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Bash Operators in Linux

Although Linux Distributions provide a Graphical User Interface just like any other operating system, the ability to control the system via the command line interface (CLI) has many benefits. A way to control how tasks are executed or how input and output is redirected, can be done using operators.

Although Linux Distributions provide a Graphical User Interface just like any other operating system, the ability to control the system via the command line interface (CLI) has many benefits. A way to control how tasks are executed or how input and output is redirected, can be done using operators.

1) Command “chaining”

  • Sequence: ;

Executing multiples tasks, one after another. After the first task is completed, the next task will execute. After the second is completed, the third will execute and so on:

Bash Operators in Linux

  • Parallel execution: &
Execute tasks at the same time.

Command chaining


2) Conditional execution:

  • And operator: &&
Task 2 will be executed only if Task 1 was successful

Bash Operators Conditional Execution

  • Or operator: ||
Task 2 will be executed only if Task 1 was unsuccessful

Bash Operators Conditional Execution Task


3) Pipelines: |, |&

  • Pipe operator: |
Used to send output from Task 1 (stdout) to input of Task 2 (stdin)

Bash Operators Pipelines

  • Pipe error operator: |&

Error output of Task1 (stderr) is also redirected to input of Task 2 (stdin)

Bash Operators in Linux Pipelines 

4) Input / output redirection

  • Redirecting input: < 

Used for command that read their input from the terminal. Input is read from from file, instead of terminal

Syntax: command < file

Bash Operators Input / Output Redirection

  • Redirecting input – here documents: <<

Used when the input of a command should be taken directly from the terminal, rather that from a file

Bash Operators Linux Input / Output Redirection

  • Redirecting input – here string:  <<<
Used when a single string should be redirected to the input of the command

Bash Operators Redirecting Input

  • Redirecting output – stdout: >, >>

Used for commands that write output to the terminal.

Syntax: 

command > file – write output to file. If file doesn’t exist, it is created. If it exists, it will be truncated

command >> file – write output to file. If file doesn’t exists, it is created. If it exists, output will be appended

Note: Stderr is still written to the terminal

Bash Operators Syntax

  • Redirecting output – stderr: 2>, 2>>

Sends stderr to file.

Syntax: 

command 2> file – write stderr to file. . If file doesn’t exist, it is created. If it exists, it will be truncated

command 2>> file – write stderr to file. If file doesn’t exist, it is created. If it exists, output will be appended

Note: Output (stdout) is still written to the terminal

Bash Operators in Linux Syntax

  • Redirecting output – stdout and stderr: &>, &>>

Used to redirect both stdout and stderr for the same command

Syntax: 

command &> file – send stdout and stderr to file. If file doesn’t exist, it is created. If it exists, it will be truncated

command &>> file – send stdout and stderr to file. If file doesn’t exist, it is created. If it exists, output will be appended

Bash Operators command file

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Florin Simion
Linux Expert


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