Scripting

3.7    Standard Input and Standard Output

In Bash, there are three “channels” that use commands for input and output:

• Standard output (stdout)Results of a command are directed to the what’s called the “standard output.” When you run ls, the result of this command is the list of all files in the local directory. This result is output as text and is typically displayed in the terminal.

• Error messages (standard error = stderr)Usually, error messages are also displayed in the terminal. Internally, however, error messages are routed to a different channel, resulting in the possibility of treating normal output and error messages differently.

• Standard input (stdin)Many commonly used variables process text files whose name is passed as a parameter. ...