CODEWITHSUNDEEP
linuxwatch
Hack-R
Hack-R

Reputation: 23221

Use of watch to update image displayed in linux every N seconds fails

I have some codes that automatically generate Machine Learning plots on a server, sending plots to IoT clients at appropriate times for display.

The data pipeline works. However, my attempt to update the image in near real-time when a new plot is push is not working.

Currently my approach is:

user@client:~/data_viz $ watch -n3 feh -F plot0.png --zoom 200

where feh is some arbitrary lightweight Linux image viewer.

The problem is that even when the file (plot0.png) is overwritten successfully the viewer does not update until you kill it and restart it.

Update: I've acheived the world's worst version of this with the Bash approach below. The only problem now is that it flashes the desktop every second and will undoubtedly cause a seizure if I don't fix that...

$ watch -n2 sudo bash watch.sh

where watch.sh is 

#!/bin/bash
i="0"    
while [ $i -lt 4 ]
do
pkill feh
sleep 1
feh -F plot0.png --zoom 200&
sleep 1
pkill feh
done

There also seems to be no way to actually break the infinite loop even with Esc and ctrl+c. I want the loop to be infinite, but I also would prefer to be able to interrupt it when I have to.

Upvotes: 1

Views: 1051

Answers (1)

David C. Rankin
David C. Rankin

Reputation: 84609

While feh, like most image viewers/editors, does not watch the image-file for changes and automatically reload if changes occur, it does provide the -R, --reload <int> option that will cause feh to reload the image after the number of seconds specified as <int> transpire. For example:

feh --reload 5 image.png

will cause feh to reload image.png every 5 seconds. man 1 feh explains:

-R, --reload <int>

Reload filelist and current image after int seconds. Useful for viewing 
HTTP webcams or frequently changing directories. (Note that the filelist 
reloading is still experimental.)

If an image is removed, feh will either show the next one or quit. 
However, if an image still exists, but can no longer be loaded, feh 
will continue to try loading it.

Upvotes: 2

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