Hi
I am using regexp in a loop to extract a value from a
string. I have noticed that when string is nil $1 keeps its
old value, which means that the expression after regexp
does not get the correct value (which should be nil). The
code looks like this
(0..key_colnames.length-1).each do |i|
person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
# assigning $1 to something
end
Shouldn't the $-variables be reset after each regexp? Or is
it a better way to do this?
/Anders Vesterberg
http://www.vesterberg.se
Hi
I am using regexp in a loop to extract a value from a
string. I have noticed that when string is nil $1 keeps its
old value, which means that the expression after regexp
does not get the correct value (which should be nil). The
code looks like this
(0..key_colnames.length-1).each do |i|
person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
# assigning $1 to something
end
Shouldn't the $-variables be reset after each regexp? Or is
it a better way to do this?
/Anders Vesterberg
http://www.vesterberg.se
The problem is in your regex. It will match a word containing hyphens or :
but it will also match an empty string!
a = /\"?([\w\-:]*)\"?/
=>
/\"?([\w\-:]*)\"?/
"This is a String" =~ a
=>
0
$1
=>
"This"
"" =~ a
=>
0
$1
=>
""
"$12dc" =~ a
=>
0
$1
=> ""
Without knowing very much about the requirements of your regex, you need to
replace the * wildcard ( zero or more ) with + (one or more)
a = /\"?([\w\-:]+)\"?/
=>
/\"?([\w\-:]+)\"?/
"This is a String" =~ a
=>
0
$1
=>
"This"
"" =~ a
=>
nil
$1
=>
nil
"$12dc" =~ a
=>
1
$1
=> "12dc"
Nils as you would expect. You could also make the first line it a touch
more rubyish 
key_colnames.each do |key|
person_data[key] =~ /\"?([\w\-:])\"/
# do your thing with $1
end
···
On 8/8/06, Anders Vesterberg <anders1@vesdakon.se> wrote:
Anders Vesterberg wrote:
Hi
I am using regexp in a loop to extract a value from a
string. I have noticed that when string is nil $1 keeps its
old value, which means that the expression after regexp
does not get the correct value (which should be nil). The
code looks like this
(0..key_colnames.length-1).each do |i|
person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
# assigning $1 to something
end
Shouldn't the $-variables be reset after each regexp? Or is
it a better way to do this?
I know this doesn't answer your question as to why it works that way,
but you could instead write:
(0..key_colnames.length-1).each do |i|
if person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
# assigning $1 to something
end
end
or even:
(0..key_colnames.length-1).each do |i|
myvar = (person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/) ?
$1 :
nil
end
Incidentally, what version of Ruby are you using? I was unable to
reproduce this behavior on Ruby 1.8.4 on Windows. This sample program:
"boom" =~ /(o)/
puts "$1 = #{$1.inspect}"
"boom" =~ /(a)/
puts "$1 = #{$1.inspect}"
"boom" =~ /(o)/
puts "$1 = #{$1.inspect}"
yields this output:
$1 = "o"
$1 = nil
$1 = "o"