On Tue, Jun 13, 2023 at 2:43 PM Jonathan Tan <jonathantanmy@xxxxxxxxxx> wrote:
> Eric Sunshine <sunshine@xxxxxxxxxxxxxx> writes:
> > On Tue, Jun 13, 2023 at 1:44 PM Jonathan Tan <jonathantanmy@xxxxxxxxxx> wrote:
> > > + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
> > > + "\xc2\xa2"), as the latter is not portable.
> >
> > The shell itself doesn't interpret these sequences, so this
> > description feels too generic. Perhaps it would make more sense to
> > cite specific tools for which octal sequences are needed for
> > portability reasons, such as `printf`, `sed`, `tr`, etc.
>
> Ah...good point. I checked with "echo" in "dash" and assumed that it
> was "dash" that was interpreting the escapes, but indeed it is the
> "echo" (and "printf") builtins in "dash" that are actually interpreting
> them. What do you think of the following in the commit message:
>
> Hexadecimal escapes in shell scripts are not portable across shell builtins (in
> particular, the "printf" of "dash" does not support them). Write in the CodingGuidelines
> document that we should be using octal escapes instead.
>
> and in the CodingGuidelines doc:
>
> + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
> + "\xc2\xa2"), as the latter is not portable across some shell builtins like printf.
The portability concern is not specific to a certain shell or whether
a command is builtin, so it feels misleading to single out "dash" and
builtins. The same portability problems can crop up, as well, with
older (non-"dash") shells, and with commands which may or may not be
builtins (such as "echo" which, historically, was not always a
builtin), and non-builtins commands, such as "sed" and "tr".
So, for the commit message, perhaps simply:
Extend the shell-scripting section of CodingGuidelines to suggest
octal escape sequences (e.g. "\302\242") over hexadecimal
(e.g. "\xc2\xa2") since the latter can be a source of portability
problems.
As for the change to CodingGuidelines, this would probably be sufficient:
Use octal escape sequences (e.g. "\302\242"), not hexadecimal
(e.g. "\xc2\xa2"), since the latter is not portable across some
commands, such as `printf`, `sed`, `tr`, etc.
