grim:tldr:236bb

The given command is using the grim tool to capture a screenshot and save it as a PNG file with a specified filename.

Here's a breakdown of the command:

• grim: This is the command for the grim tool, which is a screenshot utility in the Wayland display server.
• "${filename-png}": This is a parameter passed to the grim command enclosed within double quotes. The parameter specifies the filename for the screenshot and uses a shell parameter expansion technique called "parameter substitution."
  • ${filename-png}: This is the parameter ${filename} with the suffix -png appended to it. The -png suffix indicates the desired file format as PNG. ${filename} refers to a variable, likely containing the name of the desired screenshot file.
  • The parameter substitution essentially replaces ${filename} with the value it holds and adds the -png suffix, thus producing the filename with the PNG extension.

To summarize, the command captures a screenshot using grim and saves it as a PNG file with a filename provided by the ${filename} variable.