles = $#files - 1;

# Calculate average

if ($NumberFiles > 0 and $ElapsedTime > 0)

{

my $AverageTime = $ElapsedTime/$NumberFiles;

print "Number of files read: $NumberFiles\\n";

print "Average time: $AverageTime\\n";

}

else

{

print "No files were found or the files are too small\\n";

}

8 BIT AVENUE

Read Binary File in Perl

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