On Linux:
printf -- '-get data_%d.txt\
' $(seq 1 3 100) | sftp -b - user@example.com
On BSD (with no `seq(1)` in sight):
printf -- '-get data_%d.txt\
' $(jot 100 1 100 3) | sftp -b - user@example.com
On Linux:
printf -- '-get data_%d.txt\
' $(seq 1 3 100) | sftp -b - user@example.com
On BSD (with no `seq(1)` in sight):
printf -- '-get data_%d.txt\
' $(jot 100 1 100 3) | sftp -b - user@example.com