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

Concept Flow - if-elif-else

Start

↓

Check if condition1

|Yes↓

Execute block1

↓

End

No↓

Check if condition2

|Yes↓

Execute block2

↓

End

No↓

Execute else block

↓

End

The script checks the first condition; if true, it runs its block and ends. Otherwise, it checks the next condition(s). If none match, it runs the else block.

Execution Sample

Bash Scripting

num=7
if [ $num -lt 5 ]; then
  echo "Less than 5"
elif [ $num -eq 7 ]; then
  echo "Equal to 7"
else
  echo "Other number"
fi

This script checks if num is less than 5, equal to 7, or something else, then prints a message.

Execution Table

Step	Condition Checked	Condition Result	Branch Taken	Output
1	[ $num -lt 5 ]	False	No
2	[ $num -eq 7 ]	True	Yes	Equal to 7
3	else	N/A	No

💡 Condition [ $num -eq 7 ] is True, so the elif block runs and script ends.

Variable Tracker

Variable	Start	After Execution
num	7	7

Key Moments - 2 Insights

Why does the script not print "Less than 5" even though it checks that condition first?

Because the condition [ $num -lt 5 ] is False (num is 7), so the script skips that block and checks the next condition as shown in step 1 and 2 of the execution_table.

What happens if none of the if or elif conditions are true?

The else block runs, as it is the fallback. This is shown in step 3 of the execution_table where else would execute if previous conditions were False.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A Equal to 7

B Less than 5

C Other number

D No output

💡 Hint

Check the 'Output' column in row for step 2 in execution_table.

At which step does the script decide to run the elif block?

A Step 1

B Step 2

C Step 3

D Never

💡 Hint

Look at the 'Branch Taken' column and see where condition is True for elif.

If num was 3, how would the execution table change?

A Step 2 condition True, output 'Equal to 7'

B Step 3 else runs

C Step 1 condition True, output 'Less than 5', no further checks

D No output at all

💡 Hint

Refer to variable_tracker and imagine num=3, then check condition results in execution_table.

Concept Snapshot

if-elif-else in bash:
if [ condition1 ]; then
  commands
elif [ condition2 ]; then
  commands
else
  commands
fi

Checks conditions in order; runs first true block; else runs if none true.

Full Transcript

This visual execution shows how bash if-elif-else works. The script starts by checking the first condition. If it is true, it runs that block and ends. If false, it checks the next condition. If none are true, it runs the else block. In the example, num=7 is checked against less than 5 (false), then equal to 7 (true), so it prints 'Equal to 7' and stops. Variables stay the same during checks. This helps beginners see exactly how conditions are tested and which block runs.