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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.
Example usage of tee: The output of ls -l is redirected to tee which copies them to the file file.txt and to the pager less. The name tee comes from this scheme - it looks like the capital letter T. The tee command is normally used to split the output of a program so that it can be both displayed and saved in a file. The command can be used to ...
read is a command found on Unix and Unix-like operating systems such as Linux. It reads a line of input from standard input or a file passed as an argument to its -u flag, and assigns it to a variable.
>> 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.
: duplicate an open file descriptor – System Interfaces Reference, The Single UNIX Specification, Version 4 from The Open Group; Redirection Definition by The Linux Information Project (LINFO) I/O Redirection in The Linux Documentation Project; Redirection in Windows; Creating a Child Process with Redirected Input and Output in Windows
The file is identified by a file descriptor that is normally obtained from a previous call to open. This system call reads in data in bytes, the number of which is specified by the caller, from the file and stores then into a buffer supplied by the calling process. The read system call takes three arguments: The file descriptor of the file.
On many systems it was necessary to obtain control of environment settings, access a local file table, determine the intended data set, and handle hardware correctly in the case of a punch card reader, magnetic tape drive, disk drive, line printer, card punch, or interactive terminal.
The other pseudo-device, the slave, emulates a hardware serial port device, [1] and is used by terminal-oriented programs such as shells (e.g. bash) as a processes to read/write data back from/to master endpoint. [1] PTYs are similar to bidirectional pipes. [3]: 1388 Devpts is a Linux kernel virtual file system containing pseudoterminal devices.