1	#!/usr/bin/env bash
2	#
3	# NOTE:
4	# - $! is tested in background.test.sh
5	# - $- is tested in sh-options
6	#
7	# TODO: It would be nice to make a table, like:
8	#
9	# $$ $BASHPID $PPID $SHLVL $BASH_SUBSHELL
10	# X
11	# (Subshell, Command Sub, Pipeline, Spawn $0)
12	#
13	# And see whether the variable changed.
14
15	#### $PWD
16	# Just test that it has a slash for now.
17	echo $PWD | grep -o /
18	## status: 0
19
20	#### $1 .. $9 are scoped, while $0 is not
21	func() { echo $0 $1 $2 | sed -e 's/.*sh/sh/'; }
22	func a b
23	## stdout: sh a b
24
25	#### $?
26	echo $? # starts out as 0
27	sh -c 'exit 33'
28	echo $?
29	## stdout-json: "0\n33\n"
30	## status: 0
31
32	#### $#
33	set -- 1 2 3 4
34	echo $#
35	## stdout: 4
36	## status: 0
37
38	#### $_
39	# This is bash-specific.
40	echo hi
41	echo $_
42	## stdout-json: "hi\nhi\n"
43	## N-I dash/mksh stdout-json: "hi\n\n"
44
45	#### $$ looks like a PID
46	# Just test that it has decimal digits
47	echo $$ | egrep '[0-9]+'
48	## status: 0
49
50	#### $$ doesn't change with subshell or command sub
51	# Just test that it has decimal digits
52	set -o errexit
53	die() {
54	echo 1>&2 "$@"; exit 1
55	}
56	parent=$$
57	test -n "$parent" || die "empty PID in parent"
58	( child=$$
59	test -n "$child" || die "empty PID in subshell"
60	test "$parent" = "$child" || die "should be equal: $parent != $child"
61	echo 'subshell OK'
62	)
63	echo $( child=$$
64	test -n "$child" || die "empty PID in command sub"
65	test "$parent" = "$child" || die "should be equal: $parent != $child"
66	echo 'command sub OK'
67	)
68	exit 3 # make sure we got here
69	## status: 3
70	## STDOUT:
71	subshell OK
72	command sub OK
73	## END
74
75	#### $BASHPID DOES change with subshell and command sub
76	set -o errexit
77	die() {
78	echo 1>&2 "$@"; exit 1
79	}
80	parent=$BASHPID
81	test -n "$parent" || die "empty BASHPID in parent"
82	( child=$BASHPID
83	test -n "$child" || die "empty BASHPID in subshell"
84	test "$parent" != "$child" || die "should not be equal: $parent = $child"
85	echo 'subshell OK'
86	)
87	echo $( child=$BASHPID
88	test -n "$child" || die "empty BASHPID in command sub"
89	test "$parent" != "$child" ||
90	die "should not be equal: $parent = $child"
91	echo 'command sub OK'
92	)
93	exit 3 # make sure we got here
94	## status: 3
95	## STDOUT:
96	subshell OK
97	command sub OK
98	## END
99	## N-I dash status: 1
100	## N-I dash stdout-json: ""
101
102	#### Background PID $! looks like a PID
103	sleep 0.01 &
104	pid=$!
105	wait
106	echo $pid | egrep '[0-9]+' >/dev/null
107	echo status=$?
108	## stdout: status=0
109
110	#### $PPID
111	echo $PPID | egrep '[0-9]+'
112	## status: 0
113
114	# NOTE: There is also $BASHPID
115
116	#### $PIPESTATUS
117	echo hi | sh -c 'cat; exit 33' | wc -l >/dev/null
118	argv.py "${PIPESTATUS[@]}"
119	## status: 0
120	## stdout: ['0', '33', '0']
121	## N-I dash stdout-json: ""
122	## N-I dash status: 2
123
124	#### $RANDOM
125	expr $0 : '.*/osh$' && exit 99 # Disabled because of spec-runner.sh issue
126	echo $RANDOM | egrep '[0-9]+'
127	## status: 0
128	## N-I dash status: 1
129
130	#### $UID and $EUID
131	# These are both bash-specific.
132	set -o errexit
133	echo $UID | egrep -o '[0-9]+' >/dev/null
134	echo $EUID | egrep -o '[0-9]+' >/dev/null
135	echo status=$?
136	## stdout: status=0
137	## N-I dash/mksh stdout-json: ""
138	## N-I dash/mksh status: 1