find -exec syntax: bug in find?

mfcarroll · 06-20-2007, 01:53 PM

I'm writing a small bash script to convert a pdf into a series of png images (one for each page of the pdf). This works almost perfectly:

Code:

#!/bin/bash
OUT=./pdf_png_convert/
mkdir $OUT
pdftoppm -r 300 $1 $OUT`basename $1 .pdf`
exit
find $OUT -iname *.PPM -exec convert '{}' `basename '{}' .ppm`.png \;
find $OUT -iname *.PPM -exec rm '{}' \;
mv $OUT/* .

However, the reduction of the final image name to .png using basename doesn't work. I'm left with .ppm.png files.

I know I can work around this quite easily by doing the convert then rename afterwards to fix the extensions, but this seems like it might be a bug in find. I reduced this to the following test case:

Code:

$ find -iname *.PPM -exec basename {} .ppm \;
test-000001

vs.

Code:

$ find -iname *.PPM -exec echo `basename {} .ppm` \;
./test-000001.ppm

I'm no bash guru, but is this a bug in find, or just my understanding of the -exec syntax? Any thoughts?

Thanks
Matthew

wjevans_7d1@yahoo.co · 06-20-2007, 02:32 PM

The `basename '{}'` is done by bash before the execution of the find; basename returns the string {}, and bash then substitutes {} for `basename '{}' .ppm`.

It took me a few minutes to see this.

mfcarroll · 06-20-2007, 02:42 PM

Of course... silly me for not seeing that. Thanks.

Code:

$ echo `basename {} .ppm`
{}

So, the question, now, is "is there any way to do that in a single line" - that kind of thing bugs me; I feel like there must be an elegant way to do that as part of the -exec. Maybe there's a bash guru out there with an answer?

wjevans_7d1@yahoo.co · 06-21-2007, 01:56 PM

If you're willing to have a rather long "single line", and you're willing to forego the -exec, how about this?

Code:

( find $OUT -iname '*.PPM' > temp1) ; (sed -e 's/...$/png/' temp1 > temp2) ; (sed -e 's/^/convert /' temp1 > temp3 ) ; (paste temp3 temp2 > temp4); . temp4; rm temp1 temp2 temp3 temp4

dawkcid · 06-21-2007, 02:15 PM

Code:

... -exec sh -c 'convert {} $(basename {} .ppm).png' \;

Or

Code:

for f in $(find $OUT -iname *.PPM); do
  tmp=${f##*/}
  convert $f ${tmp%.*}.png && rm $f
done

mfcarroll · 06-21-2007, 07:13 PM

Thanks everyone. dawkcid's solution seems the cleanest - I've done that in bash that I understand. Here's the final script:

Code:

#!/bin/bash
OUT=./pdf_png_convert/
mkdir $OUT
pdftoppm -r 300 $1 $OUT`basename $1 .pdf`
for f in `find $OUT -iname *.PPM`; do
   BASE=`basename $f .ppm`
   convert $f $OUT/$BASE.png && rm $f
done
mv $OUT/* .
rmdir $OUT