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By itself, the yes command outputs 'y' or whatever is specified as an argument, followed by a newline repeatedly until stopped by the user or otherwise killed; when piped into a command, it will continue until the pipe breaks (i.e., the program completes its execution).
This runs the ftp client with input user, press return, then pass. In casual use, the initial step of a pipeline is often cat or echo, reading from a file or string. This can often be replaced by input indirection or a here string, and use of cat and piping rather than input redirection is known as useless use of cat. For example, the following ...
Each process takes input from the previous process and produces output for the next process via standard streams. Each | tells the shell to connect the standard output of the command on the left to the standard input of the command on the right by an inter-process communication mechanism called an (anonymous) pipe, implemented in the operating ...
xargs (short for "extended arguments") [1] is a command on Unix and most Unix-like operating systems used to build and execute commands from standard input. It converts input from standard input into arguments to a command. Some commands such as grep and awk can take input either as
Most operating system shells are not direct interfaces to the underlying kernel, even if a shell communicates with the user via peripheral devices attached to the computer directly. Shells are actually special applications that use the kernel API in just the same way as it is used by other application programs.
The above script records to script.log all output of the exec command. However, some interactive programs (such as Python) do not echo their standard input when run under the resulting shell, although they do when run under the script command, again due to the detection of a terminal.
The tty command is commonly used to check if the output medium is a terminal. The command prints the file name of the terminal connected to standard input. If no file is detected (in case, it's being run as part of a script or the command is being piped) "not a tty" is printed to stdout and the command exits with an exit status of 1.
Standard input is a stream from which a program reads its input data. The program requests data transfers by use of the read operation. Not all programs require stream input. For example, the dir and ls programs (which display file names contained in a directory) may take command-line arguments, but perform their operations without any stream ...