running bash pipe commands in background with & ampersand

Question

time for i in `ls /tmp/chunk*`; do (cat $i | tr ' ' '\n' | sort | uniq > /tmp/line${i:10}) & ;done
bash: syntax error near unexpected token `;'

Whats the syntax error in the above command? I also tried using {} and ended the piped commands with ;. But same error shows up ...

Answer 1

You should put the & inside the (), if you want to run all the jobs in parallel in the background.

time for i in `ls /tmp/chunk*`; do
  (cat $i | tr ' ' '\n' | sort | uniq > /tmp/line${i:10} &)
done

Answer 2

You can include the & in braces:

time for i in `ls /tmp/chunk*`; do
  {(cat $i | tr ' ' '\n' | sort | uniq > /tmp/line${i:10}) &};
done

Answer 3

& is a separator and so is redundant with ; I.E. remove the final ;

for i in /tmp/chunk*; do tr ' ' '\n' <$i | sort -u > /tmp/line${i:10}& done