entr:tldr:4af82

This command consists of two parts separated by the pipe symbol (|).

1. ${ls *-rb}

   • ls *-rb: This command lists the files in the current directory that have filenames ending with -rb. The * is a wildcard character that matches any characters before the -rb suffix.
   • ${}: The command is enclosed in ${} which typically means it is meant to be expanded into a variable or command substitution.

2. entr -r ${ruby main-rb}

   • entr: This is a command-line tool that monitors files and directories for changes and executes a given command whenever any changes occur.
   • -r: This flag tells entr to monitor the listed files or directories recursively.
   • ${ruby main-rb}: This is a placeholder meant to be replaced with the command ruby main-rb. It suggests that the command ruby main-rb should be executed whenever changes are detected by entr.

Overall, the command lists the files with names ending in -rb and passes the list of filenames into entr to monitor for changes. Whenever a change is detected in any of the files, the command ruby main-rb will be executed.