Not the most efficient solution but this is what springs to mind for me: seq 1000 | xargs printf '%04d_A.csv\n' | while read -r f; do test -f $f || echo $f

Not the most efficient solution but this is what springs to mind for me: seq 1000 | xargs printf '%04d_A.csv\n' | while read -r f; do test -f $f || echo $f; done