Difference between 'dir' and 'ls' terminal commands?

dir and ls are part of coreutils and dir is almost the same as ls, just with different default options.

The GNU Core Utilities are the basic file, shell and text manipulation utilities of the GNU operating system. These are the core utilities which are expected to exist on every operating system.

info dir says:

dir is equivalent to ls -C -b; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences.

Oh and there is also vdir! info vdir says:

vdir is equivalent to ls -l -b; that is, by default files are listed in long format and special characters are represented by backslash escape sequences.

Most likely dir exists for backwards compatibility or due to historical reasons.

The Relationship Between ls and dir

ls and dir are separate programs that behave similarly. As explained and referenced below, the purpose of dir is to provide a command like ls whose output does not vary depending on whether or not it is going to a terminal. To achieve this helpfully, dir must format its output in a way that is reasonable and useful both for viewing in a terminal and for writing to a file or pipe.

There are two common misconceptions about dir:

• Many people believe dir is an alias of ls, but that is not the case. Neither command is an alias of the other, and by default in Ubuntu, dir is not an alias at all. ls and dir are provided by separate, non-identical executables.
• Many people believe dir exists for obscure historical reasons or to provide compatibility with some standard or some other OS. That is not the case either. ls behaves the way it does for compatibilty. dir, which doesn't have to be compatible because it's not a standard Unix command, behaves in an alternate way that the developers consider valuable in its own right and possibly even preferable.

OK, but exactly how do ls and dir differ?

Both ls and dir list the contents of directories. Two specific differences in their default behaviors distinguish them.

1. When its standard output is a terminal, ls lists filenames in vertically sorted columns (like ls -C). When its standard output is not a terminal (for example, a file or pipe), ls lists filenames one per line (like ls -1).

   Whether or not its standard output is a terminal, dir lists filenames in vertically sorted columns (like ls -C).

   For both ls and dir, these defaults may be overridden by the --format= flag and by the -1, -C, -m, and -x flags, which abbreviate particular --format= options. See 10.1.4 General output formatting in the GNU coreutils reference manual for details.

2. When its standard output is a terminal and a filename to be listed contains control characters, ls prints ? instead of each control character (like ls -q). When its standard output is not a terminal, ls prints control characters as-is (like ls --show-control-chars).

   Whether or not its standard output is a terminal, when dir encounters a control character or any other character that would be interpreted specially if entered into a shell, it prints backslash sequences for the characters. This includes even relatively common characters like spaces. For example, dir will list an entry called Documents backups as Documents\ backups. This is like ls -b.

   For both ls and dir, these defaults may be overridden by the flags listed in 10.1.7 Formatting the file names in the GNU coreutils reference manual. This includes -b, -q, --quoting-style=, and some others.

Sources: ls invocation and dir invocation, in the GNU coreutils reference manual.

Why have dir?

The rationale for a separate dir utility is given in 4.5 Standards for Interfaces Generally of the GNU coding standards. I recommend reading that whole section to understand the developers' reasoning, but here are the highlights as applicable to ls/dir:

Please don’t make the behavior of a utility depend on the name used to invoke it....

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 a command-line program depend on the type of output device....

Compatibility requires certain programs to depend on the type of output device. It would be disastrous if ls or 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 like ls except that its default output format is always multi-column format.

The GNU Project considers it undesirable, from a technical perspective, for a utility to produce different output depending on what kind of device it is writing to (at least in the utility's default configuration). For some utilities, including ls, device-dependent output is necessary for compatibility and so it works the way users expect. Some users do also specifically prefer this device-dependent behavior.

While ls could not reasonably be written to behave device independently, a separate dir utility was created to achieve this. Thus dir is not the utility that behaves strangely for reasons of historical compatibility--ls is.

^{To see how ls, dir, and the related vdir utility are implemented in the coreutils source code without needless code duplication, see ls-dir.c, ls-ls.c, ls-vdir.c, ls.h, and ls.c.}

Is dir really useful?

If you've ever wished ls produced multi-column output even when you piped it to less (ls | less) or redirected it to a file (ls > out.txt), you can use dir or ls -C.

If you've ever wished you could directly copy a filename shown by ls and use it as part of a command without worrying about quoting, you can use dir or ls -b.

dir is equivalent to ls -Cb, so in that sense you don't need dir. But dir provides a combination of options that in practice is often useful (though not widely known about).

Why do I get colorized output from ls (even ls -Cb) but not dir?!

Most Ubuntu users have an alias called ls which runs ls --color=auto. When ls exists both as an alias and an external command, the alias takes precedence in simple, interactive commands.

^{Alias definitions aren't expanded recursively--it's the external ls command that the ls alias is calling with --color=auto. See 6.6 Aliases in the Bash reference manual for more information on how aliases work.}

When passed to ls, dir, or vdir (and some other commands, like grep), --color=auto uses color when its output is a terminal, but not otherwise.

By default in Ubuntu, user accounts are created with this in ~/.bashrc:

# enable color support of ls and also add handy aliases
if [ -x /usr/bin/dircolors ]; then
    test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
    alias ls='ls --color=auto'
    #alias dir='dir --color=auto'
    #alias vdir='vdir --color=auto'

    alias grep='grep --color=auto'
    alias fgrep='fgrep --color=auto'
    alias egrep='egrep --color=auto'
fi

You'll notice the ls alias (alias ls='ls --color=auto') is uncommented, while those for dir and vdir are commented out with # so they take no effect. That is, while dir is not an alias, ls is (but not to dir).

How do I make dir produce colored output, too?

To enable colored output with dir, simply edit .bashrc in your home directory and uncomment the #alias dir='dir --color=auto' line by removing the leading #. In shells started after the change, dir will be an alias.

^{If you want the change in the current shell, you can run the alias definition as a command, or you can source .bashrc by running . ~/.bashrc.}

This arguably goes against the main point of dir--that it should produce the same sort of output regardless of the output device. However:

• If you find it useful to make this dir alias, you should certainly do so.
• When called as an external command, for example in scripts or if you override the alias by running \dir or command dir, dir will still produce device-independent output. This is to say that aliasing dir to dir --color=auto does not really break dir.

I would be inclined to think that dir is there just for backwards compatibility.

From GNU Coreutils:

dir is equivalent to ls -C -b; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences.

By the way, ls doesn't colorize the output by default: this is because most distros alias ls to ls --color=auto in /etc/profile.d. For a test, type unalias ls then try ls: it will be colorless.

Source: Renan's answer to What's the difference between “dir” and “ls”?