The numbers 0, 1, and 2 refer to the standard input, standard output, and standard error, respectively.
I/O Redirection
- > Redirect the standard output to a file or device, it creates the file, if it does not exists and overwrites if does exists
- >! Forces the overwriting of a file, if already exists, thus overriding noclubber option.
- >> Appending the output to the end of the file. It can be used to unify multiple files
cat file1 file2 file3> new-file
- < Redirect the standard input from a file or device to a program or command
Error Redirection
When a command fails to execute, the system issues an error message which gets displayed on a screen by default. To keep the record of the error messages, they are redirected to a file using special redirection operators.
- 2> Redirect the standard error to a file or device
- 2>> Redirect and append the standard error to a standard output
- 2>&1 Redirect the standard error to standard output
- >& Redirect the standard error to a file or device
Pipes
- Command | Command Pipe the standard output of one command as input for another command
- Command | &Command Pipe the standard error as input to another command in the C-shell
The Pipe | operator placed between two commands forms a connection between them. They make the CLI incredibly powerful, efficient and versatile. It creates a unidirectional data channel used for interprocess communication.
- Using pipe with less
dig ananova.com | less - Count the number of lines of output after command execution
grep “Linux Hosting” *.php | wc -l - With sort
du -khs * | sort -h
Named Pipe
mkfifo <pipe-name> mknod p <pipe-name>
Its special file, which follows FIFO (First-in, First-out character) mechanism used even over multiple shell sessions. The size of the named pipe is zero and has a designation of “p.” They resided in memory rather than being written to disk.
$ mkfifo hosting $ ls -l hosting
64-bit computer architecture and availability of large memory computer systems enables the distribution of application among multiple processes, which communicate with each other using IPC (Interprocess communication). In a networking environment, these processes run on different systems.
