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Ian
Asked: 2011-04-12 23:07:10 +0800 CST

Using wget to save sequential files as well as renaming the file extension

  • 772

I run a cron job that requests a snapshot from a remote webcam at a local address:

wget http://user:[email protected]/snapshot.cgi

This creates the files snapshot.cgi, snapshot.cgi.1, snapshot.cgi.2, each time it's run.

My desired result would be for the file to be named similar to file.1.jpg, file.2.jpg. Basically, sequentially or date/time named files with the correct file extension instead of .cgi.

Any ideas?

wget

2 Answers

  1. Best Answer

    You could probably torture wget into doing it, but why bother? Try

    wget http://user:[email protected]/snapshot.cgi
mv snapshot.cgi snapshot-`date +%Y-%m-%d-%H%M%S`.jpeg

    This should create date-and-time stamped images like snapshot-2011-04-12-081649.jpeg. Will that do?

    Edit: OK, not too much torturing is required:

    wget -O snapshot-`date +%Y-%m-%d-%H%M%S`.jpeg http://user:[email protected]/snapshot.cgi

    But most of me still prefers the UNIX way of doing it with small, discrete tools.

    • 4

  2. You can do this with a simple bash loop and the -O option in wget.

    Something like this:

    i=0
while 1
do
  # increment our counter
  ((i++))
  # get the file and save it
  wget -O file.$i.jpg http://user:[email protected]/snapshot.cgi
  # presumably you want to wait some time after each retrieval
  sleep 30
done

    One obvious annoyance is that if you already have a file.1.jpg in the directory and you start this script, it will be overwritten. To deal with that, you first need to find all the existing file.N.jpg files, find the largest value for N, and start at N+1. Here's an incredibly braindead way to do that:

    # find the last sequential file:
i=$(ls -t file.*.jpg | head -1 | awk -F. '{ print $2}') 
# if there weren't any matching files, force $i to 0
[ $i > 0 ] || i=0
# increment by one to get your starting value for $i
((i++))
# and then start your capture mechanism
while 1
do
  # increment our counter
  ((i++))
  # get the file and save it
  wget -O file.$i.jpg http://user:[email protected]/snapshot.cgi
  # presumably you want to wait some time after each retrieval
  sleep 30
done

    Really I should rewrite this whole thing as a perl one-liner but I'm tired and it's late so I'll be lazy. Anyway that should give you an idea of how to accomplish this with a simple shell script mechanism.

    • 3