Standard I/O & Error Redirection

Standard I/O & Error RedirectionThe 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.

Save time and money by making the right web hosting decision the first time.

WordPress.com

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Data-Driven Reviews

  • Current & accurate reviews are based on data and supported by real user experiences.
  • The goal is to deliver the most accurate information possible based on the needs of the majority of website owners and developers, and Ananova reports deliver the most reliable indicators of web host performance.

Save time and money by making the right web hosting decision the first time.

WordPress.com

Nexcess Hosting

Visit nexcess

Inmotion Hosting

Visit Inmotionhosting

Namecheap Hosting

Visit Namecheap

iThemes Hosting

Visit ithemes

Data-Driven Reviews

  • Current & accurate reviews are based on data and supported by real user experiences.
  • The goal is to deliver the most accurate information possible based on the needs of the majority of website owners and developers, and Ananova reports deliver the most reliable indicators of web host performance.
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