Lists, Arrays, and Hashes

List Assignment

List assignment copies several values into several scalar variables in order.

list assignment List assignment places each value from the right side into the matching variable on the left side.

List Assignment

middle
list_assignment.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

my $middle = "green";
my ($first, $second, $third) = ("red", $middle, "blue");
my $summary = "$first,$second,$third";

print "first=$first\n";
print "second=$second\n";
print "summary=$summary\n";

use strict;
use warnings;

my $middle = "yellow";
my ($first, $second, $third) = ("red", $middle, "blue");
my $summary = "$first,$second,$third";

print "first=$first\n";
print "second=$second\n";
print "summary=$summary\n";

use strict;
use warnings;

my $middle = "purple";
my ($first, $second, $third) = ("red", $middle, "blue");
my $summary = "$first,$second,$third";

print "first=$first\n";
print "second=$second\n";
print "summary=$summary\n";

  1. $middle ← green, $first ← red, $second ← green, $third ← blue

    4my $middle→ green = "green"; #@middle="yellow", "purple"5my ($first→ red, $second→ green, $third→ blue) = ("red", $middlegreen, "blue");6my $summary→ red,green,blue = "$firstred,$secondgreen,$thirdblue";78print "first=$firstred\n";9print "second=$secondgreen\n";10print "summary=$summaryred,green,blue\n";
    outputfirst=red
second=green
summary=red,green,blue

  1. $middle ← yellow, $first ← red, $second ← yellow, $third ← blue

    4my $middle→ yellow = "yellow";5my ($first→ red, $second→ yellow, $third→ blue) = ("red", $middleyellow, "blue");6my $summary→ red,yellow,blue = "$firstred,$secondyellow,$thirdblue";78print "first=$firstred\n";9print "second=$secondyellow\n";10print "summary=$summaryred,yellow,blue\n";
    outputfirst=red
second=yellow
summary=red,yellow,blue

  1. $middle ← purple, $first ← red, $second ← purple, $third ← blue

    4my $middle→ purple = "purple";5my ($first→ red, $second→ purple, $third→ blue) = ("red", $middlepurple, "blue");6my $summary→ red,purple,blue = "$firstred,$secondpurple,$thirdblue";78print "first=$firstred\n";9print "second=$secondpurple\n";10print "summary=$summaryred,purple,blue\n";
    outputfirst=red
second=purple
summary=red,purple,blue

Assign in Order

  1. $middle starts as green.
  2. The right-side list is red, green, blue.
  3. Perl assigns each value to the matching variable on the left.
  4. The summary joins the three scalar values with commas. | Position | Variable | Value | | --- | --- | --- | | 1 | $first | red | | 2 | $second | green | | 3 | $third | blue |

Exercise: list_assignment.pl

Assign three list values into scalar variables and print a comma-separated summary