# mmv > Move and rename files in bulk. > More information: . - Rename all files with a certain extension to a different extension: `mmv "*{{.old_extension}}" "#1{{.new_extension}}"` - Copy `report6part4.txt` to `./french/rapport6partie4.txt` along with all similarly named files: `mmv -c "{{report*part*.txt}}" "{{./french/rapport#1partie#2.txt}}"` - Append all `.txt` files into one file: `mmv -a "{{*.txt}}" "{{all.txt}}"` - Convert dates in filenames from "M-D-Y" format to "D-M-Y" format: `mmv "{{[0-1][0-9]-[0-3][0-9]-[0-9][0-9][0-9][0-9].txt}}" "{{#3#4-#1#2-#5#6#7#8.txt}}"`