1	#!/usr/bin/env bash
2	#
3	# Only bash and zsh seem to implement [[ foo =~ '' ]]
4	#
5	# ^(a b)$ is a regex that should match 'a b' in a group.
6	#
7	# Not sure what bash is doing here... I think I have to just be empirical.
8	# Might need "compat" switch for parsing the regex. It should be an opaque
9	# string like zsh, not sure why it isn't.
10	#
11	# I think this is just papering over bugs...
12	# https://www.gnu.org/software/bash/manual/bash.html#Conditional-Constructs
13	#
14	# Storing the regular expression in a shell variable is often a useful way to
15	# avoid problems with quoting characters that are special to the shell. It is
16	# sometimes difficult to specify a regular expression literally without using
17	# quotes, or to keep track of the quoting used by regular expressions while
18	# paying attention to the shell’s quote removal. Using a shell variable to
19	# store the pattern decreases these problems. For example, the following is
20	# equivalent to the above:
21	#
22	# pattern='[[:space:]]*(a)?b'
23	# [[ $line =~ $pattern ]]
24	#
25	# If you want to match a character that’s special to the regular expression
26	# grammar, it has to be quoted to remove its special meaning. This means that in
27	# the pattern ‘xxx.txt’, the ‘.’ matches any character in the string (its usual
28	# regular expression meaning), but in the pattern ‘"xxx.txt"’ it can only match a
29	# literal ‘.’. Shell programmers should take special care with backslashes, since
30	# backslashes are used both by the shell and regular expressions to remove the
31	# special meaning from the following character. The following two sets of
32	# commands are not equivalent:
33	#
34	# From bash code: ( | ) are treated special. Normally they must be quoted, but
35	# they can be UNQUOTED in BASH_REGEX state. In fact they can't be quoted!
36
37	#### BASH_REMATCH
38	[[ foo123 =~ ([a-z]+)([0-9]+) ]]
39	argv.py "${BASH_REMATCH[@]}"
40	## STDOUT:
41	['foo123', 'foo', '123']
42	## END
43	## N-I zsh STDOUT:
44	['']
45	## END
46
47	#### Match is unanchored at both ends
48	[[ 'bar' =~ a ]] && echo true
49	## stdout: true
50
51	#### Failed match
52	[[ 'bar' =~ X ]] && echo true
53	## status: 1
54	## stdout-json: ""
55
56	#### Regex quoted with \ -- preferred in bash
57	[[ 'a b' =~ ^(a\ b)$ ]] && echo true
58	## stdout: true
59
60	#### Regex quoted with single quotes
61	# bash doesn't like the quotes
62	[[ 'a b' =~ '^(a b)$' ]] && echo true
63	## stdout-json: ""
64	## status: 1
65	## OK zsh stdout: true
66	## OK zsh status: 0
67
68	#### Regex quoted with double quotes
69	# bash doesn't like the quotes
70	[[ 'a b' =~ "^(a b)$" ]] && echo true
71	## stdout-json: ""
72	## status: 1
73	## OK zsh stdout: true
74	## OK zsh status: 0
75
76	#### Fix single quotes by storing in variable
77	pat='^(a b)$'
78	[[ 'a b' =~ $pat ]] && echo true
79	## stdout: true
80
81	#### Fix single quotes by storing in variable
82	pat="^(a b)$"
83	[[ 'a b' =~ $pat ]] && echo true
84	## stdout: true
85
86	#### Double quoting pat variable -- again bash doesn't like it.
87	pat="^(a b)$"
88	[[ 'a b' =~ "$pat" ]] && echo true
89	## stdout-json: ""
90	## status: 1
91	## OK zsh stdout: true
92	## OK zsh status: 0
93
94	#### Regex with == and not =~ is parse error, different lexer mode required
95	# They both give a syntax error. This is lame.
96	[[ '^(a b)$' == ^(a\ b)$ ]] && echo true
97	## status: 2
98	## OK zsh status: 1
99
100	#### Omitting ( )
101	[[ '^a b$' == ^a\ b$ ]] && echo true
102	## stdout: true
103
104	#### Malformed regex
105	# Are they trying to PARSE the regex? Do they feed the buffer directly to
106	# regcomp()?
107	[[ 'a b' =~ ^)a\ b($ ]] && echo true
108	## status: 2
109	## OK zsh status: 1
110
111	#### Regex with char class containing space
112	# For some reason it doesn't work without parens?
113	[[ 'ba ba ' =~ ([a b]+) ]] && echo true
114	## stdout: true
115
116	#### Operators and space lose meaning inside ()
117	[[ '< >' =~ (< >) ]] && echo true
118	## stdout: true
119	## N-I zsh stdout-json: ""
120	## N-I zsh status: 1
121
122	#### Regex with |
123	[[ 'bar' =~ foo|bar ]] && echo true
124	## stdout: true
125	## N-I zsh stdout-json: ""
126	## N-I zsh status: 1
127
128	#### Unquoted { is parse error in bash/zsh
129	[[ { =~ { ]] && echo true
130	echo status=$?
131	## STDOUT:
132	status=2
133	## END
134	## N-I zsh STDOUT:
135	status=1
136	## END
137
138	#### Quoted {
139	[[ { =~ "{" ]] && echo true
140	echo status=$?
141	## STDOUT:
142	true
143	status=0
144	## END
145	## N-I zsh STDOUT:
146	status=1
147	## END
148
149	#### Escaped {
150	# from bash-completion
151	[[ '$PA' =~ ^(\$\{?)([A-Za-z0-9_]*)$ ]] && argv.py "${BASH_REMATCH[@]}"
152	## STDOUT:
153	['$PA', '$', 'PA']
154	## END
155	## BUG zsh stdout-json: ""
156	## BUG zsh status: 1
157
158	#### Escaped { stored in variable first
159	# from bash-completion
160	pat='^(\$\{?)([A-Za-z0-9_]*)$'
161	[[ '$PA' =~ $pat ]] && argv.py "${BASH_REMATCH[@]}"
162	## STDOUT:
163	['$PA', '$', 'PA']
164	## END
165	## BUG zsh STDOUT:
166	['']
167	## END
168
169	#### regex with ?
170	[[ 'c' =~ c? ]] && echo true
171	[[ '' =~ c? ]] && echo true
172	## STDOUT:
173	true
174	true
175	## END