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[v3] CodingGuidelines: use octal escapes, not hex

Message ID 20230614213145.475607-1-jonathantanmy@google.com (mailing list archive)
State Accepted
Commit f0b68f0546a44e2bc3a764bd75b3aa4418c01601
Headers show
Series [v3] CodingGuidelines: use octal escapes, not hex | expand

Commit Message

Jonathan Tan June 14, 2023, 9:31 p.m. UTC 
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(+)

Comments

Junio C Hamano June 14, 2023, 9:54 p.m. UTC | #1 
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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Patch

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: