fish:tldr:10281

The fish --command command is used to execute the given command string as if it were entered directly into the fish shell.

In this specific case, the command is fish --command "${echo 'fish is executed'}". Here is a breakdown of what it does:

1. fish: It invokes the fish shell.
2. --command: It specifies that a command string should be executed.
3. "${echo 'fish is executed'}": This is the command string being executed.

Within the command string:

• ${...} is a way to execute a command inside a string. Here, the command ${echo 'fish is executed'} is executed.
• echo 'fish is executed' is a simple command to output the string fish is executed.

So when you run fish --command "${echo 'fish is executed'}", it will launch the fish shell and execute the command echo 'fish is executed', resulting in the output fish is executed being displayed in the shell.