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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.
The C programming language provides many standard library functions for file input and output.These functions make up the bulk of the C standard library header <stdio.h>. [1] The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, [2] and officially became part of the Unix operating system in Version 7.
>> file means stdout will be appended at the end of file. >>& file means both stdout and stderr will be appended at the end of file. < file means stdin will be read from file. << string is a here document. Stdin will read the following lines up to the one that matches string. Redirecting stderr alone isn't possible without the aid of a sub-shell.
Text files can serve either purpose as well. This provides the interfaces of piping, filters and redirection. 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.
KornShell (ksh) is a Unix shell which was developed by David Korn at Bell Labs in the early 1980s and announced at USENIX on July 14, 1983. [1] [2] The initial development was based on Bourne shell source code. [7]
GUIs created with scripting tools like Zenity and KDialog by KDE project [9] make use of stdin, stdout, and stderr, and are based on simple scripts rather than a complete GUI programmed and compiled in C/C++ using Qt, GTK, or other equivalent proprietary widget framework.
All shells related to Bourne shell (sh), for example Thompson shell (sh), Bash (bash), KornShell (ksh), and Z shell (zsh), allow the stdout and stderr to be attached to a named pipe and redirected to the tee command, for example:
File descriptors for a single process, file table and inode table. Note that multiple file descriptors can refer to the same file table entry (e.g., as a result of the dup system call [3]: 104 ) and that multiple file table entries can in turn refer to the same inode (if it has been opened multiple times; the table is still simplified because it represents inodes by file names, even though an ...