ect:tldr:50172
ect: Compress a file.
$ ect ${filename-png}
try on your machine
The command you provided, "ect ${filename-png}", assumes that $filename is a variable containing the name of a file without the file extension.
In this case, the command intends to convert the given file into the PNG image format. The "${filename-png}" part is a parameter expansion syntax, where it appends "-png" to the value of the $filename variable.
For example, if $filename is "image", then "${filename-png}" will be "image-png". The resulting command would be something like "ect image-png", instructing the "ect" command to convert the "image" file to the "image-png.png" format.
This explanation was created by an AI. In most cases those are correct. But please always be careful and
never run a command you are not sure if it is safe.