Bash: Terminate on Timeout/File Overflow while Executing Command

Question

I'm writing a mock-grading script in bash. It's supposed to execute a C program which will give some output (which I redirect to a file.) I'm trying to (1) make it timeout after a certain duration and also (2) terminate if the output file reaches a certain file size limit. Not sure how to go about either of these. Any help? Thanks.

Answer 1

There's a GNU coreutil command timeout to do timeouts.

Investigate ulimit -f 32 to set the maximum file size (to 16 KiB; it counts in 512 byte blocks).

Objection:

ulimit is [not] suitable because I have to create other files as well. I need to limit only one of them.

Counter: Unless the program must create a big file and a little file and you have to limit just the little file, you can use a sub-shell to good effect:

(
ulimit -f 32
timeout 10m -- command arg >file
)

The limit on file size is restricted to the commands in the sub-shell (which is marked by the pair of parentheses).

Answer 2

you can use timeout command eg

timeout -s 9 5s ./c_program > file

to check file size, you can stat the file, then do if/else

limit=1234 #bytes
size=$(stat -c "%s" file)
if [ "$size"  -gt "$limit" ] ;then
  exit
fi

see also here if you can't use these GNU tools, or here for some other inspirations.

Answer 3

This starts yourcommand, redirecting output via dd to youroutputfile and putting a limit of 10000000 bytes on it: dd will terminate and SIGPIPE will be sent to yourcommand

yourcommand | dd of=youroutputfile bs=1 count=10000000 &

This will wait 5 seconds and kill yourcommand if not already terminated:

sleep 5
kill %yourcommand