number and string manipulation in bash

Question

I wrote a little bash script (my first) that does the following:

sed -e 's/Alpha=0/Alpha=x/' -e 's/Beta=0/Beta=y/' <file.pov >tmpfile.pov povray Width=480 Height=360 +Itmpfile.pov +Ofile_x_y.png

everything works as intented but now I would like to pack these two lines in a loop for x=0:30:180 and y=0:30:90 (edit: I mean all possible combinations of x in {0,30,60,90,120,180} and y in {0,30,60,90}).

So for example for x=60 and y=30 the code should behave like this:

sed -e 's/Alpha=0/Alpha=60/' -e 's/Beta=0/Beta=30/' <file.pov >tmpfile.pov povray Width=480 Height=360 +Itmpfile.pov +Ofile_60_30.png

I am aware, it should not be too hard, but for some reason, I just couldnt work it out by myself.

Sorry to bother you with my newbie questions!

Edit your question to show the full set of expected output given those x and y values as it's not clear if you want the output to include all possible combinations of both or if they should be one-to-one matched, nor is it clear even what you mean by x=0:30:180 and and y=0:30:90. Are you starting at zero and incrementing both by 30 but stopping at 180 for x and 90 for y or something else and how do the values relate to each other? — Ed Morton
– Ed Morton, Commented Jul 6, 2015 at 16:35

ikrabbe · Accepted Answer · 2015-07-06 21:07:27Z

1

Use seq with for loops:

for x in `seq 0 30 180` do for y in `seq 0 30 90` do sed -e 's/Alpha=0/Alpha='$x'/' -e 's/Beta=0/Beta='$y'/' <file.pov >tmpfile.pov fn="file_${x}_${y}.png" povray Width=480 Height=360 +Itmpfile.pov +O${fn} done done

seq is a great tool even if you don't need the numbers

for i in `seq 10` do call_me_ten_times done

edited Jul 6, 2015 at 21:07

answered Jul 6, 2015 at 16:33

ikrabbe

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3 Comments

ikrabbe Over a year ago

I think there was a problem with the ${fn} using $x_$y. It tries to read $x_ so I changed that to ${x}_${y}. I tried the sed with a simple file containing Alpha=0 and Beta=0. But I forgot the first -e. Sorry. Now it works.

ikrabbe Over a year ago

I use shells without these number features {0..30..180}. So I learned to like seq.

ikrabbe Over a year ago

It doesn't matter for the example, but the for loop runs about 2 times faster than a read for big numbers.

Jason Hu · Accepted Answer · 2015-07-06 16:59:27Z

here is a tricky bash hack, but it helps to reduce two nested for loop into a single while loop:

while read x y; do sed -e 's/Alpha=0/Alpha='"$x"'/' -e 's/Beta=0/Beta='"$y"'/' <file.pov >"tmpfile${x}_$y.pov" done < <(echo {0..180..30}' '{0..90..30} | tr ' ' '\n' | paste - -)

the process substitution at last generates all combinations of the range you specified.

one remaining problem should be the output file name. since you are overwriting the file every time. i think it would be better if you make the filename changes as it goes. perhaps in my way.

thank you, it works like a charm! i dont use different output files because i clean them up after all the rendering is done anyways.

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