Renaming images in specific sequence

All, I'm new to the software and in the initial stages of learning curve. I have bunch of images that I want to rename in following way -

Original name Updated name
<something_random>.jpg G1_001_front
<something_random>.jpg G1_001_back
<something_random>.jpg G1_002_front
<something_random>.jpg G1_002_back
<something_random>.jpg G1_003_front
<something_random>.jpg G1_003_back

In general naming pattern will be
G1_xxx_yy; where yy will have 2 values, "front" and "back" and xxx will start from 001 and end at 999. All images are already arranged in chronological order.

I'm not able to find a function that will allow me to do this. Any help is appreciated!

Thanks
Shan

Assuming the filenames are already in the correct order in the list, this script will do it:

num = Math.ceil((index + 1) / 2 );
side = (index % 2) ? '_back' : '_front';
return 'G1_' + ("00"+num).slice(-3) + side;


"index" is the position of the filename in the list - starting from zero at the top.

The function Math.ceil(x) rounds x UP to the nearest integer.

"%" is the modulo operator and returns the remainder after division, so "index % 2" will be zero if index is odd and 1 if it is even.

"?" is the conditional operator - syntax: (condition) ? value_if_true : value_if_false


For help on JavaScript Google is your friend - you will probably find hits at www.w3schools.com are usually most helpful.

Reply to #2:
Thank you for the elaborate response and providing working solution! I will go through the reference you have pointed out.

Best,
Shantanu