CODEWITHSUNDEEP
linuxbashcopy-pastetail
Shah9il
Shah9il

Reputation: 61

Self stopping tail operation

I needed some help for following:

In a menu a tail operation will be carried out and then after a certain output the tail will get terminated and we will get back to the menu.

tail -f server.log |
  grep "Started successfully with " &&
  echo "it is working" ||
  echo "not working"

Can anyone help me to have a self-closing tail command?

Upvotes: 3

Views: 517

Answers (2)

mklement0
mklement0

Reputation: 437688

@anubhava's answer works, but there is no need for awk:

The key is to use grep with -m1, which makes it return once a match is found, at which point the tail process can be killed:

tail -f server.log | 
  { grep -m1 "Started successfully with " && pkill -P $$ -x tail; }
  • -P $$ (considers only child processes of the current shell) and -x (matches process name exactly) ensure that only the tail process of interest is killed.
  • You could also use a subshell (...) instead of command grouping { ...; } (slightly less efficient).
  • If the string is not found, grep only returns in the event that tail is externally killed - to report this case, add a || clause; e.g., || echo 'ERROR: tail -f was killed' >&2

Upvotes: 3

anubhava
anubhava

Reputation: 785126

You can do:

tail -f server.log | awk '/Started successfully with/{print "it is working"; system("pkill tail"); exit}'

There is no case of printing "not working" since you're using tail -f and you never know for how long your search string isn't there.

Upvotes: 2

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