I am running this:
cat /dev/urandom|hexdump| grep -i "ffff f" > random
and I get nothing in file random, it remains zero length after the command is interrupted.
How to make it writing output to a file?
I need to write a result to a file, which should contains output data like this:
021bc40 7724 d4f5 59ec bcbb ffff fd26 ab3c 9b7c
03a9100 b3a5 8601 fa33 ffff f23c 4326 2e7f 0c8a
0449810 e459 d5af 4e11 ffff fc55 8660 9efb 3c9b
4 Answers
Use the --line-buffered option for grep (and also get rid of the useless cat):
hexdump /dev/urandom | grep --line-buffered -i "ffff f" > randomThis way the output is not buffered but every line put into random immediately. I would also recommend to use tee in your pipe to see how many lines have been produced:
hexdump /dev/urandom | grep --line-buffered -i "ffff f" | tee randomYour file is empty because the process is interrupted before the file is written to disk. That is how redirection works. As a workaround, try this:
script -c 'cat /dev/urandom|hexdump|grep -i "ffff f"' -f randomThis will basically write all screen output to the file.
1cat /dev/urandom|hexdump or hexdump /dev/urandom writes continuously to the stdout and if you press Ctrl+C nothing will be executed after this. But you can limit the output with head
hexdump /dev/urandom | head -n1000000 | grep "ffff f" > random this will grep in the first 1000000 lines of the output and writes the result to a file.
You will need to write the output of cat /dev/urandom | hexdump to a file before you execute it the next time. The script below should accomplish what you are trying:
cat /dev/urandom | hexdump | while IFS= read -r line; do printf '%s\n' "$line" >> random; doneIFS is used to split the output into lines here.
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