GNU Parallel Bug Reports Alpha release of GNU Parallel 20110505

[Ole Tange]

The GNU Parallel 20110505 alpha release can be fetched at:
http://alpha.gnu.org/gnu/parallel/parallel-20110505.tar.bz2

Please test it thoroughly so we are sure nothing is broken.

So far GNU Parallel has been focused on replacing a single
for-loop. This alpha release introduces a way to replace nested
loops.

As example I will use the image manipulation program 'convert'. This
will convert foo.png to jpg with a size of 800 and JPEG-quality of 95.

convert -size 800 -quality 95 foo.png foo_800_q95.jpg

With a for-loop it can be done on a list of files:

time \
for file in *.png ; do
  convert -size 800 -quality 95 $file ${file##.JPG}_800_q95.jpg
done

Using GNU Parallel it looks like this:

time parallel convert -size 800 -quality 95 {} {.}_800_q95.jpg ::: *.png

To get the images in 3 different JPEG-qualities you can use a nested for-loop:

time \
for qual in 25 50 95 ; do
  for file in *.png ; do
    convert -size 800 -quality $qual $file ${file##.JPG}_800_q${qual}.jpg
  done
done

With GNU Parallel 20110505 you can do this:

time parallel convert -size 800 -quality 95 {1} {1.}_800_q{2}.jpg :::
*.png ::: 25 50 95

To get the 3 different JPEG-qualities in 2 different sizes you can use
a nest the for-loop even further:

time \
for size in 800 30 ; do
  for qual in 25 50 95 ; do
    for file in *.png ; do
      convert -size $size -quality $qual $file
${file##.JPG}_${size}_q${qual}.jpg
    done
  done
done

With GNU Parallel 20110505 you can do this:

time parallel convert -size {3} -quality {2} {1} {1.}_{3}_q{2}.jpg :::
*.png ::: 25 50 95 ::: 800 30

You can also provide the arguments in a file. This will do the same as above:

(echo 25; echo 50; echo 95) > qualities
ls *.png > png-files
(echo 800; echo 30) > sizes
time parallel convert -size {3} -quality {2} {1} {1.}_{3}_q{2}.jpg
:::: png-files qualities sizes

It is also possible to mix triple and quad colon. These will do the
same as above:

time parallel convert -size {3} -quality {2} {1} {1.}_{3}_q{2}.jpg
:::: png-files ::: 25 50 95 ::: 800 30

time parallel convert -size {3} -quality {2} {1} {1.}_{3}_q{2}.jpg
:::: png-files ::: 25 50 95 :::: sizes

The special file '-' reads from standard input. This will do the same as above:

ls *.png | time parallel convert -size {3} -quality {2} {1}
{1.}_{3}_q{2}.jpg :::: - ::: 25 50 95 :::: sizes

Please download
http://alpha.gnu.org/gnu/parallel/parallel-20110505.tar.bz2 and test
it thoroughly so we are sure nothing is broken.


/Ole