sha224sum:tldr:8fdb7

This command uses a Linux shell syntax and consists of two parts separated by the | symbol, which is called a pipe.

The ${command} part is a placeholder representing an actual command that should be executed. It could be any executable command or a combination of commands enclosed within curly braces ${}. For example, if ${command} is replaced with the command ls, it would list the files and directories in the current directory.

The | symbol is called a pipe, and it allows the output of the preceding command (${command}) to be passed as input to the following command (sha224sum).

The sha224sum command is used to calculate the SHA-224 hash value of the input provided to it. It takes the input, performs a cryptographic hash function called SHA-224 on it, and produces a fixed-size output (224 bits or 28 bytes). This is often used for verifying the integrity of files or ensuring data integrity.

In summary, ${command} | sha224sum is a command sequence that first executes ${command} to generate some output (e.g., a file list), and then passes that output as input to the sha224sum command, which calculates the SHA-224 hash value of that input.