How to use inotifywait to watch a directory for creation of files of a specific extension

I have seen this answer.

You should consider using inotifywait, as an example:

inotifywait -m /path -e create -e moved_to |
    while read path action file; do
        echo "The file '$file' appeared in directory '$path' via '$action'"
        # do something with the file
    done

My question is that, the above script watches a directory for creation of files of any type, but how do I modify the inotifywait command to report only when a file of certain type/extension is created (or moved into the directory) – e.g. it should report when any .xml file is created.

WHAT I TRIED:

I have run the inotifywait --help command, and have read the command line options. It has --exclude <pattern> and --excludei <pattern> commands to EXCLUDE files of certain types (by using regEx), but I need a way to INCLUDE just the files of a certain type/extension.

Answers:

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Method 1

how do I modify the inotifywait command to report only when a file of
certain type/extension is created

Please note that this is untested code since I don’t have access to inotify right now. But something akin to this ought to work:

inotifywait -m /path -e create -e moved_to |
    while read directory action file; do
        if [[ "$file" =~ .*xml$ ]]; then # Does the file end with .xml?
            echo "xml file" # If so, do your thing here!
        fi
    done

Method 2

Whilst the double-negative approach of the previous answer is a nice idea since (as TMG noted) it does indeed shift the job of filtering to inotifywait, it is not correct.

For example, if a file ends in as then it will not match [^j][^s]$ because the final letter s does not match [^s], therefore it will not be excluded.

In Boolean terms, if S is the statement:

“the final letter is s”

and J is the statement:

“the penultimate letter is j”

then the value of the --exclude parameter should semantically equate to not(J and S), which by De Morgan’s laws is not(J) or not(S).

Another potential problem is that in zsh, $path is a built-in variable representing the array equivalent of $PATH, so the while read path ... line will completely mess up $PATH and cause everything to become unexecutable from the shell.

Therefore the correct approach is:

inotifywait -m --exclude "[^j].$|[^s]$" /path -e create -e moved_to |
    while read dir action file; do
        echo "The file '$file' appeared in directory '$dir' via '$action'"
    done

Note the . which is needed after [^j] to ensure that the match is applied in the penultimate position, and also that the | character (representing the boolean OR mentioned above) should not be escaped here because --exclude takes POSIX extended regular expressions.

However, please see and upvote @ericcurtin’s answer which for newer versions of inotifywait is a far cleaner approach.

Method 3

--include and --includei are actual options, in the master version of the binaries at least:

https://github.com/inotify-tools/inotify-tools/tree/master

Method 4

Use a double negative:

inotifywait -m --exclude "[^j][^s]$" /path -e create -e moved_to |
    while read path action file; do
        echo "The file '$file' appeared in directory '$path' via '$action'"
    done

This will only include javascript files

Method 5

Starting with inotifywait version 3.20.1 you can use an --include option.

inotifywait example with --include

Here’s an example that uses --include to run a script when a wav file is added to a directory.

#!/bin/sh

# Usage
#
# Call the script with the directory you want to watch as an argument. e.g.:
# watchdir.sh /app/foo/
#
#
# Description:
# Uses inotifywait to look for new files in a directory and process them:
# inotifywait outputs data which is passed (piped) to a do for subcommands.
#
#
# Requirements:
# Requires inotifywait which is part of inotify-tools.
# e.g. yum install -y inotify-tools or apt-get install -y inotify-tools.
#
#
# See also:
# https://linux.die.net/man/1/inotifywait
# https://github.com/inotify-tools/inotify-tools/wiki#info
# (Might be interested in pyinotify too.)


echo "Watch $1 for file changes..."


# Be careful not to confuse the output of `inotifywait` with that of `echo`.
# e.g. missing a `` would break the pipe and write inotifywait's output, not
# the echo's.
inotifywait 
  $1 
  --monitor 
  -e create 
  --timefmt '%Y-%m-%dT%H:%M:%S' 
  --format '%T %w %f %e' 
  --include ".wav" 
| while read datetime dir filename event; do
  echo "Event: $datetime $dir$file $event"
  echo "Now, we could pass $datetime $dir $filename and $event to some other command."

  echo "Here's the extensionless filename:" ${filename%.*}
  echo "And the extension if needed:" ${filename##*.}

  python3 /app/phono.py --custom $dir$filename $dir${filename%.*}.txt /tmp/${filename%.*}
done


# --format:
#   %T  Replaced with the current Time in the format specified by the --timefmt option, which should be a format string suitable for passing to strftime(3).
#   %w  This will be replaced with the name of the Watched file on which an event occurred.
#   %f  When an event occurs within a directory, this will be replaced with the name of the File which caused the event to occur. Otherwise, this will be replaced with an empty string.
#   %e  Replaced with the Event(s) which occurred, comma-separated.
#   %Xe Replaced with the Event(s) which occurred, separated by whichever character is in the place of 'X'.
#
# There's no --include option, but there's --exclude, which can be used to the same effect as an include.


# test the script by creating a file in the watched directory, e.g.
# touch /app/foo/file1.wav # will trigger the script
# touch /app/foo/file1.txt # will not trigger the script

Installing (or compiling) inotify-tools

inotifywait is part of inotify-tools. You can install it via the usual way, e.g.:

apt-get install -y inotify-tools

or

yum install -y inotify-tools

But if only older versions are available from the repos, you may want to compile from source. If so:

cd /tmp/inotify-tools/
wget https://github.com/inotify-tools/inotify-tools/releases/download/3.20.2.2/inotify-tools-3.20.2.2.tar.gz
tar xzvf inotify-tools-3.20.2.2.tar.gz
cd inotify-tools-3.20.2.2
./configure --prefix=/usr --libdir=/lib64
make
make install

Method 6

In my case I was trying to filter the output of inotifywait using something like grep, in order to wait for the creation of a single file with a particular extension. The trouble with this approach is that grep will just hang.

For some reason a SIGPIPE signal is either not sent, or not processed by inotifywait. I found this question, which ran into the same issue I had, and process substitution can be used as a workaround:

grep -E .*iso -m1 < <(inotifywait -qm -e create .)

Process substitution does not work in certain shells (eg. sh), so this does not work in every case.

From the other answers given, I could not find the –include option. I will likely be experimenting with –exclude.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0