String suffix removal (${var%pattern}) in Bash Scripting - Step-by-Step Execution

Concept Flow - String suffix removal (${var%pattern})

Start with variable var

↓

Apply suffix pattern match

↓

Remove shortest matching suffix

↓

Return modified string

↓

End

The shell checks the variable's value, finds the shortest suffix matching the pattern, removes it, and returns the result.

Execution Sample

Bash Scripting

filename="report.txt"
result=${filename%.txt}
echo "$result"

Removes the shortest suffix '.txt' from the variable 'filename' and prints the result.

Execution Table

Step	Variable 'filename'	Pattern	Action	Resulting Value	Output
1	report.txt	%.txt	Check if suffix '.txt' matches	Matches suffix '.txt'
2	report.txt	%.txt	Remove shortest matching suffix '.txt'	report
3	report	N/A	Echo the result	N/A	report
4	report	N/A	End of script	N/A

💡 Suffix '.txt' removed; no more matches; script ends.

Variable Tracker

Variable	Start	After suffix removal	Final
filename	report.txt	report.txt	report.txt
result	N/A	report	report

Key Moments - 2 Insights

Why does only the shortest suffix matching the pattern get removed?

Because the '%' operator removes the shortest suffix matching the pattern, as shown in execution_table step 2 where only '.txt' is removed, not more.

What happens if the pattern does not match the suffix?

No removal happens; the variable stays the same. This is implied because the action only removes when a match is found (step 1 and 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'result' after suffix removal?

A .txt

B report

C report.txt

D report.tx

💡 Hint

Check execution_table row 2 under 'Resulting Value' column.

At which step does the script output the final result?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table row 3 under 'Output' column.

If the variable was 'archive.tar.gz' and pattern was '%.gz', what would be the result after removal?

A archive.tar

B archive

C archive.tar.gz

D tar.gz

💡 Hint

Remember '%' removes shortest matching suffix; see concept_flow and execution_table logic.

Concept Snapshot

Syntax: ${var%pattern}
Removes shortest suffix matching pattern from var's value.
Useful to strip file extensions or suffixes.
Only removes if pattern matches suffix.
Does not change original variable unless reassigned.

Full Transcript

This example shows how to remove a suffix from a string variable in bash using ${var%pattern}. The shell looks at the variable's value, finds the shortest suffix matching the pattern, removes it, and returns the modified string. For example, with filename="report.txt" and pattern '%.txt', the suffix '.txt' is removed, resulting in 'report'. The script then echoes this result. If the pattern does not match, the string remains unchanged. This is a simple way to strip file extensions or other suffixes in bash scripting.