Why doesn't this file read work for me?

Ruby
1

Hi,
I need to open files, just the first 75 bytes of them, and determine if
there’s a string in the data. If the string is there, then, I do
something. If not, then I do something else.

Here’s my IRB try. I don’t understand why it’s coming back to me with a
positive, meaning, it seems to see the string, when, the string
definitely isn’t in the file.

Thanks,
Peter

L:\eps\fedreg>irb
irb(main):001:0> stuff = File.open(“f3153013.eps”) { |f| f.read(75) }
=> “%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: 0 0 552
704\n%%HiResBoundingBox: 0.00”
irb(main):002:0> if stuff.to_s.scan(/^%%Creator: MathType/) then
irb(main):003:1* puts “MathType file.”
irb(main):004:1> else
irb(main):005:1* puts “NOT MathType file.”
irb(main):006:1> end
mathtype file.
=> nil
irb(main):007:0>

2

On Jan 3, 2008 2:28 PM, Peter B. [email protected] wrote:

Peter

L:\eps\fedreg>irb
irb(main):001:0> stuff = File.open(“f3153013.eps”) { |f| f.read(75) }
=> “%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: 0 0 552
704\n%%HiResBoundingBox: 0.00”
irb(main):002:0> if stuff.to_s.scan(/^%%Creator: MathType/) then

String#scan returns an array. So you can check the size.

if stuff.to_s.scan(/^%%Creator: MathType/).size == 0

Or you can simple use String#match instead which is the behavior you are
looking for.

if stuff.to_s.match(/^%%Creator: MathType/)

HTH,
Michael G.

3

Alle giovedì 3 gennaio 2008, Peter B. ha scritto:

Peter
irb(main):006:1> end
mathtype file.
=> nil
irb(main):007:0>

Because String#scan always returns an array, which is empty if there
were no
match, but which is always true. You should replace

if stuff.to_s.scan(…) then

with

unless stuff.to_s.scan(…).empty? then

If you only want to check whether stuff contains that substring, I think
you
should use String#match, not String#scan. String#match returns an object
of
class MatchData if there’s a match and nil otherwise, which allows you
to use
the conditional like you did your code (check the ri documentation for
String#scan and String#match for more details).

By the way, why do you call to_s on the result of File.open ? Isn’t it
already
a string?

I hope this helps

Stefano

4

String#scan returns an array. So you can check the size.

if stuff.to_s.scan(/^%%Creator: MathType/).size == 0

Or you can simple use String#match instead which is the behavior you are
looking for.

if stuff.to_s.match(/^%%Creator: MathType/)

HTH,
Michael G.

Thank you very much, Michael. I used .match and it works fine now.

5

If you only want to check whether stuff contains that substring, I think
you
should use String#match, not String#scan. String#match returns an object
of
class MatchData if there’s a match and nil otherwise, which allows you
to use
the conditional like you did your code (check the ri documentation for
String#scan and String#match for more details).

By the way, why do you call to_s on the result of File.open ? Isn’t it
already
a string?

I hope this helps

Stefano

Yup. This helps a lot. I used .match and it worked beautifully.
Regarding the .to_s thing, that’s just me being neurotic and thinking I
needed it. No, I don’t need it.