[Unix] C Shell (csh) else: Conditional execution in scripts

Overview

The else command in C Shell (csh) is used as part of conditional statements to execute a block of code when the preceding if condition evaluates to false. It allows for more complex decision-making in scripts by providing an alternative path of execution.

Usage

The basic syntax of the else command is as follows:

if (condition) then
    # commands to execute if condition is true
else
    # commands to execute if condition is false
endif

Common Options

The else command itself does not have options, but it is typically used in conjunction with the if statement. The options for the if statement can include various conditions that determine the flow of execution.

Common Examples

Example 1: Simple if-else

set var = 10
if ($var > 5) then
    echo "Variable is greater than 5"
else
    echo "Variable is 5 or less"
endif

Example 2: Checking for a file

set filename = "example.txt"
if (-e $filename) then
    echo "File exists"
else
    echo "File does not exist"
endif

Example 3: User input validation

set user_input = $1
if ("$user_input" == "yes") then
    echo "You agreed!"
else
    echo "You did not agree."
endif

Tips

• Always ensure that the endif statement is included to properly close the if block.
• Use parentheses around conditions for clarity and to avoid syntax errors.
• Combine else with else if for multiple conditional checks to create more complex logic flows.