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Introduction to conditional statement (If)

Sometimes, you need to take different action depending on the success or failure of a command. The if statement helps you in such conditions.

Syntax

if [ condition ]
then 
    statements 1
    statements 2
    .
    .
    statements n
fi

if [[ condition ]]
then 
    statements 1
    statements 2
    .
    .
    statements n
fi
The condition is true or returns 0 (zero), the statements get executed.

NOTE:

  1. There should be a space with in square brackets at starting and ending. space Picture courtesy: https://kodekloud.com/

    Example if [[ 5 -gt 0 ]]

  2. The condition often involves numerical or string comparison tests.

  3. The condition returns a status of zero when it succeeds and some other status when it fails.
  4. The condition may be a command (e.g if [ $(whoami) = "root" ])
  5. Unary expressions are often used to examine the status of a file