How to write a loop in shell for graphicsmagick?

Question

I managed (with the help of SO) to make perfect png-snippets from a pdf file with graphicsmagick. My pdf contains text and formula each "snippet" on a single page. My command trims the content of a page to the very content and finally scales this up to 2000 pixel width.

Untill now, I need to repeat that command for each single page in every pdf. I am wondering how to automate this. I think I could try a loop for the repetition of the command for every page i untill the last page.

Assume file1.pdf is in my current working directory.

gm convert -density 300x300 file1.pdf[0] -trim -resize 2000x file1_page1.png
gm convert -density 300x300 file1.pdf[1] -trim -resize 2000x file1_page2.png
gm convert -density 300x300 file1.pdf[2] -trim -resize 2000x file1_page3.png
...

How can I set a counter and run a loop for every page in my document?

Mark Setchell · Accepted Answer · 2019-08-13T13:01:10.323

4

You are in luck. GraphicsMagick knows how to do that for you:

gm convert -density 300x300 input.pdf -trim -resize 2000x +adjoin output-%d.png

If you are ok using ImageMagick instead, you can set the starting output file number to 1 instead of 0 and don't need the -adjoin:

convert -density 300x300 input.pdf -scene 1 -trim -resize 2000x output-%d.png

Or, if you want them all done in parallel, use GNU Parallel:

parallel gm convert -density 300x300 {} -trim -resize 2000x output-{#}.png  ::: $(identify input.pdf | awk '{print $1}')

edited Aug 13 '19 at 13:01

answered Aug 13 '19 at 12:44

Mark Setchell

191,897
31
273
432

woah, that's much better than my answer. – JUSHJUSH Aug 13 '19 at 12:49
@JUSHJUSH There's more than one way to do it - and the question did ask for a loop, so technically yours is more correct than mine ;-) – Mark Setchell Aug 13 '19 at 12:50
I once more trapped into the XY-Problem. Asking kind of the wrong sub-routine for the job. First version works perfectly :) – Marco Aug 13 '19 at 13:06

JUSHJUSH · Answer 2 · 2019-08-13T11:39:09.533

2

for file in *.pdf
do
    pages=$(identify "$file" | wc -l)
    for (( i=0; i<$pages; i++ ))
    do
        name=$(sed "s/\.pdf$/$i.png/g" <<< "$file");
        gm convert -density 300x300 "$file[$i]" -trim -resize 2000x "$name"
    done
done

Try this one. It will convert every page in every *.pdf file to .png.

edited Aug 13 '19 at 11:39

answered Aug 13 '19 at 11:03

JUSHJUSH

367
1
11

Hi Jushjush, how should I execute this loop? I saved it to a loop.sh and tried to run in terminal. I did nothing. Should I add some #bash line? I'm new to shell scripting. – Marco Aug 13 '19 at 11:52
just use `bash loop.sh`. You have to be in the same directory as your pdf files. – JUSHJUSH Aug 13 '19 at 12:01
@MarcoDoe Please, check if `identify file1.pdf | wc -l` returns number of pages in your shell. – JUSHJUSH Aug 13 '19 at 12:03
Puh I really try, but cannot use the `identify` command. `bash loop.sh` gives errors, it says e.g. "line 1 $'\r': command not found$." – Marco Aug 13 '19 at 12:34
@MarcoDoe The problem with 'line 1 $\r' is probably linked with using windows. Try to run command `dos2unix loop.sh`, then run script. Also, do you have any other program to check number of pages in your pdf files? I think 'identify' program is part of imagesmagick package. – JUSHJUSH Aug 13 '19 at 12:38
Oh yes, I have Ubuntu shell on Windows 10. I created a sh with text editor. That probably crashed something. I converted with `dos2unix` line1 is now ok. But running the script still says "line 4: identify not found". It's a command from gm right? Do I have to put this in front of it? – Marco Aug 13 '19 at 12:44
@MarcoDoe Try to install imagemagick. If i remember correctl `sudo apt-get install imagemagick` should do the work. – JUSHJUSH Aug 13 '19 at 12:46
It gives new errors each time: "identify -im6.q16: not authorized @ error/constitute.c/ReadImage/412" more crypthic than ever. I will opt for the pure gm solution. Thanks Jush for the loop-structure, I will get it run one day :) – Marco Aug 13 '19 at 13:09

How to write a loop in shell for graphicsmagick?

2 Answers2