1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
# $NetBSD: var-op-shell.mk,v 1.6 2022/01/10 20:32:29 rillig Exp $
#
# Tests for the != variable assignment operator, which runs its right-hand
# side through the shell.
# The variable OUTPUT gets the output from running the shell command.
OUTPUT!= echo "success"'ful'
.if ${OUTPUT} != "successful"
. error
.endif
# Since 2014-08-20, the output of the shell command may be empty.
#
# On 1996-05-29, when the '!=' assignment operator and Cmd_Exec were added,
# an empty output produced the error message "Couldn't read shell's output
# for \"%s\"".
#
# The error message is still in Cmd_Exec but reserved for technical errors.
# It may be possible to trigger the error message by killing the shell after
# reading part of its output.
OUTPUT!= true
.if ${OUTPUT} != ""
. error
.endif
# The output of a shell command that failed is processed nevertheless.
# Unlike the other places that run external commands (expression modifier
# '::!=', expression modifier ':!...!'), a failed command generates only a
# warning, not an "error". These "errors" are ignored in default mode, for
# compatibility, but not in lint mode (-dL).
OUTPUT!= echo "failed"; false
.if ${OUTPUT} != "failed"
. error
.endif
# A command with empty output may fail as well.
OUTPUT!= false
.if ${OUTPUT} != ""
. error
.endif
# In the output of the command, each newline is replaced with a space.
# Except for the very last one, which is discarded.
OUTPUT!= echo "line 1"; echo "line 2"
.if ${OUTPUT} != "line 1 line 2"
. error
.endif
# A failing command in the middle results in the exit status 0, which in the
# end means that the whole sequence of commands succeeded.
OUTPUT!= echo "before"; false; echo "after"
.if ${OUTPUT} != "before after"
. error
.endif
# This should result in a warning about "exited on a signal".
# This used to be kill -14 (SIGALRM), but that stopped working on
# Darwin18 after recent update.
OUTPUT!= kill $$$$
.if ${OUTPUT} != ""
. error
.endif
# A nonexistent command produces a non-zero exit status.
OUTPUT!= /bin/no/such/command
.if ${OUTPUT} != ""
. error
.endif
# The output from the shell's stderr is not captured, it just passes through.
OUTPUT!= echo "stdout"; echo "stderr" 1>&2
.if ${OUTPUT} != "stdout"
. error
.endif
# The 8 dollar signs end up as 4 dollar signs when expanded. The shell sees
# the command "echo '$$$$'". The 4 dollar signs are stored in OUTPUT, and
# when that variable is expanded, they expand to 2 dollar signs.
OUTPUT!= echo '$$$$$$$$'
.if ${OUTPUT} != "\$\$"
. error
.endif
# As a debugging aid, log the exact command that is run via the shell.
.MAKEFLAGS: -dv
OUTPUT!= echo '$$$$$$$$'
.MAKEFLAGS: -d0
all:
|
