Text Processing

Tom Kelliher, CS29

Mar. 4, 1997

1. Reading?

2. Return quizzes.

3. Analyze two problems:
   1. Write a ``tee'' program that sends keyboard input to several output locations, translating all lowercase characters to uppercase (i.e., yelling). The program should terminate when EOF is received.

   2. Write a simple database query program. The database file consists of records with two fields:
      • Name.

      • Phone number.

      The field terminator is a : .

      The program should read the file into a list and then accept queries (name), printing the corresponding phone number or an error message. The program should terminate when EOF is received.

Tee

Keys:

1. The general method of opening files for reading, writing.

2. EOF and indicating it from the keyboard.

3. The character translation operator.

Design of pseudo-code.

A working program:

#!/usr/contrib/bin/perl -w

# upcase.pl

if (!open(FILE1, ">file1"))
{
    die "Couldn't open file1";
}

if (!open(FILE2, ">file2"))
{
    die "Couldn't open file2";
}

$line = <STDIN>;

while ($line)
{
    $line =~ tr/a-z/A-Z/;
    print $line;
    print FILE1 $line;
    print FILE2 $line;

    $line = <STDIN>;
}

close(FILE1);
close(FILE2);

exit 0;

Database Query

Keys:

1. Elegance vs. getting the job done.

2. Lists in perl.

3. Format of the database file:

   Tom:946-3544:
   Mary:946-1234:
   Joe:946-5678:
   

4. The && (logical and) operator and compound conditions.

5. String matching.

6. The split function.

7. Nested loops.

Design of Pseudo-code.

A working program:

#!/usr/contrib/bin/perl -w

# database.pl

print "Enter file name: ";
$file = <STDIN>;
chop($file);

if (!open(FILE, "<$file"))
{
    die "Couldn't open $file";
}

$line = <FILE>;
$last = 0;

while ($line)
{
    $lines[$last] = $line;
    $last = $last + 1;

    $line = <FILE>;
}

close(FILE);

print "Enter a name: ";
$name = <STDIN>;

while ($name)
{
    chop($name);

    $i = 0;
    $found = 0;

    while (!$found && $i < $last)
    {

        if ($lines[$i] =~ /$name/)
        {
            $found = 1;
            @fields = split(/:/, $lines[$i]);
            print "Phone number: $fields[1]\n\n";
        }
        else
        {
            $i = $i + 1;
        }
    }

    if (!$found)
    {
        print "Couldn't find $name.\n\n";
    }

    print "Enter a name: ";
    $name = <STDIN>;
}

exit 0;