Brace expansion ({1..10}) in Bash Scripting - Step-by-Step Execution

Concept Flow - Brace expansion ({1..10})

Start

↓

Detect brace expansion

↓

Parse range start and end

↓

Generate sequence from start to end

↓

Replace brace with sequence

↓

Output expanded list

↓

End

Brace expansion detects the {start..end} pattern, generates the sequence, and outputs the expanded list.

Execution Sample

Bash Scripting

echo {1..5}

This command expands the brace {1..5} into the sequence 1 2 3 4 5 and prints it.

Execution Table

Step	Action	Input	Output
1	Detect brace expansion	echo {1..5}	{1..5} detected
2	Parse range	{1..5}	start=1, end=5
3	Generate sequence	start=1, end=5	1 2 3 4 5
4	Replace brace with sequence	echo {1..5}	echo 1 2 3 4 5
5	Execute command	echo 1 2 3 4 5	1 2 3 4 5

💡 Sequence generated and printed, expansion complete

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
input_string	echo {1..5}	echo {1..5}	echo 1 2 3 4 5	echo 1 2 3 4 5
start	N/A	1	1	1
end	N/A	5	5	5
sequence	N/A	N/A	1 2 3 4 5	1 2 3 4 5

Key Moments - 2 Insights

Why does the command output multiple numbers separated by spaces instead of the literal {1..5}?

Because brace expansion replaces the {1..5} with the sequence 1 2 3 4 5 before the command runs, as shown in step 4 of the execution table.

What happens if the start number is greater than the end number, like {5..1}?

Brace expansion generates a descending sequence from 5 down to 1, similar to step 3 but counting backwards.

Visual Quiz - 3 Questions

Look at the execution table, what is the output after step 3?

A 1 2 3 4 5

B {1..5}

C echo 1 2 3 4 5

D echo {1..5}

💡 Hint

Check the 'Output' column in row for step 3 in the execution table.

At which step is the brace replaced with the sequence?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look for the step where the input changes from 'echo {1..5}' to 'echo 1 2 3 4 5' in the execution table.

If the range was {3..7}, what would be the sequence generated at step 3?

A 7 6 5 4 3

B 1 2 3 4 5

C 3 4 5 6 7

D 3 7

💡 Hint

Refer to the variable_tracker for how the sequence is generated from start to end.

Concept Snapshot

Brace expansion syntax: {start..end}
Generates a sequence of numbers from start to end.
Replaces the brace with the full sequence before command runs.
Supports ascending and descending ranges.
Example: echo {1..5} outputs '1 2 3 4 5'.

Full Transcript

Brace expansion in bash scripting detects patterns like {1..10} and expands them into a sequence of numbers. The shell first detects the brace, then parses the start and end numbers. It generates the full sequence from start to end, replacing the brace with this sequence. Finally, the command runs with the expanded list. For example, 'echo {1..5}' becomes 'echo 1 2 3 4 5' and prints the numbers. This process allows quick generation of sequences without loops or manual typing.