# Another IO.popen question **URL:** \ **Category:** ruby-talk\ **Created:** [16 November 2006 22:03 UTC](https://rubytalk.org/t/another-io-popen-question/33005 "2006-11-16T22:03:38Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Adam\_Groves](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@Adam\_Groves](https://rubytalk.org/u/Adam_Groves)\ **Post date:** [16 November 2006 22:03 UTC](https://rubytalk.org/t/another-io-popen-question/33005/1 "2006-11-16T22:03:38Z")
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/](http://www.ruby-forum.com/). ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [16 November 2006 22:09 UTC](https://rubytalk.org/t/another-io-popen-question/33005/2 "2006-11-16T22:09:37Z")
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 ---
**Author:** ![Tim\_Hunter4](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@Tim\_Hunter4](https://rubytalk.org/u/Tim_Hunter4)\ **Post date:** [16 November 2006 22:16 UTC](https://rubytalk.org/t/another-io-popen-question/33005/3 "2006-11-16T22:16:19Z")
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](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](http://www.simplesystems.org/RMagick/doc/image1.html#read) ---
**Author:** ![Adam\_Groves](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@Adam\_Groves](https://rubytalk.org/u/Adam_Groves)\ **Post date:** [16 November 2006 22:22 UTC](https://rubytalk.org/t/another-io-popen-question/33005/4 "2006-11-16T22:22:33Z")
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/](http://www.ruby-forum.com/). ---
**Author:** ![Adam\_Groves](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@Adam\_Groves](https://rubytalk.org/u/Adam_Groves)\ **Post date:** [16 November 2006 22:30 UTC](https://rubytalk.org/t/another-io-popen-question/33005/5 "2006-11-16T22:30:08Z")
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](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)](http://www.simplesystems.org/RMagick/doc/image1.html#read) 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/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [16 November 2006 22:39 UTC](https://rubytalk.org/t/another-io-popen-question/33005/6 "2006-11-16T22:39:41Z")
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 ---
**Author:** ![Tim\_Hunter4](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@Tim\_Hunter4](https://rubytalk.org/u/Tim_Hunter4)\ **Post date:** [16 November 2006 22:35 UTC](https://rubytalk.org/t/another-io-popen-question/33005/7 "2006-11-16T22:35:49Z")
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. ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [16 November 2006 22:48 UTC](https://rubytalk.org/t/another-io-popen-question/33005/8 "2006-11-16T22:48:22Z")
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 ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [16 November 2006 23:03 UTC](https://rubytalk.org/t/another-io-popen-question/33005/9 "2006-11-16T23:03:04Z")
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 ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [16 November 2006 23:09 UTC](https://rubytalk.org/t/another-io-popen-question/33005/10 "2006-11-16T23:09:15Z")
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 ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [16 November 2006 23:44 UTC](https://rubytalk.org/t/another-io-popen-question/33005/11 "2006-11-16T23:44:08Z")
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 ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [17 November 2006 00:52 UTC](https://rubytalk.org/t/another-io-popen-question/33005/12 "2006-11-17T00:52:32Z")
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 ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [17 November 2006 03:14 UTC](https://rubytalk.org/t/another-io-popen-question/33005/13 "2006-11-17T03:14:42Z")
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