Notes: Perl Lab 08

Outline

  1. Join Function
  2. Concatenation
  3. Substrings
  4. length function
  5. Case manipulation

  1. The join function

     The join function joins the elements of a list (array) together as a single string with the individual elements separated by the specified string. While this appears to be simililar to the split function, the first argument cannot be a pattern, it must be a string.

    lab08_0.pl
      
    #!/usr/bin/perl -w 

# Name: Mark Tucker
# Assignment: Lab08 Example 00
# Description: join function examples
#==========================================================================

@greek = qw( alpha beta delta epsilon zeta eta iota gamma theta omega );

# Join array elements together with the * character 
$string_one = join('*', @greek);
print "String 1:\n$string_one\n\n";

# Join array elements together in one continuous string
$string_two = join('', @greek);
print "String 2:\n$string_two\n\n";


# Join array elements together with a variable
$join_str = ':::';
$string_three = join($join_str, $greek[3], $greek[7], $greek[1], $greek[0]);
print "String 3:\n$string_three\n\n";

exit;
# DONE

    When executed, the script above produces the following output:
      
    [mark@iguana perl] ./lab08_0.pl 
String 1:
alpha*beta*delta*epsilon*zeta*eta*iota*gamma*theta*omega

String 2:
alphabetadeltaepsilonzetaetaiotagammathetaomega

String 3:
epsilon:::gamma:::beta:::alpha

[mark@iguana perl]

  2. String Concatenation

     In perl, the concatenation operator is the dot character (.). This can be used to contatenate strings in variable assignment or in other functions such as a print statment.

    lab08_1.pl
      
    #!/usr/bin/perl -w 

# Name: Mark Tucker
# Assignment: Lab08 Example 01
# Description: Concatenation examples
#==========================================================================

@greek = qw( alpha beta delta epsilon zeta eta iota gamma theta omega );

# concatenation during variable assignment
$alphabeta = $greek[0] . $greek[1];
print "Alpha/Beta is $alphabeta\n";

# concatenation in a print statment.
print "This string was written on ".
    "multiple lines but will ".
    "print only one.\n";

exit;
# DONE

    When executed, the script above produces the following output:
      
    [mark@iguana perl] ./lab08_1.pl 
Alpha/Beta is alphabeta
This string was written on multiple lines but will print only one
[mark@iguana perl]

  3. Substrings

     Substrings can be extracted from a string using the substr function. The function uses the following syntax:
    substr($string, $offset, $length)
    In the above statement $string would be the text string from which a substring will be extracted. The $offset and $length define which substring of the original string ($string) will be returned. $offset tells the substr function where to begin the substring. If the substring were to begin with the first character of the string then the value of $offset would be 0. If we wished to start the substring with the third character then the value of $offset$length, defines how long, in characters, the substring will be. $length should be an integer value. Some examples below: lab08_2.pl
      
    #!/usr/bin/perl -w 

# Name: Mark Tucker
# Assignment: Lab08 Example 02
# Description: Substring examples
#==========================================================================

# assign value for a string
$test_string = 'abcdefghijklmnopqrstuvwxyz';

# extract a substring and print to the screen
$newsubstr = substr($test_string, 3, 5);
print "New substring is '$newsubstr'\n";

# extract a substring and print to the screen using variables 
# to define the substring
$strlngth = 7;
$offset = 9;
$second_substr = substr($test_string, $offset, $strlngth);
print "Second substring is '$second_substr'\n";

exit;
# DONE

    When executed, the script above produces the following output:
      
    [mark@iguana perl] ./lab08_2.pl 
New substring is 'defgh'
Second substring is 'jklmnop'
[mark@iguana perl]

  4. The length Function

     The length function simply returns the length of a text string. It is useful when used in conjunction with the substring function. Below is a script with some examples of how to use the length function:

    lab08_3.pl
      
    #!/usr/bin/perl -w 

# Name: Mark Tucker
# Assignment: Lab08 Example 03
# Description: Substring and length()  examples
#==========================================================================

# assign value for a string
$str_one = 'Perl is great!';
$str_two = 'I love Unix!!';
$str_three = 'Computers are evil';

# returning the length and saving in a variable.
$length_two = length($str_two);
print "String two is $length_two characters long.\n";

# Returning the length in a print statement using concatenation
print "String one is " . length($str_one) . " characters long.\n";

# Using the length function inside a substring function
$sl = 4;
$offset = length($str_three) - 4;
$last_four = substr($str_three, $offset, $sl);

#an equivalent statement
$last_four_more = substr($str_three, (length($str_three) -4), 4);

print "The last four characters of '$str_three' are '$last_four' or ".
    "'$last_four_more'.\n";

exit;
# DONE

    When executed, the script above produces the following output:
      
    [mark@iguana perl] ./lab08_3.pl  
String two is 13 characters long.
String one is 14 characters long.
The last four characters of 'Computers are evil' are 'evil' or 'evil'
[mark@iguana perl]

  5. Case Manipulation

     Perl has several functions for altering the case of a string.
    FunctionDescription
    uc($string)Returns the value of $string will all characters converted to upper case
    lc($string)Returns the value of $string with all characters converted to lower case
    ucfirst($string)Returns the value of $string with just the first character converted to uppercase. All other charactes in the string are unchanged.
    lcfirst($string)Returns the value of $string with just the first character converted to lower case. All other characters in the string are unchanged.

    Some examples:

    lab08_4.pl
      
    #!/usr/bin/perl -w 

# Name: Mark Tucker
# Assignment: Lab08 Example 04
# Description: Case manipulation
#==========================================================================

# get the user's name
print "Please enter your name:\n";
chomp($myname = <STDIN>);

# upper case the first character of the string
print "Capitalize: " . ucfirst($myname) . "\n";

# upper case the entire string
print "Upper case: " . uc($myname) . "\n";

# reassing $myname as an upper case string
$myname = uc($myname);

# lower case the first character of the string
print "Lower first: " . lcfirst($myname) . "\n";

# lower case the entire string
print "Lower case: " . lc($myname) . "\n";

exit;
# DONE

    When executed, the script above produces the following output:
      
    [mark@iguana perl] ./lab08_4.pl  
mark tucker
Capitalize: Mark tucker
Upper case: MARK TUCKER
Lower first: mARK TUCKER
Lower case: mark tucker
[mark@iguana perl]

last updated: 18 Mar 2012 13:04