Re: [PATCH] test: Fix printf error when debug is enabled

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Sep 30, 2025 at 12:24:17AM +0200, Stefano Brivio wrote:
> On Mon, 29 Sep 2025 14:30:14 +0800
> Yumei Huang <yuhuang@redhat.com> wrote:
> 
> > Running test pasta/tcp with debug enabled would get stuck with
> > below error:
> > 
> >   + printf 'DEBUG: ns     socat -u OPEN:__BASEPATH__/big.bin TCP6:[__GW6__%__IFNAME__]:10003\n'
> >   lib/term: line 38: printf: `_': invalid format character
> > 
> > The error occurs because printf interprets the % character as the
> > start of a format specifier, and the following '_' isn't one of
> > them.
> > 
> > Fix it by replacing 'printf "${*}\n"' with 'printf "%s\n" "$*"'.
> 
> I'm not sure why, but this breaks colour highlights for me. Instead of
> seeing a part of this message in blue, now I get:
> 
>   Test layout: \033[1;34msingle passt instance with guest\033[0m.\n
> 
> I can look into it if it only happens for me, or if needed.

Oh, that's interesting.  I believe the colouring has been broken
forever on Fedora, but I never got around to looking into it.
Figuring this out might reveal why.  Maybe.

I realised I think I know why: those colour codes rely on turning
"\033" into a terminal escape.  printf(1) will do that in the format
string, but not in %s parameters

	$ printf "a\tb%sc\n " "\t"
	a	b\tc

We can fix this either by moving the escape codes back into the format
string, or using %b instead of %s, which explicitly interprets string
escape codes.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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