| (Pipe operator) - DOS/Command Prompt Reference
Treats the output of the command written in the left side of ‘|’ symbol as the input of the command written in the right side.
<command1> | <command2>
Pipe performs connecting the output of the left-side command to the input of the right-side command. By using pipe, connecting the output of a command to the input of another one can be written as one-liner. No need to use temporary file for data transfers between commands.
[MS-DOS only] To use pipe, ‘TEMP’ environment variable must be set.
[Windows NT series] [Extensions] When calling labels in batch files by using Call, you cannot transfer Call's output with pipe. (You can write its output to the file by using output redirect.)
type C:\config.sys | more
Outputs C:\config.sys by using Type command, but the content is output per screen by More command.
echo Y| del "%TEMP%\*.*"
Deletes files (not directories) in TEMP directory by using Del command. Del command with specifying such as "*.*" always prompts whether to delete, so you can send Y by using Echo and ‘|’, which will be the response of Del's prompt.