Since G'mic loads files in memory before processing them, if you have a large number of files to process, you may not have enough memory to do it. In that case, the trick is to load an image, process it and remove it from memory before loading the next one. Here is how you can do it.
Let's say you have two directories called 'original' and 'processed'. The first contains JPEG files, that you want to turn gray and put in the second one.
The bash script below creates a grey version of all the files finishing with .jpg in the directory called 'original' and output them in the directory called 'processed':
cd original for i in *jpg do gmic $i -to_gray -o ../processed/$i done
The bash script below uses the thrid row to read custom command from a file named CommandFile. Custom command -custom_command specifed by the command file is applied to all tif files in current directory. Files are outputted with prefix tmp_. Fourth row reads intermediary tmp_ ouputs and saves the files in data type ushort as 16 bit tiff images with prefix Processed_. Fifth row removes intermediary tmp_ files.
for i in *tif do gmic -m [CommandFile] $i -[custom_command] -outputp tmp_ gmic tmp_$i -o Processed_$i,ushort rm ./tmp_$i done
for this to work the shell script should be run from working directory and working directory should contain both the custom command file, shell script and tiff tiles to process.
It exists a G'mic command that does it too, but it is a bit tricky.
The script below goes into the directory called 'processed', then, the G'mic command turns to gray the files finishing with .jpg in the directory called 'original' and output them in the current directory, adding the prefix 'gray_' to the name:
cd processed gmic -apply_files \"-to_gray\",\" ../original/*.jpg \",gray_
There are two things to care about:
1. you should put \" before and after the command to execute, especially if it contains spaces;
2. you should put \" before and after the file list but also a space after the first \" and before the second \". And filenames can't contain spaces.
The batch file below creates a grey version of all the files finishing with .jpg in the current directory and outputs them in the sub-directory called 'processed':
MD processed FOR %%a in (*.jpg) DO gmic -i %%a -to_gray -o processed\%%a PAUSE
If you want to also load the latest gmic update file you will need to make sure it's either in the same directory as you're running the batch file from or put the full path to it in the command. For example:
MD processed FOR %%a in (*.jpg) DO gmic -m c:\gmic\update1585.gmic -i %%a -to_gray -o processed\%%a PAUSE