I'm trying to parse (in Ruby) what's effectively the UNIX passwd file-format: comma delimiters, with an escape character \\
such that anything escaped should be considered literally. I'm trying to use a regular expression for this, but I'm coming up short — even when using Oniguruma for lookahead/lookbehind assertions.
Essentially, all of the following should work:
a,b,c # => ["a", "b", "c"]
\a,b\,c # => ["a", "b,c"]
a,b,c\
d # => ["a", "b", "c\nd"]
a,b\\\,c # => ["a", "b\,c"]
Any ideas?
The first response looks pretty good. With a file containing
\a,,b\\\,c\,d,e\\f,\\,\
g
it gives:
[["\\a,"], [","], ["b\\\\\\,c\\,d,"], ["e\\\\f,"], ["\\\\,"], ["\\\ng\n"], [""]]
which is pretty close. I don't need the unescaping done on this first pass, as long as everything splits correctly on the commas. I tried Oniguruma and ended up with (the much longer):
Oniguruma::ORegexp.new(%{
(?: # - begins with (but doesn't capture)
(?<=\A) # - start of line
| # - (or)
(?<=,) # - a comma
)
(?: # - contains (but doesn't capture)
.*? # - any set of characters
[^\\\\]? # - not ending in a slash
(\\\\\\\\)* # - followed by an even number of slashes
)*?
(?: # - ends with (but doesn't capture)
(?=\Z) # - end of line
| # - (or)
(?=,)) # - a comma
},
'mx'
).scan(s)
Try this:
s.scan(/((?:\\.|[^,])*,?)/m)
It doesn't translate the characters following a \\, but that can be done afterwards as a separate step.
I'd give the CSV class a try.
And a regex solution (hack?) might look like this:
#!/usr/bin/ruby -w
# contents of test.csv:
# a,b,c
# \a,b\,c
# a,b,c\
# d
# a,b\\\,c
file = File.new("test.csv", "r")
tokens = file.read.scan(/(?:\\.|[^,\r\n])*|\r?\n/m)
puts "-----------"
tokens.length.times do |i|
if tokens[i] == "\n" or tokens[i] == "\r\n"
puts "-----------"
else
puts ">" + tokens[i] + "<"
end
end
file.close
which will produce the output:
-----------
>a<
>b<
>c<
-----------
>\a<
>b\,c<
-----------
>a<
>b<
>c\
d<
-----------
>a<
>b\\\,c<
-----------
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