Shell Programming and Scripting

@alister
Very good explanation and example.

If it can be explained by a simple change of environment that's brilliant. I'd forgotten about certain Linux using UTF-8 and some of the other consequences like really slow sort, grep, sed etc. . There are many advantages of UTF-8/UTF-16/UTF-nn in the Word Processing world but I can't see any advantage on the default command line.

As you will all know I'm a bit of a Posix cynic (though I support the Posix ideal) mainly because I come across too many non-compliant situations. I have lost track of the "current Posix standard" (despite @jlliagre's best efforts).

I'm not sure that the Original Post is 100% one of those situations because the O/P noticed that what I believed was the portable syntax worked. The Linux/BSD amomaly with the treatment of quoted square brackets in the tr command is in my opinion a coding error.


Not sure if that quote in context because this is nothing to do with Escape Sequences (like for Printer control). If it is, then IMHO that Posix standard needs urgent correction. It's universally expected in unix syntax that a character which is part of the syntax of a command must be escaped if it is to be considered as data.

Hehehe. Understandable. You may enjoy standards

I try to keep up with POSIX enough to know when I'm using an extension, but that's about it. Most of the time, when I dig into it, it's a result of investigating some oddity in one of this forum's threads.


As far as POSIX tr is concerned, the brackets are not special so they do not require a backslash escape sequence. Real world implementations probably drop the backslash and treat the following square-bracket literally, as your implementation is doing (although in your case it's by necessity since it's trying to accomodate the historical syntax), but doing so isn't required by POSIX. A compliant implementation of tr could choose to abort with an error when it encounters \[ or \].

Regards,
Alister

Sorry, not going to click on standards because the URL looks dubious.

How a Posix verson of tr is going to see \[ \] beats me? The Shell gets there first and eats the backslash.

Anyway, I think that this is yet another Posix mistake and we will have to code round it.

Please don't blame POSIX for your misunderstanding of single quotes:

Code:

$ echo '\[\]'
\[\]

$ echo '\\'
\\

$