Problems with Hyphens in Functions, Aliases, and Executables

bashcshkshshellzsh

In my testing (in Bash and Z Shell), I saw no problems with defining functions or aliases or executable shell scripts which have hyphens in the name, but I'm not confident that this will be okay in all shells and in all use cases.

The reason I would like to do this is that a hyphen is easier to type than an underscore, and therefore faster and smoother.

One reason I'm hesitant to trust that it's not a problem is that in some languages (Ruby for example) the hyphen would be interpreted as a minus sign even without spaces around it. It wouldn't surprise me if something like this might happen in some shells, where the hyphen is interpreted as signaling an option even without a space.

Another reason I'm a little suspicious is that my text editor screws up the syntax highlighting for functions with hyphens. (But of course it's entirely possible that that's just a bug in its syntax highlighting configuration for shell scripts.)

Is there any reason to avoid hyphens?

Best Answer

POSIX and Hyphens: No Guarantee

According to the POSIX standard, a function name must be a valid name and a name can consist of:

3.231 Name
In the shell command language, a word consisting solely of underscores, digits, and alphabetics from the portable character set. The first character of a name is not a digit.

Additionally, an alias must be a valid alias name, which can consist of:

3.10 Alias Name
In the shell command language, a word consisting solely of underscores, digits, and alphabetics from the portable character set and any of the following characters: '!', '%', ',', '@'.

Implementations may allow other characters within alias names as an extension. (Emphasis mine.)

A hyphen is not listed among the characters that must be allowed in either case. So, if they are used, portability is not guaranteed.

Examples of Shells That Do Not Support Hyphens

dash is the default shell (/bin/sh) on the debian-ubuntu family and it does not support hyphens in function names:

$ a-b() { date; }
dash: 1: Syntax error: Bad function name

Interestingly enough, it does support hyphens in aliases, though, as noted above, this is an implementation characteristic, not a requirement:

$ a_b() { printf "hello %s\n" "$1"; }
$ alias a-b='a_b'
$ a-b world
hello world

The busybox shell (Almquist shell) also does not support hyphens in function names:

$ a-b() { date; }
-sh: Syntax error: Bad function name

Summary of Hyphen Support by Shell

The following shells are known to support hyphens in function names:

  • ksh, bash, zsh

The following shells are known not to support hyphens in function names:

  • ash (busybox), csh, tcsh, dash

Conclusions

  • Hyphens are non-standard. Stay away from them if you want cross-shell compatibility.
  • Use underscores instead of hyphens: underscores are accepted everywhere.
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