If and Switch Statements¶

Control flow determines which code runs based on conditions. PowerShell provides two primary branching constructs: if and switch. Both evaluate expressions and execute different blocks of code depending on the result.

1. if¶

The if statement runs a block of code only when a condition is true.

The basic syntax is:

if (<condition>) {
    <code>
}

A condition is any expression that returns $true or $false.

1.1 Basic example¶

$age = 20

if ($age -ge 18) {
    "You are an adult."
}

Explanation:

• $age -ge 18 evaluates to $true.
• The code inside the braces runs.
• The output is "You are an adult.".

1.2 if / else¶

$number = 5

if ($number -gt 10) {
    "Greater than 10"
} else {
    "10 or less"
}

Explanation:

• $number -gt 10 is $false.
• The else block runs.

1.3 if / elseif / else¶

$score = 75

if ($score -ge 90) {
    "Grade: A"
} elseif ($score -ge 80) {
    "Grade: B"
} elseif ($score -ge 70) {
    "Grade: C"
} else {
    "Grade: D"
}

Explanation:

• PowerShell evaluates each condition in order.
• $score -ge 70 is the first true condition.
• "Grade: C" is printed.

1.4 Using if with strings¶

$name = "Alice"

if ($name -eq "Alice") {
    "Welcome, Alice."
}

String comparisons are case‑insensitive by default.

1.5 Using if with logical operators¶

$age = 30
$member = $true

if ($age -ge 18 -and $member) {
    "Access granted."
}

Explanation:

• Both conditions must be true for the block to run.

2. switch¶

switch evaluates a value against multiple possible matches.

It is cleaner than writing many elseif statements.

Basic syntax:

switch (<value>) {
    <match1> { <code> }
    <match2> { <code> }
    default  { <code> }
}

PowerShell compares the value to each match and runs the corresponding block.

2.1 Basic example¶

$color = "green"

switch ($color) {
    "red"   { "Stop" }
    "yellow"{ "Caution" }
    "green" { "Go" }
}

Explanation:

• $color is "green".
• PowerShell finds the matching label "green".
• It runs the "Go" block.

2.2 Using default¶

$day = "Monday"

switch ($day) {
    "Saturday" { "Weekend" }
    "Sunday"   { "Weekend" }
    default    { "Weekday" }
}

Explanation:

• "Monday" does not match "Saturday" or "Sunday".
• The default block runs.

2.3 Multiple matches¶

A single block can match multiple values:

$input = "y"

switch ($input) {
    "y" { "Yes" }
    "Y" { "Yes" }
    "n" { "No" }
    "N" { "No" }
}

This can be simplified:

switch ($input) {
    "y" { "Yes" }
    "n" { "No" }
    default { "Invalid input" }
}

Because comparisons are case‑insensitive by default.

2.4 Pattern matching with switch¶

switch supports wildcards when you specify the -Wildcard flag:

$filename = "report_2024.txt"

switch -Wildcard ($filename) {
    "report_*" { "This is a report file." }
    "*.txt"    { "This is a text file." }
}

Explanation:

• "report_*" matches first, so that block runs.

2.5 Using switch with script blocks¶

You can use conditions inside each case:

$number = 15

switch ($number) {
    { $_ -lt 10 } { "Less than 10" }
    { $_ -lt 20 } { "Between 10 and 19" }
    default       { "20 or more" }
}

Explanation:

• $_ represents the current value (15).
• The first condition is false.
• The second condition is true.
• "Between 10 and 19" is printed.