if-then-fi structure in Bash Scripting - Step-by-Step Execution

Concept Flow - if-then-fi structure

Start

↓

Evaluate condition

↓

Execute commands inside then

↓

End if

↓

Skip commands inside then

↓

End if

The script checks a condition. If true, it runs commands inside then. If false, it skips them and ends the if block.

Execution Sample

Bash Scripting

if [ "$num" -gt 0 ]; then
  echo "Positive number"
fi

Checks if num is greater than 0; if yes, prints 'Positive number'.

Execution Table

Step	Condition	Result	Branch Taken	Output
1	[ "$num" -gt 0 ]	True	Execute then block	Positive number
2	End of if	-	Exit if	-

💡 Condition false or commands inside then executed; if block ends with fi.

Variable Tracker

Variable	Start	After Step 1	Final
num	5	5	5

Key Moments - 2 Insights

Why does the script skip the echo command sometimes?

Because the condition in the if statement is false, so the then block is not executed (see execution_table step 1).

What does 'fi' mean in the script?

'fi' marks the end of the if block, telling the shell where the conditional commands finish.

Visual Quiz - 3 Questions

Look at the execution table, what happens when the condition is true?

A The commands inside then block are skipped

B The commands inside then block run

C The script ends immediately

D The condition is checked again

💡 Hint

See execution_table row 1, 'Branch Taken' and 'Output' columns

At which step does the script finish the if block?

A Step 2

B Step 1

C Before Step 1

D After Step 2

💡 Hint

Check execution_table row 2, 'Step' and 'Branch Taken' columns

If num was -3, what would happen at step 1?

A Condition true, then block runs

B Script crashes

C Condition false, then block skipped

D Condition true, but then block skipped

💡 Hint

Refer to variable_tracker for num value and execution_table step 1 condition result

Concept Snapshot

if-then-fi structure in bash:
if [ condition ]; then
  commands
fi
- Checks condition
- Runs commands if true
- Ends with fi
- Skips commands if false

Full Transcript

This visual execution shows how the bash if-then-fi structure works. The script starts by evaluating a condition inside the if statement. If the condition is true, it executes the commands inside the then block. If false, it skips those commands. The if block ends with fi. Variables like num keep their values unchanged during this process. Key points include understanding that fi marks the end of the if block and that commands inside then only run when the condition is true. The execution table traces these steps clearly, showing when commands run or are skipped.