Beginner in regular expression
def showRE(a,re)
if a =~ re
"#{$`}<<#{$&}>>#{$'}"
else
"no match"
end
end
showRE('He said "Hello"', /(["']).*?1/)
#=> "He said <<"Hello">>"
Can someone please explain why this function returns "Hello". More specifically, the purpose of *? and how that results in function returning what it does. I know ["'] finds either '/"' or '/'' and 1 refers to the match of the first group. However shouldn't that return -> 'He said Hello"' since '/'' is the first line of the string that represents what is in the brackets?
ruby-on-rails ruby regex
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
add a comment |
def showRE(a,re)
if a =~ re
"#{$`}<<#{$&}>>#{$'}"
else
"no match"
end
end
showRE('He said "Hello"', /(["']).*?1/)
#=> "He said <<"Hello">>"
Can someone please explain why this function returns "Hello". More specifically, the purpose of *? and how that results in function returning what it does. I know ["'] finds either '/"' or '/'' and 1 refers to the match of the first group. However shouldn't that return -> 'He said Hello"' since '/'' is the first line of the string that represents what is in the brackets?
ruby-on-rails ruby regex
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
1
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45
add a comment |
def showRE(a,re)
if a =~ re
"#{$`}<<#{$&}>>#{$'}"
else
"no match"
end
end
showRE('He said "Hello"', /(["']).*?1/)
#=> "He said <<"Hello">>"
Can someone please explain why this function returns "Hello". More specifically, the purpose of *? and how that results in function returning what it does. I know ["'] finds either '/"' or '/'' and 1 refers to the match of the first group. However shouldn't that return -> 'He said Hello"' since '/'' is the first line of the string that represents what is in the brackets?
ruby-on-rails ruby regex
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
def showRE(a,re)
if a =~ re
"#{$`}<<#{$&}>>#{$'}"
else
"no match"
end
end
showRE('He said "Hello"', /(["']).*?1/)
#=> "He said <<"Hello">>"
Can someone please explain why this function returns "Hello". More specifically, the purpose of *? and how that results in function returning what it does. I know ["'] finds either '/"' or '/'' and 1 refers to the match of the first group. However shouldn't that return -> 'He said Hello"' since '/'' is the first line of the string that represents what is in the brackets?
ruby-on-rails ruby regex
ruby-on-rails ruby regex
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
edited Nov 15 '18 at 5:14
Cary Swoveland
69.6k54166
69.6k54166
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
asked Nov 14 '18 at 19:19
LawleyendaLawleyenda
359
359
This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
1
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45
add a comment |
This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
1
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45
This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
1
1
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45
add a comment |
1 Answer
1
active
oldest
votes
The regular expression being passed as an argument (which I'll write in "free-spacing" mode, to make it self-documenting), is as follows:
r = /
( # start capture group 1
["'] # match a double or single parenthesis (a "character class")
) # end capture group 1
.* # match zero or more (`*`) characters (any characters)
? # make the foregoing match (.*) lazy
1 # match the contents of capture group 1
/x # free-spacing regex definition mode
str = 'He said "Hello"'
#=> "He said "Hello""
str =~ r
#=> 8 (we have a match beginning at str[8])
As str =~ r is "truthy", we evaluate
"#{$`}<<#{$&}>>#{$'}"
=> "He said <<"Hello">>"
The key here is that there are three global variables in this expression:
$` #=> "He said "
$& #=> ""Hello""
$' #=> ""
The meanings of these variables are given in this doc. You will see that:
- $` contains the string to the left of the last successful match;
- $& contains the string matched by the last successful match; and
- $' contains the string to the right of the last successful match.
So we have (and return)
"#{"He said "}<<#{""Hello""}>>#{""}"
#=> => "He said <<"Hello">>"
We could alternatively use the class method Regexp::last_match:
last_match = Regexp.last_match
#=> #<MatchData ""Hello"" 1:""">
last_match is an instance of the class MatchData. That class contains many useful methods, including ones that return the values of the three global variables mentioned above:
last_match.pre_match #=> "He said "
last_match[0] #=> ""Hello""
last_match.post_match #=> ""
I cannot say why the match .* in the regular expression was made lazy (by making it .*?).
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The regular expression being passed as an argument (which I'll write in "free-spacing" mode, to make it self-documenting), is as follows:
r = /
( # start capture group 1
["'] # match a double or single parenthesis (a "character class")
) # end capture group 1
.* # match zero or more (`*`) characters (any characters)
? # make the foregoing match (.*) lazy
1 # match the contents of capture group 1
/x # free-spacing regex definition mode
str = 'He said "Hello"'
#=> "He said "Hello""
str =~ r
#=> 8 (we have a match beginning at str[8])
As str =~ r is "truthy", we evaluate
"#{$`}<<#{$&}>>#{$'}"
=> "He said <<"Hello">>"
The key here is that there are three global variables in this expression:
$` #=> "He said "
$& #=> ""Hello""
$' #=> ""
The meanings of these variables are given in this doc. You will see that:
- $` contains the string to the left of the last successful match;
- $& contains the string matched by the last successful match; and
- $' contains the string to the right of the last successful match.
So we have (and return)
"#{"He said "}<<#{""Hello""}>>#{""}"
#=> => "He said <<"Hello">>"
We could alternatively use the class method Regexp::last_match:
last_match = Regexp.last_match
#=> #<MatchData ""Hello"" 1:""">
last_match is an instance of the class MatchData. That class contains many useful methods, including ones that return the values of the three global variables mentioned above:
last_match.pre_match #=> "He said "
last_match[0] #=> ""Hello""
last_match.post_match #=> ""
I cannot say why the match .* in the regular expression was made lazy (by making it .*?).
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
add a comment |
The regular expression being passed as an argument (which I'll write in "free-spacing" mode, to make it self-documenting), is as follows:
r = /
( # start capture group 1
["'] # match a double or single parenthesis (a "character class")
) # end capture group 1
.* # match zero or more (`*`) characters (any characters)
? # make the foregoing match (.*) lazy
1 # match the contents of capture group 1
/x # free-spacing regex definition mode
str = 'He said "Hello"'
#=> "He said "Hello""
str =~ r
#=> 8 (we have a match beginning at str[8])
As str =~ r is "truthy", we evaluate
"#{$`}<<#{$&}>>#{$'}"
=> "He said <<"Hello">>"
The key here is that there are three global variables in this expression:
$` #=> "He said "
$& #=> ""Hello""
$' #=> ""
The meanings of these variables are given in this doc. You will see that:
- $` contains the string to the left of the last successful match;
- $& contains the string matched by the last successful match; and
- $' contains the string to the right of the last successful match.
So we have (and return)
"#{"He said "}<<#{""Hello""}>>#{""}"
#=> => "He said <<"Hello">>"
We could alternatively use the class method Regexp::last_match:
last_match = Regexp.last_match
#=> #<MatchData ""Hello"" 1:""">
last_match is an instance of the class MatchData. That class contains many useful methods, including ones that return the values of the three global variables mentioned above:
last_match.pre_match #=> "He said "
last_match[0] #=> ""Hello""
last_match.post_match #=> ""
I cannot say why the match .* in the regular expression was made lazy (by making it .*?).
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
add a comment |
The regular expression being passed as an argument (which I'll write in "free-spacing" mode, to make it self-documenting), is as follows:
r = /
( # start capture group 1
["'] # match a double or single parenthesis (a "character class")
) # end capture group 1
.* # match zero or more (`*`) characters (any characters)
? # make the foregoing match (.*) lazy
1 # match the contents of capture group 1
/x # free-spacing regex definition mode
str = 'He said "Hello"'
#=> "He said "Hello""
str =~ r
#=> 8 (we have a match beginning at str[8])
As str =~ r is "truthy", we evaluate
"#{$`}<<#{$&}>>#{$'}"
=> "He said <<"Hello">>"
The key here is that there are three global variables in this expression:
$` #=> "He said "
$& #=> ""Hello""
$' #=> ""
The meanings of these variables are given in this doc. You will see that:
- $` contains the string to the left of the last successful match;
- $& contains the string matched by the last successful match; and
- $' contains the string to the right of the last successful match.
So we have (and return)
"#{"He said "}<<#{""Hello""}>>#{""}"
#=> => "He said <<"Hello">>"
We could alternatively use the class method Regexp::last_match:
last_match = Regexp.last_match
#=> #<MatchData ""Hello"" 1:""">
last_match is an instance of the class MatchData. That class contains many useful methods, including ones that return the values of the three global variables mentioned above:
last_match.pre_match #=> "He said "
last_match[0] #=> ""Hello""
last_match.post_match #=> ""
I cannot say why the match .* in the regular expression was made lazy (by making it .*?).
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
The regular expression being passed as an argument (which I'll write in "free-spacing" mode, to make it self-documenting), is as follows:
r = /
( # start capture group 1
["'] # match a double or single parenthesis (a "character class")
) # end capture group 1
.* # match zero or more (`*`) characters (any characters)
? # make the foregoing match (.*) lazy
1 # match the contents of capture group 1
/x # free-spacing regex definition mode
str = 'He said "Hello"'
#=> "He said "Hello""
str =~ r
#=> 8 (we have a match beginning at str[8])
As str =~ r is "truthy", we evaluate
"#{$`}<<#{$&}>>#{$'}"
=> "He said <<"Hello">>"
The key here is that there are three global variables in this expression:
$` #=> "He said "
$& #=> ""Hello""
$' #=> ""
The meanings of these variables are given in this doc. You will see that:
- $` contains the string to the left of the last successful match;
- $& contains the string matched by the last successful match; and
- $' contains the string to the right of the last successful match.
So we have (and return)
"#{"He said "}<<#{""Hello""}>>#{""}"
#=> => "He said <<"Hello">>"
We could alternatively use the class method Regexp::last_match:
last_match = Regexp.last_match
#=> #<MatchData ""Hello"" 1:""">
last_match is an instance of the class MatchData. That class contains many useful methods, including ones that return the values of the three global variables mentioned above:
last_match.pre_match #=> "He said "
last_match[0] #=> ""Hello""
last_match.post_match #=> ""
I cannot say why the match .* in the regular expression was made lazy (by making it .*?).
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
edited Nov 15 '18 at 8:15
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
answered Nov 15 '18 at 5:40
Cary SwovelandCary Swoveland
69.6k54166
69.6k54166
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
add a comment |
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Really Impressive
– Mayur Shah
Nov 15 '18 at 5:45
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
Thanks a bunch!
– Lawleyenda
Nov 15 '18 at 14:02
add a comment |
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This indentation is really anarchy. Can you clean that up? It helps us understand what you're trying to do.
– tadman
Nov 14 '18 at 20:43
1
A good regular expression explainer can help illuminate what that regular expression is doing. Barring that, a good primer book is a good way to go.
– tadman
Nov 14 '18 at 20:45