vale:tldr:89b99

This command is used to pipe the contents of a file (specified by the variable ${file-md}) to the Vale command-line tool. Here's how it works:

1. ${file-md} is a variable that represents the name of the file, with ".md" as the file extension. The actual value of ${file-md} should be provided before running this command.

2. cat is a command in Unix-like operating systems that concatenates and displays the contents of files. In this case, it is used to read the contents of the specified file.

3. The | symbol is a pipe operator, which takes the output of the previous command (cat in this case) and passes it as input to the next command (vale).

4. vale --ext=.md is the Vale command-line tool. It is a linter that analyzes and provides feedback on the content of Markdown files. --ext=.md specifies that it should only evaluate files with the ".md" extension.

So, when this command is executed, it reads the contents of the specified file using cat, then pipes it to vale for analysis with the specified extension filter. The Vale tool will then process the content and provide feedback or warnings based on the linter's rules and configurations.