Bash, the Bourne Again Shell, is a powerful tool for Unix-based systems. It offers a wide range of functionalities, including the ability to redirect input and output between commands and files. This article will delve into the specifics of three key redirection operators in bash: <<, <<<, and < <. These operators, while similar in appearance, have distinct uses and functionalities.
The <<, <<<, and < < redirection operators in bash have distinct uses and functionalities. The << operator, also known as a Here Document, is used for multi-line input. The <<< operator, or Here String, is used for single-line strings. The < < operator combines input redirection and process substitution to redirect the output of one command as input to another command. Each operator has its own strengths and understanding their uses can enhance your bash scripting skills.
The << Operator: Here Document
The << operator, also known as a Here Document, is used to redirect input into a command or script. It allows you to specify a delimiter that marks the end of the input. The input is then provided directly within the script or command, usually followed by the specified delimiter.
Here’s an example of how it works:
wc << EOF
Hello
World
EOFIn this example, wc is a command that counts lines, words, and characters. The << EOF part tells the shell that we’re starting a Here Document, and EOF (End Of File) is the chosen delimiter. The lines that follow up to the EOF are the input to the wc command.
The <<< Operator: Here String
The <<< operator, or Here String, is used to provide a pre-made string as input to a command. Unlike the << operator, which allows for multiple lines of input, the <<< operator passes a single string directly to the command without the need for additional input or a delimiter.
Here’s an example:
bc <<< 5*4In this case, bc is a calculator command, and 5*4 is the string that we’re passing as input. The <<< operator tells the shell to treat the following string as input to the bc command.
The < < Operator: Input Redirection with Process Substitution
The < < operator is a combination of input redirection (<) and process substitution (<()). It’s important to note that < < is not a standalone operator.
Process substitution allows the output of a command to be treated as a file. Input redirection, on the other hand, redirects the contents of a file to a command’s input. By combining these two functionalities, the < < operator allows you to redirect the output of one command as input to another command.
Here’s an example:
command1 < <(command2)In this example, command2 is executed first. Its output is treated as a file, which is then redirected as input to command1.
Conclusion
In the battle of bash redirection operators, <<, <<<, and < < each have their own strengths. The << operator is perfect for multi-line input, the <<< operator is great for single-line strings, and the < < operator excels at redirecting output from one command to another. Understanding these operators and their uses can significantly enhance your bash scripting skills.
For more information on bash scripting and redirection operators, check out the GNU Bash Manual.
The << operator, also known as a Here Document, is used to redirect input into a command or script. It allows you to specify a delimiter that marks the end of the input. The input is then provided directly within the script or command, usually followed by the specified delimiter.
The <<< operator, or Here String, is used to provide a pre-made string as input to a command. Unlike the << operator, which allows for multiple lines of input, the <<< operator passes a single string directly to the command without the need for additional input or a delimiter.
The < < operator is a combination of input redirection (<) and process substitution (<()). It allows you to redirect the output of one command as input to another command. It’s important to note that < < is not a standalone operator.
Certainly! Here’s an example:
wc << EOF
Hello
World
EOFIn this example, wc is a command that counts lines, words, and characters. The << EOF part tells the shell that we’re starting a Here Document, and EOF (End Of File) is the chosen delimiter. The lines that follow up to the EOF are the input to the wc command.
The <<< operator is used to pass a pre-made string as input to a command. Here’s an example:
bc <<< 5*4In this case, bc is a calculator command, and 5*4 is the string that we’re passing as input. The <<< operator tells the shell to treat the following string as input to the bc command.
