znew

Additional Notes

znew recompresses files from the old Unix compress format (.Z) to the gzip format (.gz). It decompresses the .Z file and recompresses it with gzip, which typically achieves better compression ratios. The original .Z file can be optionally removed after conversion.

This tool was useful during the transition from compress to gzip. It is rarely needed today since .Z files are uncommon. The conversion preserves the file's timestamp and mode.

Syntax

znew [options] file[.Z]...

Parameters

• file: One or more .Z files to convert.

Common Options

• -f, --force: Force conversion even if a .gz file already exists.
• -t, --test: Test the integrity of the new .gz file before removing the original.
• -v, --verbose: Show compression ratios and progress.
• -9: Use maximum compression level.
• -K, --keep: Keep the original .Z file (do not remove after conversion).
• -P, --small: Use the smallest possible memory level (slower but less memory).

Examples

znew file.Z

Convert file.Z to file.gz and remove file.Z.

znew -K file.Z

Convert file.Z to file.gz but keep the original.

znew -v -9 file.Z

Convert with maximum compression and show verbose output.

znew -t *.Z

Convert all .Z files and test each new .gz before removing originals.

Practical Notes

• If the resulting .gz file is not smaller, the conversion is skipped (unless -f is used).
• The -t flag is recommended to ensure data integrity before the original is removed.
• Modern systems usually have gunzip which can decompress both .Z and .gz directly, making explicit conversion unnecessary.
• Use zcat to read either format without conversion.