coproc:tldr:d3ee2

This command sets up a coprocess, which is a form of process substitution in the shell. A coprocess allows you to communicate with a command as if it were a file.

Here is a breakdown of the command:

1. coproc BC { bc --mathlib; }:

   • coproc is the keyword used to establish a coprocess.
   • BC is the name of the coprocess, which is used as an array variable to refer to the input/output file descriptors of the coprocess.
   • { bc --mathlib; } is the command that the coprocess runs. In this case, it launches the bc command with the --mathlib option, which loads the math library for advanced mathematical calculations.

2. echo "1/3" >&"${BC[1]}":

   • echo "1/3" outputs the string "1/3".
   • >&"${BC[1]}" redirects the output of the echo command to the coprocess's input file descriptor. ${BC[1]} is the second element (index 1) of the BC coprocess array, which refers to the output file descriptor of the coprocess.

3. read output <&"${BC[0]}":

   • read output reads input from the coprocess's output file descriptor and stores it in the variable output.
   • <&"${BC[0]}" redirects the coprocess's output file descriptor to the input of the read command. ${BC[0]} is the first element (index 0) of the BC coprocess array, which refers to the input file descriptor of the coprocess.

4. echo "$output":

   • echo "$output" outputs the value stored in the output variable, which is the result of the previous calculation performed by the coprocess.

To summarize, the command establishes a coprocess running the bc command with the math library enabled. It then sends the string "1/3" to the coprocess for calculation, reads the output from the coprocess, and finally, prints the result. In this case, the result should be "0.33333333333333333333" (the decimal representation of 1/3 according to bc's math library).