[Unix] C Shell (csh) if: Conditional execution of commands

Overview

The if command in C Shell (csh) is used to execute commands based on the evaluation of a condition. It allows scripts to make decisions and perform different actions depending on whether certain conditions are true or false.

Usage

The basic syntax of the if command is as follows:

if (condition) then
    command1
else
    command2
endif

Common Options

• then: Indicates the start of the commands to be executed if the condition is true.
• else: Specifies the commands to be executed if the condition is false.
• endif: Marks the end of the if statement.

Common Examples

Example 1: Simple Condition Check

Check if a file exists and print a message accordingly.

if (-e myfile.txt) then
    echo "File exists."
else
    echo "File does not exist."
endif

Example 2: Numeric Comparison

Compare two numbers and print which one is greater.

set num1 = 10
set num2 = 20

if ($num1 > $num2) then
    echo "$num1 is greater than $num2."
else
    echo "$num2 is greater than or equal to $num1."
endif

Example 3: String Comparison

Check if two strings are equal.

set str1 = "hello"
set str2 = "world"

if ("$str1" == "$str2") then
    echo "Strings are equal."
else
    echo "Strings are not equal."
endif

Tips

• Always ensure that conditions are enclosed in parentheses.
• Use proper indentation for better readability of nested if statements.
• Remember to use endif to close the if block; otherwise, you may encounter syntax errors.