by Brandon Rhodes • Home

Start all of your commands with a comma

Date: 18 August 2009
Tags:computing

Like many Unix users, I long ago created a ~/bin/ directory in my home directory and added it to my PATH so that I could supplement the wonderfully rich set of basic Unix commands with some conveniences and shell scripts of my own devising.

The problem, of course, was the chance of collision. Because my shell script names tended to be short and pithy collections of lowercase characters, just like the default system commands, there was no telling when Linux would add a new command that would happen to have the same name as one of mine. This was actually not very likely on, say, a System V Revision 3 workstation in the 1980s, but the trouble became quite a bit more acute when I moved into the world of Debian. Red Hat never really worried me, because they packaged (comparatively) so little software. But Debian today supports a huge number of commands; my modest Ubuntu laptop shows several thousand available:

$ apt-file search -x '^/usr/bin/[^/]*$' | wc -l
21733

The solution was obviously to adjust my command names in such a way that they were still easy to type, but would never be chosen as system command names. For me, “easy to type” means not having to use the shift key, and very few characters turned out to be available, unshifted, on a modern keyboard. The lower-case letters are the very characters used in system commands; brackets, backslashes, the colon, the back-tick, and the single-tick all had a special meaning to the shell; and the slash and dot characters both mean something special in a filename. (The slash divides directory names from filenames, and thus cannot appear in a filename itself, while the dot means “hide this file from normal browsing” if it leads the name, and separates a file from its extension in many other cases.)

There was but one character left: the simple, modest comma.

A quick experiment revealed in a flash that the comma was exactly the character that I had been looking for! Every tool and shell that lay in arm's reach treated the comma as a perfectly normal and unobjectionable character in a filename. By simply prefixing each of my custom commands with a comma, they became completely distinct from system commands and thus free from any chance of a collision.

And, best of all, thanks to the magic of tab-completion, it became very easy to browse my entire collection of commands. When trying to remember which of my commands are available in my ~/bin/ directory on a given system, or when simply trying to remember what some of my commands are called, I simply type a comma followed by tab and my list of commands appears:

$ ,«tab»
,complete-scp        ,go-thpgp            ,range
,complete-ssh        ,gr                  ,svn-store-password
,coreoff             ,hss                 ,umount
,coreon              ,mount-thpgp
,find                ,mount-twt

I heartily recommend this technique to anyone with their own ~/bin/ directory who wants their command names kept clean, tidy, and completely orthogonal to any commands that the future might bring to your system. The approach has worked for me for something like a decade, so you should find it immensely robust. And, finally, it's just plain fun.

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