pnmalias

Perform antialiasing on a PNM image, taking black pixels as background and white pixels as foreground

$ pnmalias [path/to/input.pnm] > [path/to/output.ppm]

$ pnmalias -bcolor [background_color] -fcolor [foreground_color] [path/to/input.pnm] > [path/to/output.ppm]

$ pnmalias [[-fo|-fonly]] [path/to/input.pnm] > [path/to/output.ppm]

$ pnmalias [[-ba|-balias]] [path/to/input.pnm] > [path/to/output.ppm]

pnmalias [-a alias program arguments] [-d alias] [-f aliasfile] [-l] [-v]

-a alias program arguments
    Adds or changes an alias. alias is the new command name, program is the Netpbm utility (e.g., anytoppm), and arguments are the default parameters for that program.

-d alias
    Deletes the specified alias from the configuration file.

-f aliasfile
    Specifies an alternative configuration file to use instead of the default .pnmalias.

-l
    Lists all currently defined aliases and their corresponding commands.

-v
    Enables verbose output, showing more details about the operations being performed by pnmalias.

pnmalias is a utility from the Netpbm suite designed to manage aliases for programs that convert to and from the Portable Anymap (PNM) format. It allows users to define custom, more descriptive command names (e.g., "giftoppm", "jpegtopnm") that map to the generic anytoppm or ppmtoany commands with specific format arguments. This simplifies command-line usage by abstracting away the need to remember the exact syntax for each conversion.

The tool can add, delete, or list these aliases, typically by modifying a configuration file (often .pnmalias in the user's home directory). When a program like anytoppm is invoked with an alias, it interprets the alias to determine the desired input format. This makes the Netpbm toolkit more user-friendly for common image format conversions, allowing users to invoke specific conversions with intuitive command names without remembering the underlying generic command arguments.

Aliases defined by pnmalias are only recognized by specific Netpbm programs like anytoppm and ppmtoany; they are not shell aliases.
Changes made by pnmalias are persistent, modifying the specified alias file, which can affect all subsequent Netpbm operations relying on those aliases.
Ensure the aliased program (e.g., anytoppm) is correctly installed and accessible via the system's PATH for the aliases to function as intended when invoked.

By default, pnmalias looks for and modifies an alias file named .pnmalias in the user's home directory ($HOME/.pnmalias). If this file doesn't exist, pnmalias will create it upon adding the first alias, ensuring user-specific alias configurations are maintained.

The .pnmalias file is a plain text file where each line defines an alias. The format is typically: alias_name program_name arguments. For example, a line like giftoppm anytoppm gif defines an alias named 'giftoppm' that calls 'anytoppm' with the argument 'gif'.

The aliases themselves are not executable commands. Instead, when you attempt to run a command like giftoppm, if it's not found as a direct executable, the Netpbm anytoppm or ppmtoany programs are designed to check if the invoked command name (e.g., giftoppm) matches an alias defined in the .pnmalias file. If a match is found, they then execute themselves with the corresponding arguments specified by the alias (e.g., anytoppm gif), effectively performing the desired conversion.

pnmalias is an integral part of the Netpbm project, which evolved from the Pbmplus package in the early 1990s. Its development was driven by the need to simplify the command-line interface for the vast array of image format converters within the Netpbm suite. Instead of requiring users to always specify input/output formats explicitly with generic tools like anytoppm, pnmalias enabled the creation of user-friendly wrappers (e.g., giftoppm) that automatically passed the correct format arguments, significantly improving usability and reducing typing for common conversions. It reflects a design philosophy aimed at making powerful command-line tools more accessible.

pnm(5), anytoppm(1), ppmtoany(1), netpbm(1)