Script to monitor a folder and compress the content

Question

We have a Debian Squeeze server where we upload files through SFTP, and I wrote this script to automatically compress uploaded files.

The script is scheduled through a cron job in an unprivileged user's crontab.

As of now, the script works and does its job.

But I'm pretty novice to Bash scripting, and I'm wondering if it has any major flaws. (e.g. If the file name contains " what happens? Does it have security flaws?)

Also, am I doing it right, or there are better ways to do it?

#!/bin/bash

# Use the newline character
# as the field separator.
IFS=$'\n'

# The folder to watch.
dir="/path"

# Get the folder's content, recurively.
for item in $(find "${dir}")
do

        # If the item is a regular file.
        if [ -f "${item}" ]
        then

                # Check if the file is in use 
                # by someone else. E.g. The SFTP
                # daemon because the user is still
                # uploading it.
                lsof -n "${item}" > /dev/null

                # If no one is using the file.
                if [ "$?" -ne 0 ]
                then

                        # Get the file extension.
                        ext=$(echo "${item}" | awk -F "." '{ print $NF }')

                        # If the file is not a zip archive
                        # and does not exists a zip archive for it
                        if [ "${ext}" != "zip" -a ! -f "${item}.zip" ]
                        then
                                # Create the zip archive.
                                zip "${item}.zip" "${item}" > /dev/null
                        fi

                fi

        fi

done

Answer 1

Slightly different than @kojiro's answer, using find for everything:

find /path \
     -type f \
     ! -iname "*.zip" \
     ! -exec /usr/sbin/lsof -n "{}" \; \
     ! -exec test -f "{}.zip" \; \
     -exec zip -q "{}.zip" "{}" \; \
     -exec rm "{}" \;

(last step only if the removal of the original is required).

Answer 2

Almost all the work you've done can be done by find directly. It's efficient at eliminating based on your parameters, and can pass a tailored list of arguments to bash for final zipping.

#!/bin/bash

# The folder to watch.
dir="/path"

# You shouldn't ever loop over for x in $(find …) this way, because it can break easily;
# however, find offers several options itself to give you another approach:

find "$dir" \
    -type f \ # If the item is a regular file
    ! -iname '*.zip' \ # If the filename does not end with zip (case-insensitive)
    ! -exec lsof -n {} \; \ # If the file is not in use by someone else
    -exec bash -c '
        # back to bash for this part
        # loop over the parameters passed to bash, which should only be interesting files
        for item
        do
            # Create the zip archive only when one does not exist
            [[ -f ${item}.zip ]] || zip "${item}.zip" "${item}" > /dev/null
        done
    ' _ {} + # pass all the found files to bash to process.

Edited to reflect that IFS isn't being used anymore.

Answer 3

I don't see why it needs to be so complicated. You also risk all sorts of problems if the files happen to contain newlines (and this isn't just a theoretical, I've seen it happen, especially when copying text to file managers that don't chomp filenames when renaming).

A note: globstar requires bash4.

#!/bin/bash
shopt -s nullglob globstar extglob
for file in /path/**/!(*.zip); do
    [[ -f $file && ! -e $file.zip ]] && lsof -n "$file" >/dev/null || continue
    zip -q "$file"{.zip,}
done