Are there any single character bash aliases to be avoided?

Question

Often I find my self making single character aliases, because after all, they exist to save input time. I'm curious if this should be avoided. I do not know of any conflicts.

Answer 1

Things to avoid:

• standard or common commands with single character names: w (show logged in users' activity), X (X Window System server), R (R programming language interpreter), [ (similar to test)
• builtins of your shell or of common shells: [, ., :, -, r
• shell keywords: {, }, !
• ? and * wildcard characters
• special characters in the shell syntax: `"$&();'#~|\<>, (also ^, % in some shells), SPC, TAB, NL (and other blanks with some shells)
• better avoid non-ASCII characters (as those have different encoding depending on the locale)
• better avoid control characters (beside TAB and NL already mentioned above) as they're not that easy to enter, and depending on context, not always visible, or with different representations. Only zsh will let you define and use an alias for the NUL character. bash lets you define an alias for ^A (the control character with byte value 1) but not use it apparently.

To find commands with single character names:

• bash: compgen -c | grep -x . | sort -u (also includes keywords, assumes command names don't contain newline characters)

• zsh: type -m '?' (or type -pm '?' if you don't want functions/aliases/builtins/keywords).

• Debian or derivatives: to find any command in any package with single character name:

  $ apt-file find -x '/s?bin/.$'
  coreutils: /usr/bin/[
  e-wrapper: /usr/bin/e
  python3-q-text-as-data: /usr/bin/q
  r-base-core: /usr/bin/R
  r-base-core: /usr/lib/R/bin/R
  r-cran-littler: /usr/bin/r
  r-cran-littler: /usr/lib/R/site-library/littler/bin/r
  wims: /var/lib/wims/public_html/bin/c
  xserver-xorg-core: /usr/bin/X
  

Answer 2

The simplest way is probably to check whether something with that name already exists. On my system:

$ for char in {A..z}; do type "$char" 2>/dev/null; done
R is /usr/bin/R
X is /usr/bin/X
[ is a shell builtin
l is aliased to `ls -CF'
w is /usr/bin/w

As far as I know this shows all relevant collisions:

• Other aliases like l
• Shell reserved words
• Functions
• Shell builtins
• File commands such as w and [

Answer 3

Addressing: "I'm curious if this should be avoided."

As described in the other answers, there should be no technical problem as long as the command you are overriding with the alias it isn't something you are going to use.

The main frustration with using aliases like this is when you are helping a friend or ssh into a computer where you haven't copied your .bashrc yet. All of the muscle memory you've developed makes you feel like a fish out of water. I find it so disorienting that I try to keep my aliases to a minimum.

Answer 4

I'm curious if this should be avoided. I do not know of any conflicts.

It doesn't really matter for conflicts you don't already know about.

Aliases are an interactive shell configuration. They're not active in scripts. If you define an alias with the same name as an existing program, all it means is that when you personally type it in the shell, you'll by default call your alias instead of the other program. Other programs won't see your alias, so there is no conflict.

As an example, if you don't know the command X or never plan to call it directly from the shell, it's not really an issue if you define an alias X. When another program like startx/xinit call X they won't see your alias, so there won't be a conflict.

Answer 5

It depends on what you user aliases for (eg. how big of an issue it is if you execute wrong alias by mistake), and how often you make mistakes.

For example:

• using r='rm -rf *' and t='ls -l *tar*' is probably a very bad idea, even if you seldom press wrong key.
• using r='file *.png | grep RGB' and t='ls -l *tar*' is probably not a problem.

In later case, if you type r instead of (close on keyboard, and thus easy to wrongly type) t, you'd just get output which you didn't want, and you can easily type correct alias. In former case however, if you type r instead of t, you will do unwanted damage.

So the point is: if you do one-letter aliases, use them only for read-only things (and not for things that may change data in a way that would cause you problems if run inadvertently)

Answer 6

This bash one liner will show you all the commands which are a single character (I'm not a bash professional, so probably this script is not the most elegant):

echo $PATH |
    sed 's/:/\n/g' |
    while read p; do ls "$p" 2>/dev/null; done |
    egrep "^.$" |
    sort -u

On Fedora 33 I get:

[
w
X