Please don't make the behavior of a utility depend on the name used to invoke it. It is useful sometimes to make a link to a utility with a different name, and that should not change what it does.
Instead, use a run time option or a compilation switch or both to select among the alternate behaviors.
Likewise, please don't make the behavior of the program depend on the type of output device it is used with. Device independence is an important principle of the system's design; do not compromise it merely to save someone from typing an option now and then. (Variation in error message syntax when using a terminal is ok, because that is a side issue that people do not depend on.)
If you think one behavior is most useful when the output is to a terminal, and another is most useful when the output is a file or a pipe, then it is usually best to make the default behavior the one that is useful with output to a terminal, and have an option for the other behavior.
Compatibility requires certain programs to depend on the type of output
device. It would be disastrous if
sh did not do so
in the way all users expect. In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type. For example, we provide a
dir program much
ls except that its default output format is always
It is a good idea to follow the POSIX guidelines for the
command-line options of a program. The easiest way to do this is to use
getopt to parse them. Note that the GNU version of
will normally permit options anywhere among the arguments unless the
special argument `--' is used. This is not what POSIX
specifies; it is a GNU extension.
Please define long-named options that are equivalent to the
single-letter Unix-style options. We hope to make GNU more user
friendly this way. This is easy to do with the GNU function
One of the advantages of long-named options is that they can be consistent from program to program. For example, users should be able to expect the "verbose" option of any GNU program which has one, to be spelled precisely `--verbose'. To achieve this uniformity, look at the table of common long-option names when you choose the option names for your program (see section Table of Long Options).
It is usually a good idea for file names given as ordinary arguments to be input files only; any output files would be specified using options (preferably `-o' or `--output'). Even if you allow an output file name as an ordinary argument for compatibility, try to provide an option as another way to specify it. This will lead to more consistency among GNU utilities, and fewer idiosyncracies for users to remember.
All programs should support two standard options: `--version' and `--help'.
GNU Emacs 19.30The program's name should be a constant string; don't compute it from
argv. The idea is to state the standard or canonical name for the program, not its file name. There are other ways to find out the precise file name where a command is found in
PATH. If the program is a subsidiary part of a larger package, mention the package name in parentheses, like this:
emacsserver (GNU Emacs) 19.30If the package has a version number which is different from this program's version number, you can mention the package version number just before the close-parenthesis. If you need to mention the version numbers of libraries which are distributed separately from the package which contains this program, you can do so by printing an additional line of version info for each library you want to mention. Use the same format for these lines as for the first line. Please do not mention all of the libraries that the program uses "just for completeness"---that would produce a lot of unhelpful clutter. Please mention library version numbers only if you find in practice that they are very important to you in debugging. The following line, after the version number line or lines, should be a copyright notice. If more than one copyright notice is called for, put each on a separate line. Next should follow a brief statement that the program is free software, and that users are free to copy and change it on certain conditions. If the program is covered by the GNU GPL, say so here. Also mention that there is no warranty, to the extent permitted by law. It is ok to finish the output with a list of the major authors of the program, as a way of giving credit. Here's an example of output that follows these rules:
GNU Emacs 19.34.5 Copyright (C) 1996 Free Software Foundation, Inc. GNU Emacs comes with NO WARRANTY, to the extent permitted by law. You may redistribute copies of GNU Emacs under the terms of the GNU General Public License. For more information about these matters, see the files named COPYING.You should adapt this to your program, of course, filling in the proper year, copyright holder, name of program, and the references to distribution terms, and changing the rest of the wording as necessary. This copyright notice only needs to mention the most recent year in which changes were made--there's no need to list the years for previous versions' changes. You don't have to mention the name of the program in these notices, if that is inconvenient, since it appeared in the first line.
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