tcsh:tldr:c0e93

This command involves the use of pipes and the command tcsh, which is a Unix shell (specifically, the Tenex C shell).

${echo "echo 'tcsh is executed'"} is a variable expansion that substitutes the value of the variable with its contents. In this case, the variable contains the command echo 'tcsh is executed', which prints the given statement when executed.

The pipe character | connects the standard output of one command (in this case, the expanded variable) to the standard input of another command (tcsh). It allows the output of one command to be used as the input of another.

Finally, tcsh is a shell command that runs the Tenex C shell, which is an interactive shell and scripting language. It executes the commands received through the pipe.

Overall, this command expands the variable to generate the statement echo 'tcsh is executed', and then uses a pipe to send that statement as input to the tcsh shell, causing it to be executed.