I find appending to the same file in parallel scary: There are certain situations where it is safe to do, but there are sooo many situations where it is not safe:
# Generate files with a single very long line
parallel -j0 perl -e '\$a=\"1{}\"x10000000\;print\ \$a,\"\\n\"' '>' {} ::: {a..z}
rm -f out.par
# Grep for the single line in parallel - append to same file
parallel -j0 'grep 1 >> out.par' ::: {a..z}
# This ought to only give a single line for each letter
# But because of race condition some lines are split into two
parallel --tag 'grep {} out.par | wc -l' ::: {a..z}
rm out.par
# Do the same in serial (no race condition)
parallel -j1 'grep 1 >> out.par' ::: {a..z}
# Only a single line per letter
parallel --tag 'grep {} out.par | wc -l' ::: {a..z}
# Do the same in parallel but with serialized output (no race condition)
parallel -j0 grep 1 ::: {a..z} > out.par
# Only a single line per letter
parallel --tag 'grep {} out.par | wc -l' ::: {a..z}
So if I were you I would first change ./Run to output to stdout (standard output), so you can do:
./Run -t 1500 -2 500 > filename
# And in parallel:
parallel ./Run -t {2} -2 {1} :::: <(seq 500 500 600000) :::: <(seq 1500 5000 15000) > filename
To solve your original question we need to agree, that order does matter: It is unacceptable if the jobs are output in completely random order. Therefore we need --keep-order (-k).
parallel -k ./Run -t {2} -2 {1} :::: <(seq 500 500 600000) :::: <(seq 1500 5000 15000) > filename
Now we just need to make something that only runs if the first parameter is 11500:
parallel -k './Run -t {2} -2 {1}; if [ {2} -eq 11500 ]; then echo "";fi' :::: <(seq 500 500 600000) :::: <(seq 1500 5000 15000) > filename
I am not sure what you need it for, but you might want to take a look at --tag as that might be useful for you.
