d2u

d2u [options] file...

-a
    Treat ASCII files as text files.

-b
    Create a backup of the original file.

-c
    Specify the character set to use for conversion. (e.g., iso, 8859, latin, utf8)

-D
    Convert files in subdirectories as well.

-h, --help
    Display a help message.

-i
    In-place conversion (modify the original file).

-q, --quiet
    Be quiet (suppress all warnings).

-s
    Skip binary files.

-v, --verbose
    Be verbose (display progress and warnings).

-z, --convert
    Convert line terminators only (do not change encoding).

The d2u command converts text files created in DOS/Windows format to Unix format. DOS/Windows text files use carriage return (CR) and line feed (LF) characters to mark the end of a line, whereas Unix text files use only a line feed (LF) character. This difference can cause issues when viewing or processing DOS/Windows text files on Unix systems, leading to lines appearing with extra characters (often '^M') or being truncated.

The d2u command removes the carriage return characters from the end of each line in the input file, effectively converting it to Unix format. It can operate on single or multiple files, and provides options for in-place conversion, backup creation, and handling of various character encodings. This is useful for ensuring compatibility between different operating systems when exchanging text-based data. The command can be particularly helpful when dealing with configuration files, scripts, or other text files that originated in a DOS/Windows environment and need to be used on a Unix or Linux system.

The command can corrupt binary files if used improperly. Always back up important files before converting them. The character set option is critical when dealing with files using non-ASCII encodings to avoid data loss or corruption.

The d2u command returns 0 for success, and a non-zero value for errors such as file not found, incorrect arguments, or conversion failures.

It is important to use the correct encoding when converting files. If the encoding is not specified, the default system encoding will be used, which may not be correct for all files. Mismatched encodings can lead to garbled or corrupted text.

The d2u command and its companion u2d (or unix2dos) have been around for a long time, developed to solve the common problem of transferring text files between DOS/Windows and Unix systems. Originally, file transfer protocols didn't always handle line ending conversions automatically. These tools made the conversion simple, even before more sophisticated text editors and integrated development environments became commonplace and offered automatic conversion options.

unix2dos(1), dos2unix(1), tr(1), sed(1)