1 files changed, 78 insertions, 3 deletions
diff --git a/unit-tests/var-op-shell.mk b/unit-tests/var-op-shell.mk
index 83580a89e6c2..7b52513e1131 100644
--- a/unit-tests/var-op-shell.mk
+++ b/unit-tests/var-op-shell.mk
@@ -1,9 +1,84 @@
-# $NetBSD: var-op-shell.mk,v 1.2 2020/08/16 14:25:16 rillig Exp $
+# $NetBSD: var-op-shell.mk,v 1.3 2020/11/09 20:39:46 rillig Exp $
 #
 # Tests for the != variable assignment operator, which runs its right-hand
 # side through the shell.
 
-# TODO: Implementation
+# 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 there 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.
+# TODO: Make this an error in lint mode.
+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
+
+# NB: The signal number must be numeric since some shells (which ones?) don't
+# accept symbolic signal names.  14 is typically SIGALRM.
+#
+# XXX: The number of the signal is not mentioned in the warning since that
+# would have been difficult to implement; currently the errfmt is a format
+# string containing a single %s conversion.
+OUTPUT!=	kill -14 $$$$
+.if ${OUTPUT} != ""
+.  error
+.endif
+
+# A nonexistent command produces a non-zero exit status.
+OUTPUT!=	/bin/no/such/command
+.if ${OUTPUT} != ""
+.  error
+.endif
+
+# The output from the shell's stderr is not captured, it just passes through.
+OUTPUT!=	echo "stdout"; echo "stderr" 1>&2
+.if ${OUTPUT} != "stdout"
+.  error
+.endif
+
+# The 8 dollar signs end up as 4 dollar signs when expanded.  The shell sees
+# the command "echo '$$$$'".  The 4 dollar signs are stored in OUTPUT, and
+# when that variable is expanded, they expand to 2 dollar signs.
+OUTPUT!=	echo '$$$$$$$$'
+.if ${OUTPUT} != "\$\$"
+.  error
+.endif
 
 all:
-	@:;