Difference between ant and ant clean all?

"ant" runs the default target of the project.

"ant clean all" runs the clean target with parameter all.

The exact function depends on your definition of those targets. Generally speaking people use clean to clean up and have a fresh start, and default to rebuild the project, but again all depend on the way those targets are defined in the build file.

NOTE: "ant all" and "ant clean all" is related to generating the Model classes and .class files.
1)ant :- is a build framework tool provided by Apache.

2)ant clean all :- * it checks the hybris folder structure (i.e,. bin,config,log folders), is installed or not (if not , it will install it). * if any changes (such as creating a new itemType in *-items.xml , or modifing itemType by adding the new attributes) then "ant clean all" will delete the class and again re-create it. (hence, consume more time compared to ant all)

3)ant all :- * it doesnt checks the hybris folder structure (i.e,. it assumes bin,config,log folders are already present in hybris directory). * if any changes (such as creating a new itemType in *-items.xml , or modifing itemType by adding the new attributes) then "ant all" will modify it (i.e,. instead of deleting and recreating, it will only modify the required changes (such as if you add onlineDays attribute is PRODUCT itemType) in the existing class itself). (hence, consume less time compared to ant clean all).