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The reason for this is to distinguish between a file named '1' and stdout, i.e. cat file 2 >1 vs cat file 2 > & 1. In the first case, stderr is redirected to a file named ' 1 ' and in the second, stderr is redirected to stdout. Another useful capability is to redirect one standard file handle to another.
In the case of an interactive shell, that is usually the text terminal which initiated the program. The file descriptor for standard output is 1 (one); the POSIX <unistd.h> definition is STDOUT_FILENO; the corresponding C <stdio.h> variable is FILE* stdout; similarly, the C++ <iostream> variable is std::cout.
Similarly, both the stdout and stderr output streams can be redirected to standard output and the program.lint using stream redirection: lint program.c 2 > & 1 | tee program.lint To view and append the output from a command to an existing file:
Yes (stdin, stdout, stderr, stdout+stderr) Yes (via registry, TCMD.INI / 4NT.INI file, startup parameters, environment variables, SETDOS command) Yes (automatic via registry and TCSTART / 4START as well as TCEXIT / 4EXIT, or explicitly via /K startup option) Yes (via CALL command or /C and /K startup options) Yes No VMS DCL [22] OpenVMS
Under Unix, devices are files too, so the normal type of file for the shell used for stdin, stdout and stderr is a tty device file. Another command-line interface allows a shell program to launch helper programs, either to launch documents or start a program.
Note that these methods prevent the process from being sent a 'stop' signal on logout, but if input/output is being received for these standard I/O files (stdin, stdout, or stderr), they will still hang the terminal. [1] See Overcoming hanging, below. nohup is often used in combination with the nice command to run processes on a lower priority.
JShell is a Java read-eval-print loop which was first introduced in the JDK 9. [1] It is tracked by JEP 222 jshell: The Java Shell (Read-Eval-Print Loop). [2] One reason why JShell was proposed for Java 9 is the lack of a standard interactive environment for the language; the de facto library to use a Java REPL was often BeanShell, which has been dormant since 2003, and arbitrarily diverged ...
The command ls -l is executed as a process, the output (stdout) of which is piped to the input (stdin) of the process for grep key; and likewise for the process for less. Each process takes input from the previous process and produces output for the next process via standard streams .