Having trouble with multiple variables using read in a while loop

Question

Still learning and I'm getting lost with IFS=

#!/bin/bash
inotifywait -m -r --excludei '(.txt$|.old$|.swp$|.swx$|.swpx$|.zip$)' /path/to/watch -e create |
    while read path action file; do
        cd $path
        USER="$(stat -c %U $file)"
        echo "To: User <[email protected]>
CC: Support <[email protected]>
From: $USER <[email protected]>
Subject: $USER has Uploaded a new File

The user '$USER' uploaded the file '$file' to '$path'" >  /mnt/remote/ian/temp2.txt
    cat /path/to/temp/file.txt | ssmtp [email protected]
    rm /path/to/temp/file.txt
done

This was my first ever script and it works great as long as there are no spaces in the the file names that get uploaded. I've read some scripts that use IFS= 'whatever' to define the field separators but I don't want to mess around with this while it's in production; it works, but it annoys me when I can't get the username of the user who uploaded the file. Please give me a hint.

Since inotifywait's format strings don't support \0 -- the only character which can't legally exist in a filename -- there literally isn't a 100%-reliable solution possible. — Charles Duffy
– Charles Duffy, Commented Mar 30, 2015 at 21:33
BTW, note how I'm using double-quotes around any expansion of "$file" or "$path"? That's essential to avoid bugs; shellcheck.net will point out any places where you're skipping it. — Charles Duffy
– Charles Duffy, Commented Mar 30, 2015 at 21:38
BTW, are you sure you want create (flagging when a file is created, but not necessarily when content is done being written to it), as opposed to close_write? — Charles Duffy
– Charles Duffy, Commented Apr 1, 2015 at 15:25

Charles Duffy · Accepted Answer · 2015-04-02 16:17:58Z

This can be broken by an attacker who knows your implementation and wants to spoof arbitrary data (by creating filenames with newlines), but it's a rough first draft:

while IFS= read -r -d $'\n' path && IFS= read -r -d $'\n' file; do
    user=$(stat -c %U "$file")
    printf 'File %q created by %q in %q\n' "$file" "$user" "$path"
done < <(inotifywait --format $'%w\n%f\n' ~/tmp -r -e create)

I'd strongly suggest filing a ticket with upstream inotifytools requesting the ability use \0 in format strings.

Incidentally, this has already been brought up on the inotify-tools mailing list, where Stephane Chazelas offered a workaround:

nl="
"
inotifywait --syslog -e close_write -mr /tmp --format '%f///' |
  while IFS= read -r file; do
    while :; do
      case $file in
        (*///) file=${file%///}; break
      esac
      IFS= read -r extra || exit
      file=$file$nl$extra
    done

    something with "$file"

  done

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