threads / patch / 59858

v2CodingGuidelines: use octal escapes, not hex

Subject: [PATCH v2] CodingGuidelines: use octal escapes, not hex

## tl;dr

4 messages between Jun 14, 2023 and Jun 14, 2023. Diffs are folded; open one to read it.

replies: 3people: 2as markdown or json

Jonathan Tan· Jun 14, 2023, 00:15 UTC · lore

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.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
I've used Eric's suggestion for the commit message and limited the scope
of the documentation change to printf.
Version 1 was here:
https://lore.kernel.org/git/20230613172927.19019-1-jonathantanmy@google.com/
---
 Documentation/CodingGuidelines | 4 ++++
 1 file changed, 4 insertions(+)
Show changes to Documentation/CodingGuidelines +4 −0
diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 003393ed16..30ac7d2d3f 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -188,6 +188,10 @@ For shell scripts specifically (not exhaustive):
    hopefully nobody starts using "local" before they are reimplemented
    in C ;-)
 
+ - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
+   "\xc2\xa2"), since the latter is not portable across commands like
+   "printf".
+
 
 For C programs:
 

-- 
2.41.0.162.gfafddb0af9-goog
Junio C Hamano· Jun 14, 2023, 00:28 UTC · re: Jonathan Tan · lore

Re: [PATCH v2] CodingGuidelines: use octal escapes, not hex

Jonathan Tan <jonathantanmy@google.com> writes:
Show 26 quoted lines
> 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.
>
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
> I've used Eric's suggestion for the commit message and limited the scope
> of the documentation change to printf.
>
> Version 1 was here:
> https://lore.kernel.org/git/20230613172927.19019-1-jonathantanmy@google.com/
> ---
>  Documentation/CodingGuidelines | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
> index 003393ed16..30ac7d2d3f 100644
> --- a/Documentation/CodingGuidelines
> +++ b/Documentation/CodingGuidelines
> @@ -188,6 +188,10 @@ For shell scripts specifically (not exhaustive):
>     hopefully nobody starts using "local" before they are reimplemented
>     in C ;-)
>  
> + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
> +   "\xc2\xa2"), since the latter is not portable across commands like
> +   "printf".
I'd say
    - Use octal ... not hex..., in printf format string.
not "commands LIKE".
Thanks.
Jonathan Tan· Jun 14, 2023, 21:31 UTC · re: Jonathan Tan · lore

[PATCH v3] CodingGuidelines: use octal escapes, not hex

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.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
Changes in v3: Used Junio's suggestion [1].
[1] https://lore.kernel.org/git/xmqqy1km28g9.fsf@gitster.g/
---
Range-diff against v2:
1:  c775a0db22 ! 1:  0b7d3ed8f5 CodingGuidelines: use octal escapes, not hex
    @@ Commit message
     
         Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
         ---
    -    I've used Eric's suggestion for the commit message and limited the scope
    -    of the documentation change to printf.
    +    Changes in v3: Used Junio's suggestion [1].
     
    -    Version 1 was here:
    -    https://lore.kernel.org/git/20230613172927.19019-1-jonathantanmy@google.com/
    +    [1] https://lore.kernel.org/git/xmqqy1km28g9.fsf@gitster.g/
     
      ## Documentation/CodingGuidelines ##
     @@ Documentation/CodingGuidelines: For shell scripts specifically (not exhaustive):
    @@ Documentation/CodingGuidelines: For shell scripts specifically (not exhaustive):
         in C ;-)
      
     + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
    -+   "\xc2\xa2"), since the latter is not portable across commands like
    -+   "printf".
    ++   "\xc2\xa2") in printf format strings, since hexadecimal escape
    ++   sequences are not portable.
     +
      
      For C programs:
 Documentation/CodingGuidelines | 4 ++++
 1 file changed, 4 insertions(+)
Show changes to Documentation/CodingGuidelines +4 −0
diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 003393ed16..39ef53c237 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -188,6 +188,10 @@ For shell scripts specifically (not exhaustive):
    hopefully nobody starts using "local" before they are reimplemented
    in C ;-)
 
+ - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
+   "\xc2\xa2") in printf format strings, since hexadecimal escape
+   sequences are not portable.
+
 
 For C programs:
 

-- 
2.41.0.162.gfafddb0af9-goog
Junio C Hamano· Jun 14, 2023, 21:54 UTC · re: Jonathan Tan · lore

Re: [PATCH v3] CodingGuidelines: use octal escapes, not hex

Jonathan Tan <jonathantanmy@google.com> writes:
> 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.

Sounds good. On a typical GNU system, /usr/bin/printf as well as printf built into bash groks "\x<hex>" escapes in its format string, but we cannot depend on it because POSIX does not require support for "\x<hex>", and printf built into dash indeed does not. It is a good idea to stress that this is specifically about the format string (in other words, nothing magical happens when using octal or hex escapes in say "printf '%s\n' '\302\242'").

> + - Use octal escape sequences (e.g. "\302\242"), not hexadecimal (e.g.
> +   "\xc2\xa2") in printf format strings, since hexadecimal escape
> +   sequences are not portable.
Will queue.  Thanks.

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