yacas:tldr:7a46f

This command is using the Yacas computer algebra system to evaluate the expression "${Echo( Deriv(x)Cos(1-x) );}". Here's how it works:

1. The expression "${Echo( Deriv(x)Cos(1-x) );}" is enclosed in double quotes and passed as input through the echo command.
2. The echo command outputs the expression string to the standard output.
3. The pipe symbol (|) is used to redirect the standard output of the echo command as the input for the next command, which is yacas.
4. The yacas command starts the Yacas computer algebra system.
5. The "-p" option is used to enter the interactive input mode of Yacas, where the prompt is displayed for further input.
6. The "-c" option is used to execute the Yacas commands provided through the standard input.
7. "/dev/stdin" represents the file path for the standard input stream.
8. The expression "${Echo( Deriv(x)Cos(1-x) );}" is then read by Yacas from the standard input and evaluated.
9. The resulting output will be displayed in the terminal.

In summary, this command simply uses Yacas to compute the derivative of "Cos(1-x)" with respect to "x" and outputs the result.