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linuxbashterminalpipeecho

Pipe an output into echo as an variable for calculation

My goal is to divide 2 text files, each containing a single integer, but limiting the answer to 2 decimal places.

I managed to do it with paste total.txt count.txt | awk '{printf "%.2f\n", $1/$2}'

But I saw another way of using echo 'scale=2; <calculation here>' | bc -l

I couldn't figure out how to pass the numbers from the previous pipe to echo as an variable/argument, I tried use xargs but didn't know how to reference it.

I tried this: paste -d/ total.txt count.txt | bc -l | xargs echo 'scale=2;' | bc -l
and this: echo 'scale=2; $(paste -d/ total.txt count.txt)/1' | bc -l

My goal is to pipe output into echo as a variable for calculation or use commands inside echo , thank you.

Solution

  • What I would do:

    total.txt = 100    
count.txt = 3  

    bc <<< "scale=2; $(paste -d '/' total.txt count.txt);"
33.33

    or

    echo "scale=2; $(paste -d '/' total.txt count.txt);" | bc -l
33.33

    Your attempt:

    echo 'scale=2; $(paste -d/ total.txt count.txt)/1' | bc -l

    was close, but with single quotes, you prevent the shell to expand the $(command substitution).

    Learn how to quote properly in shell, it's very important :

    "Double quote" every literal that contains spaces/metacharacters and every expansion: "$var", "$(command "$var")", "${array[@]}", "a & b". Use 'single quotes' for code or literal $'s: 'Costs $5 US', ssh host 'echo "$HOSTNAME"'. See
    http://mywiki.wooledge.org/Quotes
    http://mywiki.wooledge.org/Arguments
    https://web.archive.org/web/20230224010517/https://wiki.bash-hackers.org/syntax/words
    when-is-double-quoting-necessary