command line arguments fed from an array

问题

I'd like to perform a complicated bash command, using data fed from a long array as arguments. I guess it has to use a subshell in some way.

For example, instead of the workable convert -size 100x100 xc:black -fill white -draw "point 1,1" -draw "point 4,8" -draw "point 87,34" etc etc etc image.png

I want to employ a different logic where the arguments are given in the same command, more like

convert -size 100x100 xc:black -fill white $(for i in 1,1 4,8 87,34 etc etc; -draw "point $i"; done) image.png which doesn't work, as the $i is interpreted as a command insted of an argument.

Please note that "for i in ...; do convert ...$i...; done" will not work. The -draw "point x,y" series of arguments must be in the same single run convert command, as convert doesn't accept -draw parameter in existing images.

回答1:

Build up an array of -draw arguments first.

for pt in 1,1 4,8 87,34; do
    points+=(-draw "point $pt")
done
convert -size 100x100 xc:black -fill white "${points[@]}" image.png

回答2:

You can keep your command line short and clean by pumping MVG drawing commands into convert via its stdin by using the @ file specifier followed by a dash representing stdin like this:

for i in 1,1 4,8 87,34; do 
   echo point $i
done | convert -size 100x100 xc:red -draw @- result.png

Or, if you have an array called points:

points=(1,1 4,8 87,34)

printf "point %s\n" ${points[@]} | convert -size 100x100 xc:red -draw @- result.png

回答3:

Try to use expansion instead of subshell like this:

echo -draw\ \"point\ {1\,1,2\,2,3\,3}\"

produces this output:

-draw "point 1,1" -draw "point 2,2" -draw "point 3,3"

回答4:

What about using printf to expand the content?

points=(1,1 4,8 87,34)
printf -- '-draw "point %s" ' ${points[@]}

returns the following string (without a new line at the end):

-draw "point 1,1" -draw "point 4,8" -draw "point 87,34"

You can say:

points=(1,1 4,8 87,34)
convert ... "$(printf -- '-draw "point %s" ' ${points[@]})" image.png
#           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This way, you store the points in an array and printf "delivers" it to the convert command.

来源：https://stackoverflow.com/questions/36863888/command-line-arguments-fed-from-an-array

标签

bash

for-loop

parameter-passing

imagemagick-convert