jr@saturn:~> cat `which rigol-screenshot `
#!/bin/sh
echo ':disp:data?' | netcat 192.168.4.52 5555 | dd bs=1M iflag=skip_bytes skip=11 of=$1
echo $?
jr@saturn:~> rigol-screenshot xxx.bmp
0+903 Datensätze ein
0+903 Datensätze aus
1152057 Bytes (1,2 MB) kopiert, 2,98393 s, 386 kB/s
0

#!/bin/bash
# usage: rigol-snapshot <filename_with_wellknown_imagefile_extension>
#        e.g.: rigol-snapshot pics/test.jpg
#   fetches a bmp formatted screenshot picture from Rigol DS1000 series, via ethernet
# TODO: proper handling of broken connection to Rigol, check netcat / read return code

RIGOL_IP=192.168.4.52   # adapt to your local situation, I used fixed DHCP IP for rigol in my router
set -e -u #might improve the TODO error handling as mentioned above. untested!!

echo ':disp:data?' | netcat -w 1 $RIGOL_IP 5555\
 | (shopt -s extglob;\
    read -N 1 -t 0.1 magichash;
    read -N 1 -t 0.1 lenofnum; 
    read -N $lenofnum -t 0.1 numofbytes; 
    head -c ${numofbytes##*(0)} ; 
    echo "magic: $magichash; len: $lenofnum; bytes: ${numofbytes##*(0)}" >&2\
   )\
 | convert bmp:- $1
echo "returncode: $?" >&2