Another IO.popen question

ruby-talk
1

Hi,

I'm wanting to create thumbnails of pdfs in png format and send them off
to be saved. I've come up with this so far:

    IO.popen("curl #{some_uri} | convert -resize 700x700 pdf:-[0]
png:-") {|f| do_something_with_this_file}

Which works a treat. (In case you didn't know, convert is a command line
tool for ImageMagick).

What I'd really like to do though is pass on a File object to convert:

file = File.open("mypdf.pdf")

    IO.popen("#{file} | convert -resize 700x700 pdf:-[0] png:-") {|f|
do_something_with_this_file}

This obviously doesn't work but I hope illustrates what I'm wanting to
acheive - namely to pass 'file' to convert it to a png which is read
back into ruby and uploaded to my file repository on S3.

By the way, this IS for a rails application, but it seems basically like
a pure ruby question to me.

Regards

Adam

···

--
Posted via http://www.ruby-forum.com/.

2

Adam Groves wrote:

Hi,

I'm wanting to create thumbnails of pdfs in png format and send them off to be saved. I've come up with this so far:

    IO.popen("curl #{some_uri} | convert -resize 700x700 pdf:-[0] png:-") {|f| do_something_with_this_file}

Which works a treat. (In case you didn't know, convert is a command line tool for ImageMagick).

What I'd really like to do though is pass on a File object to convert:

file = File.open("mypdf.pdf")

    IO.popen("#{file} | convert -resize 700x700 pdf:-[0] png:-") {|f| do_something_with_this_file}

would this work?

file = "mypdf.pdf"
IO.popen("cat #{file} | ...")

or simply

IO.popen("convert -resize 700x700 #{file} png:-")

···

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

3

Adam Groves wrote:

Hi,

I'm wanting to create thumbnails of pdfs in png format and send them off to be saved. I've come up with this so far:

    IO.popen("curl #{some_uri} | convert -resize 700x700 pdf:-[0] png:-") {|f| do_something_with_this_file}

Which works a treat. (In case you didn't know, convert is a command line tool for ImageMagick).

What I'd really like to do though is pass on a File object to convert:

file = File.open("mypdf.pdf")

    IO.popen("#{file} | convert -resize 700x700 pdf:-[0] png:-") {|f| do_something_with_this_file}

This obviously doesn't work but I hope illustrates what I'm wanting to acheive - namely to pass 'file' to convert it to a png which is read back into ruby and uploaded to my file repository on S3.

By the way, this IS for a rails application, but it seems basically like a pure ruby question to me.

Regards

Adam

Consider RMagick: http://rmagick.rubyforge.org

The Magick::Image.read method accepts an open Ruby file object as an argument.

http://www.simplesystems.org/RMagick/doc/image1.html#read

4

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file
object (which has been uploaded from a web page form) to 'convert' and
not just a path. I should have made this clearer in my original post.

Any ideas?

···

--
Posted via http://www.ruby-forum.com/.

5

Timothy Hunter wrote:

Adam Groves wrote:

By the way, this IS for a rails application, but it seems basically like
a pure ruby question to me.

Regards

Adam

Consider RMagick: http://rmagick.rubyforge.org

The Magick::Image.read method accepts an open Ruby file object as an
argument.

RMagick 1.15.0: class Image (class and instance methods, part 1)

hmm.. Maybe you're right Tim. I was just wanting to drop to the command
line to do this and thought there must be a way of accomplishing this
without resorting to RMagick. Not that I have anything against it.

Is there really no other way of passing on a Ruby file object
imagemagick other than through RMagick?

···

--
Posted via http://www.ruby-forum.com/\.

6

yeah - that's it alright

  png = IO.popen("convert -resize 700x700 #{file} png:-"){|pipe| pipe.read}

dump it to stdout...

-a

···

On Fri, 17 Nov 2006, Joel VanderWerf wrote:

would this work?

file = "mypdf.pdf"
IO.popen("cat #{file} | ...")

or simply

IO.popen("convert -resize 700x700 #{file} png:-")

--
my religion is very simple. my religion is kindness. -- the dalai lama

7

Adam Groves wrote:

hmm.. Maybe you're right Tim. I was just wanting to drop to the command line to do this and thought there must be a way of accomplishing this without resorting to RMagick. Not that I have anything against it.

Is there really no other way of passing on a Ruby file object imagemagick other than through RMagick?
  

Consider that the convert command only accepts string options. It knows nothing about Ruby.

8

you can pass convert files on stdin. you need somthing like

   stdin = file_object.read

   cmd = " convert - png:- " # input on stdin, output to stdout

   stdout =
     IO.popen( cmd, 'r+' ) do |pipe|
       pipe.write stdin
       pipe.close_write
       pipe.read
     end

   abort "cmd <#{ cmd }> failed" unless $? == 0

   open the_png, 'w' do |f|
     f.write stdout
   end

regards.

-a

···

On Fri, 17 Nov 2006, Adam Groves wrote:

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file
object (which has been uploaded from a web page form) to 'convert' and
not just a path. I should have made this clearer in my original post.

Any ideas?

--
my religion is very simple. my religion is kindness. -- the dalai lama

9

Adam Groves wrote:

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file object (which has been uploaded from a web page form) to 'convert' and not just a path. I should have made this clearer in my original post.

Any ideas?

Untested, but maybe something like this?

file = File.open("mypdf.pdf")
IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
   while (data=file.read(N))
     f.write data
   end
end

···

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

10

Joel VanderWerf wrote:

Adam Groves wrote:

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file object (which has been uploaded from a web page form) to 'convert' and not just a path. I should have made this clearer in my original post.

Any ideas?

Untested, but maybe something like this?

file = File.open("mypdf.pdf")
IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|

                                              ^^^^^
...this bit is the problem. So Ara's r+ pipe would be necessary, unless you can put a filename here instead.

Also, I forgot the "w" mode.

···

  while (data=file.read(N))
    f.write data
  end
end

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

11

careful, if you don't read the child will block when the pipe becomes full i
think. you might need to add

   file = File.open("mypdf.pdf")

   png =
     IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
       while (data=file.read(N))
         f.write data
       end
       f.close_write
       f.read
     end

not sure if that was obvious or not... sorry if it was.

-a

···

On Fri, 17 Nov 2006, Joel VanderWerf wrote:

Adam Groves wrote:

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file object (which has been uploaded from a web page form) to 'convert' and not just a path. I should have made this clearer in my original post.

Any ideas?

Untested, but maybe something like this?

file = File.open("mypdf.pdf")
IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
while (data=file.read(N))
   f.write data
end
end

--
my religion is very simple. my religion is kindness. -- the dalai lama

12

I was confused in several respects: I was thinking of a one-way pipe (but I forgot the "w"), in which case blocking wouldn't be a problem. But the one-way pipe would only be useful if the OP could put a filename in place of the "png:-".

The one-way pipe has the advantage that you can read(N) instead of read(), and keep memory bounded. Maybe it's not an issues for the OP, though.

···

ara.t.howard@noaa.gov wrote:

On Fri, 17 Nov 2006, Joel VanderWerf wrote:

Adam Groves wrote:

Hi Joel,

thanks for the speedy reply! The problem is, I need to pass on a file object (which has been uploaded from a web page form) to 'convert' and not just a path. I should have made this clearer in my original post.

Any ideas?

Untested, but maybe something like this?

file = File.open("mypdf.pdf")
IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
while (data=file.read(N))
   f.write data
end
end

careful, if you don't read the child will block when the pipe becomes full i
think. you might need to add

  file = File.open("mypdf.pdf")

  png =
    IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
      while (data=file.read(N))
        f.write data
      end
      f.close_write
      f.read
    end

not sure if that was obvious or not... sorry if it was.

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

13

huh. never really thought of it that way - good reason to do

   require 'tempfile'

   t = Tempfile.new Process.pid.to_s
   t.close

   cmd = "convert ... > #{ t.path }"

   # etc

cheers.

-a

···

On Fri, 17 Nov 2006, Joel VanderWerf wrote:

I was confused in several respects: I was thinking of a one-way pipe (but I
forgot the "w"), in which case blocking wouldn't be a problem. But the
one-way pipe would only be useful if the OP could put a filename in place of
the "png:-".

The one-way pipe has the advantage that you can read(N) instead of read(), and keep memory bounded. Maybe it's not an issues for the OP, though.

--
my religion is very simple. my religion is kindness. -- the dalai lama