Bash Shell Script – Split Input for Different Commands and Combine Results

bashpipeprocess-substitutionshell-scripttext processing

I know how to combine the result of different command 

paste -t',' <(commanda) <(commandb)

I know pipe same input to different command

cat myfile | tee >(commanda) >(commandb)

Now how to combine these command? So that I can do

cat myfile | tee >(commanda) >(commandb) | paste -t',' resulta resultb

Say I have a file

myfile:

1
2
3
4

I want to make a new file 

1 4 2
2 3 4
3 2 6
4 1 8

I used 

cat myfile | tee >(tac) >(awk '{print $1*2}') | paste

would gives me result vertically, where I really want paste them in horizontal order.

Best Answer

When you tee to multiple process substitutions, you're not guaranteed to get the output in any particular order, so you'd better stick with

paste -t',' <(commanda < file) <(commandb < file)

Assuming cat myfile stands for some expensive pipeline, I think you'll have to store the output, either in a file or a variable:

output=$( some expensive pipeline )
paste -t',' <(commanda <<< "$output") <(commandb <<< "$output")

Using your example:

output=$( seq 4 )
paste -d' ' <(cat <<<"$output") <(tac <<<"$output") <(awk '$1*=2' <<<"$output")

1 4 2
2 3 4
3 2 6
4 1 8

Another thought: FIFOs, and a single pipeline

mkfifo resulta resultb
seq 4 | tee  >(tac > resulta) >(awk '$1*=2' > resultb) | paste -d ' ' - resulta resultb
rm resulta resultb

1 4 2
2 3 4
3 2 6
4 1 8
Related Question