Open Source and Free Software

could be that you are using > instead of >> to redirect output

> #for each iteration it'll overwrite the outputfile

>> #appends data to output file

rough and fast 'hackup' could look like

(checked on busybox) and dumps errors to stdout

for i in $(ls);do echo $i >>output.out && hexdump $i |head -4 >> output.out ;done

output.out will be
filename
hexoutput 4 lines
filename
hexoutput 4 lines

and so on

hope this helps (like i said, only tested on w32 system with busybox ash/sh) (all i had access to fast and dirty)