if-then-else in Bash Scripting - Step-by-Step Execution

Concept Flow - if-then-else

Start

↓

Evaluate condition

↓

Execute THEN block

↓

End

↓

Execute ELSE block

↓

End

The script checks a condition. If true, it runs the THEN part; if false, it runs the ELSE part, then ends.

Execution Sample

Bash Scripting

if [ "$num" -gt 10 ]; then
  echo "Greater than 10"
else
  echo "10 or less"
fi

Checks if variable num is greater than 10 and prints a message accordingly.

Execution Table

Step	Condition	Condition Result	Branch Taken	Output
1	[ "$num" -gt 10 ]	True	THEN	Greater than 10
2	End of if-then-else	-	-	-

💡 Condition true, THEN branch executed, script ends.

Variable Tracker

Variable	Start	After Step 1	Final
num	15	15	15

Key Moments - 2 Insights

Why does the script run the THEN block and not the ELSE block when num is 15?

Because at Step 1 in the execution_table, the condition [ "$num" -gt 10 ] is True, so the THEN branch is taken.

What happens if the condition is false?

If the condition is false, the ELSE block runs instead, as shown in the concept_flow where the No branch leads to ELSE execution.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at Step 1 when num=15?

A Greater than 10

B 10 or less

C No output

D Error

💡 Hint

Check the Output column in execution_table row for Step 1.

At which step does the script decide which branch to take?

A Before Step 1

B Step 2

C Step 1

D After Step 2

💡 Hint

Look at the Condition and Branch Taken columns in execution_table.

If num was 5 instead of 15, which branch would run?

A THEN branch

B ELSE branch

C Both branches

D No branch

💡 Hint

Refer to concept_flow and key_moments about condition false leading to ELSE.

Concept Snapshot

if [ condition ]; then
  # commands if true
else
  # commands if false
fi

Checks condition once.
Runs THEN block if true.
Runs ELSE block if false.
Ends after one branch runs.

Full Transcript

This visual execution shows how a bash if-then-else works. The script starts and evaluates the condition. If the condition is true, it runs the THEN block commands. If false, it runs the ELSE block commands. Then the script ends. For example, if the variable num is 15, the condition checking if num is greater than 10 is true, so the THEN block runs and prints 'Greater than 10'. If num was 5, the ELSE block would run and print '10 or less'. This helps decide between two paths based on a condition.