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Date: Tue, 4 Jun 2019 09:01:31 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Masahiro Yamada' <yamada.masahiro@...ionext.com> CC: "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>, "Vineet Gupta" <vgupta@...opsys.com>, Alexey Brodkin <abrodkin@...opsys.com>, "linux-snps-arc@...ts.infradead.org" <linux-snps-arc@...ts.infradead.org>, linux-stable <stable@...r.kernel.org>, Michal Marek <michal.lkml@...kovi.net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix From: Masahiro Yamada > Sent: 04 June 2019 04:31 ... > > > > You could use: > > > > $(shell sh -c "command -v $(c)gcc") > > > > or maybe: > > > > $(shell command$${x:+} -v $(c)gcc) > > > > > > > > > How about this? > > > > > > $(shell : ~; command -v $(c)gcc) > > > > Overcomplicated .... > > > > I've not looked at the list of 'special characters' in make, > > but I suspect any variable expansion is enough. > > Since ${x:+} always expands to the empty string (whether or > > not 'x' is defined) it can't have any unfortunate side effects. > > > Probably, my eyes are used to Makefile. > ":" is a no-op command, and it is used everywhere in kernel Makefiles > in the form of "@:' > > It depends on people which solution seems simpler. > So, this argument tends to end up with bikesheding. I am fully aware of ':', it is a shell builtin that always return success. Usually used when you want the side-effects of substitutions without executing anything (eg : ${foo:=bar} ), to change the result of a sequence of shell commands or as a dummy (eg while :; do :; done; ) Very annoyingly bash parses !: as something other than 'not true'. $(shell command$${x:+} -v $(c)gcc) will be marginally faster because it is less parsing. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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