unexpand

Additional Notes

unexpand converts sequences of spaces into tab characters. It is the inverse of expand. By default it converts leading spaces (at the start of each line) into tabs, but it can also convert spaces within lines at configurable tab stops.

This is useful when you want to reduce file size or conform to a project's tab-based indentation style. It complements expand, which does the reverse (tabs to spaces). Both commands understand the standard 8-column tab stops unless overridden with the -t option.

Syntax

unexpand [options] [file...]

Parameters

• file: One or more files to process. If no file is given, reads standard input.

Common Options

• -a, --all: Convert all sequences of two or more spaces, not just leading whitespace.
• -t N, --tabs N: Set tab stops every N characters (default 8). Can also be a comma-separated list of explicit tab stop positions.
• --first-only: Only convert leading sequences of spaces (default behavior without -a).

Examples

unexpand file.txt

Convert leading spaces to tabs.

unexpand -a file.txt

Convert all space sequences (not just leading) to tabs.

unexpand -t 4 file.txt

Convert spaces assuming 4-column tab stops.

unexpand -t 4,8,12 < input.py

Convert spaces with explicit tab stops at columns 4, 8, and 12.

Practical Notes

• Use unexpand -a to convert in-line alignment spaces (not just indent).
• Paired with expand, this lets you switch between tab and space indentation standards.
• Use cat -A or od -c to verify that tabs were inserted successfully (^I display).
• Many editors have built-in tab/space conversion; unexpand is useful for batch processing.