linux - how to backup stdout of running shell script -

here short example of problem

short script writes every 10 seconds test stdout

> cat write.sh #!/bin/sh while [ 1 ];do echo test sleep 10 done

and here how execute it, redirect stdout file named output.txt

./write.sh > output.txt

now, script should run "forever", meantime fills output.txt

we looking way backup output.txt without restart script. moreover, looking implicit solution, script won't aware file backed up.

of course once remove file (e.g. compress it) process (script) lose track of file , stop writing. if backup file (compress) , return file using touch script no long able reattach file.

for example:

mv test_file.txt test_file111.txt

rm test_file111.txt

> lsof | grep write write.sh 2644 ronnyr 1w reg 253,1 36 106059124 /home/ronnyr/test_file111.txt (deleted)

> touch test_file111.txt write.sh 2644 ronnyr 1w reg 253,1 36 106059124 /home/ronnyr/test_file111.txt (deleted)

if want alter or truncate output file use >> this:

./write.sh >> output.txt # take backup cp -p output.txt /path/backup/ # truncate stdout file > output.txt 

due use of >> (append) ./write.sh keep writing output @ end of file , remain unaffected when truncate output file.