37 lines
1.4 KiB
Makefile
37 lines
1.4 KiB
Makefile
# $NetBSD: varmod-assign-shell.mk,v 1.4 2022/01/10 20:32:29 rillig Exp $
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#
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# Tests for the variable modifier '::!=', which assigns the output of a shell
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# command to the variable, but only if the command exited successfully. This
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# is different from the other places that capture the output of an external
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# command (variable assignment operator '!=', expression modifier ':sh',
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# expression modifier ':!...!'), which also use the output when the shell
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# command fails or crashes.
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#
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# The variable modifier '::!=' and its close relatives have been around since
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# var.c 1.45 from 2000-06-01.
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#
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# Before 2020.08.25.21.16.53, the variable modifier '::!=' had a bug for
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# unsuccessful commands, it put the previous value of the variable into the
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# error message instead of the command that was executed. That's where the
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# counterintuitive error message 'make: "previous" returned non-zero status'
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# comes from.
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#
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# BUGS
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# Even though the variable modifier '::!=' produces an error message,
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# the exit status of make is still 0.
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#
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# Having an error message instead of a warning like for the variable
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# assignment operator '!=' is another unnecessary inconsistency.
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DIRECT= previous
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DIRECT!= echo output; false
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ASSIGNED= previous
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.MAKEFLAGS: -dv # to see the actual command
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_:= ${ASSIGNED::!=echo output; ${:Ufalse}}
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.MAKEFLAGS: -d0
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all:
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@echo DIRECT=${DIRECT:Q}
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@echo ASSIGNED=${ASSIGNED:Q}
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