u2d

u2d [OPTION]... [FILE]...
u2d [OPTION]... -n INFILE OUTFILE...

FILE...
    Specifies one or more input files to be converted. If no files are specified, u2d reads from standard input and writes to standard output.

-k, --keepdate
    Keeps the original modification date of the converted file. Without this option, the file's modification date will be updated to the time of conversion.

-o, --oldfile
    This is the default behavior. It converts the file in place, overwriting the original file with the converted content.

-n, --newfile
    Converts the input file(s) and writes the output to new file(s). This option requires pairs of input and output filenames (INFILE OUTFILE).

-s, --safe
    Skips conversion of files that appear to be binary files. This prevents accidental corruption of non-textual data.

-F, --force
    Forces conversion even if the file appears to be binary. Use with caution, as this can corrupt non-text files.

-q, --quiet
    Suppresses all warning messages and informational output.

-v, --verbose
    Prints detailed information during the conversion process, such as the names of files being processed.

-h, --help
    Displays a help message with usage instructions and exits.

-V, --version
    Outputs version information about the u2d utility and exits.

The u2d (Unix to DOS) command is a utility primarily used to convert text files that utilize Unix-style line endings (represented by a single newline character, \n) to DOS/Windows-style line endings (which consist of a carriage return followed by a newline character, \r\n). This conversion is essential when transferring text files between Unix-like operating systems (Linux, macOS, BSD) and Windows, as incompatible line endings can lead to display issues in text editors, incorrect parsing by scripts, or malfunctions in applications.

While u2d itself might often be a custom script, an alias, or a symbolic link, its core functionality mirrors that of the more widely recognized unix2dos command. It operates by scanning the input file, identifying each instance of a Unix newline character, and then inserting a carriage return character immediately before it. This process makes the file compatible with applications and systems that expect the CRLF line ending convention.

This command is particularly valuable in cross-platform development environments, during data migration, or when sharing plain text data where line ending consistency is critical for proper interpretation and display.

The u2d command is not a standard utility across all Linux distributions and may not be installed by default. Its availability, exact behavior, and available options can vary significantly. Users might find it implemented as a custom shell script, an alias, or a symbolic link to the more common unix2dos command.

Using u2d (or any line ending conversion tool) on binary files will almost certainly corrupt them. Always ensure you are converting plain text files. If unsure, use the -s (safe) option if available, or back up files before performing any in-place conversions.

The fundamental operation of u2d involves iterating through the input file's content and, for every Unix-style newline character (\n) encountered, prepending it with a carriage return character (\r). This transforms LF into CRLF, making the file correctly formatted for DOS/Windows applications.

Like many Unix utilities, if no specific input FILE is provided, u2d typically reads from standard input (stdin) and writes the converted content to standard output (stdout). This allows it to be effectively used within command pipelines. For instance, to convert a file from stdin and redirect its output to a new file: cat unix_file.txt | u2d > dos_file.txt.

The need for line ending conversion utilities like u2d arose from the early divergence in operating system conventions. Unix-like systems adopted the single Line Feed (\n) character to denote a new line, while DOS and later Windows systems opted for a Carriage Return followed by a Line Feed (\r\n). This difference often led to files created on one system appearing as a single long line or with extra characters when opened on another.

To bridge this incompatibility, utilities were developed to convert between these formats. While u2d itself might be a more recent or custom wrapper, the underlying functionality, embodied by commands like unix2dos, has been a staple in cross-platform computing for decades. These tools ensure seamless file exchange and compatibility, making them indispensable for developers and users working in mixed-OS environments.

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