CODEWITHSUNDEEP
gnu-parallel
alfC
alfC

Reputation: 16242

How to pass variables to parallel command

How do I pass different values to a single parallel command:

I tried this:

parallel ::: 'X="aa"' 'X="bb"' ::: echo ${X}

which only prints two empty lines, as if the value of X is not set. I tried with echo $X with the same result.

I expected it to print

aa
bb

as if I had run sequentially:

echo "aa"
echo "bb"

Upvotes: 1

Views: 928

Answers (1)

Ole Tange
Ole Tange

Reputation: 33685

It is not entirely clear what you want run.

You clearly do not want:

X="aa" echo ${X}
X="bb" echo ${X}

because that outputs nothing.

Do you want:

X="aa"; echo ${X}
X="bb"; echo ${X}

In that case you can do one of:

parallel ::: 'X="aa";' 'X="bb";' ::: 'echo ${X}'
parallel {1}\;{2} ::: 'X="aa"' 'X="bb"' ::: 'echo ${X}'
parallel '{}; echo ${X}' ::: 'X="aa"' 'X="bb"'

However, the GNU Parallel way to do it would be to use the GNU Parallel replacement strings instead of $X:

parallel echo {} ::: aa bb

So if you want to run:

CXX="c++"; ID="c++"; cd ${ID}; ${CXX} main.cpp
CXX="/local/bin/nvcc"; ID="nvcc"; cd ${ID}; ${CXX} main.cpp

You would use :::+ :

parallel 'cd {2}; {1} main.cpp' ::: c++ /local/bin/nvcc :::+ c++ nvcc

Also: --dry-run is your friend, as it will show you what would be run, and that can often help understand the effect.

If you are new to GNU Parallel and prefer reading a book, buy GNU Parallel 2018 at http://www.lulu.com/shop/ole-tange/gnu-parallel-2018/paperback/product-23558902.html or download it at: https://doi.org/10.5281/zenodo.1146014

Read at least chapter 1+2. It should take you less than 20 minutes.

Upvotes: 1

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