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I have a folder full of files with a .dot extension like this:

a.dot
b.dot
c.dot

I want to go through all the files in this folder and run a command on them such as this:

dot -Tpdf a.dot -o a.pdf
dot -Tpdf b.dot -o b.pdf
dot -Tpdf c.dot -o c.pdf

I am guessing that I need to use the vertical bar and do a command like this:

ls *.dot | dot -Tpdf ... -o ....pdf

But I don't know how to make the pipe place each file onto the middle part only. Should I be using xargs? Furthermore, how to strip the extension then also place it onto the second part. If I could be at least pointed in the right direction (which shell command to use) it would help me very far along the way to figuring this out.

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Do not parse the output of ls. The shell performs wildcard expansion (e.g. of *.dot into a.dot b.dot c.dot); ls is a tool intended for humans, when you want to display file attributes (size, date, etc.). –  Gilles Feb 27 '12 at 2:09

3 Answers 3

up vote 6 down vote accepted

Use

for i in *.dat ; do dot -Tpdf "$i" -o "$(basename "$i" dot)pdf" ; done

EDIT: Correct handling of filenames with whitespaces.

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@Peter.O BTW, my origin answer without quotes works correctly in zsh, which I use, even for filenames with whitespaces. –  jofel Feb 23 '12 at 16:58
    
Thanks for pointing that out. In general, unless specifically stated, as you have now done, it is typically better to present the most portable syntax. POSIX being the definitive standard... –  Peter.O Feb 23 '12 at 22:45

xargs is another method to iterate over a set of filenames. However, you don't have the same flexibility as a for-loop to manipulate the filename in each iteration:

ls *.dot | xargs -n1 -I FILE echo dot -Tpdf FILE -o FILE.pdf

will result in

dot -Tpdf a.dot -o a.dot.pdf
dot -Tpdf b.dot -o b.dot.pdf
dot -Tpdf c.dot -o c.dot.pdf
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If you are a fan of awk and sed you can also achieve this with

ls *.dot | awk '{print("dot -Tpdf "$1" -o "$1)}' | sed 's/.dot/.pdf/2' | sh
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