CODEWITHSUNDEEP
bashshellwhile-loopinotify
TyeolRik
TyeolRik

Reputation: 484

inotifywait ignore while loop

I am having trouble with using inotifywait properly.

My environment is CentOS 8 Stream with i7-9700

test.sh

#!/bin/bash

inotifywait -e modify ./test.txt |
while read dirname eventlist filename
do
  echo "Event catch!"
done

echo "I am doing next thing"

output in terminal(stdout)

[root@ceph examples]# sh test.sh
Setting up watches.
Watches established.
I am doing next thing

What I expect?

I expect that my script print the line, "Event catch!". As you can see, my bash script ignore all while loop block and just print "I am doing next thing".

Upvotes: 1

Views: 408

Answers (1)

Léa Gris
Léa Gris

Reputation: 19545

The normal behavior of inotifywait is to exit after it has captured an event.

If you want inotifywait to keep monitoring events, you have to use the -m option switch.

Also in your script, you read 3 arguments from the output if inotifywait whereas only 2 might be returned if it has a single event. You may use the --format option to keep a predictable output format.

#!/bin/sh

inotifywait -m -e modify ./test.txt |
while read -r filename eventlist
do
  printf 'Event catch!\nfilename=%s, eventlist=%s\n' "$filename" "$eventlist"
done

printf %s\\n "I am doing next thing"

If you want to exit inotifywait, you just kill the parent process from the pipe.

Example:

#!/bin/sh

max_events=2
inotifywait -m -e modify ./test.txt |
while read -r filename eventlist
do
  printf 'Event catch!\nfilename=%s, eventlist=%s\n' "$filename" "$eventlist"
  max_events=$((max_events - 1))
  [ 0 -eq "$max_events" ] && kill $$
done

printf %s\\n "I am doing next thing"

And now with Bash arrays for events and reading a controlled format:

#!/bin/bash

max_events=2
while
  # Reads file name
  read -r -d '' filename &&
  # and reads event list in an array
  read -r -a eventlist
do
  declare -p filename eventlist
  printf 'Event catch!\nfilename! %s\neventlist: %s\n' "$filename" \
    "${eventlist[*]}"
  ((--max_events)) || break
done < <(
  inotifywait --format '%w%0%e' --monitor --event MODIFY ./test.txt
)

printf %s\\n "I am doing next thing"

Upvotes: 3

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