How to Cat EOF in Bash
This tutorial explains what cat EOF is and its usage in bash.
Cat EOF in Bash
cat is a bash command used to read, display, or concatenate the contents of a file, while EOF stands for End Of File. The EOF is an indication to the shell that the file that was being read has ended. cat << eof uses here-document. The redirection operators << and <<- both allow redirection of subsequent lines read by the shell to the input of a command. The redirected lines are called here-document.
The here-document uses the following format.
[n] << word
here-document
delimeter
The here-document is treated as a single word that begins after the next newline. It continues until there is a line containing only the delimiter or a new line with no blank characters in between.
Put a Multi-line String to a File in Bash
cat, <<, EOF, and > provide an interactive way to input a multi-line string into a file. The EOF is known as the Here Tag. The Here Tag tells the shell that you will input a multi-line string until the Here Tag. The << is used to set the Here Tag. The > is used to redirect the input content to a specified file, multiline.txt in our case.
cat << EOF > multiline.txt
> This is the first line
> This is the second line
> This is the third line
> EOF
We can also use cat, <<, EOF, and > to write bash scripts as shown below interactively.
cat << EOF > script.sh
#!/bin/bash
printf "Hello\n"
printf "Wordl!\n"
EOF
Pass Multi-line String to Pipe in Bash
The code below uses cat, eof, and pipe to redirect multi-line input string content to a specified pipe and command. The input is piped to the grep command which greps for string A and the matched input is piped to the tee command. The tee command copies the input to the fruits.txt file.
cat <<EOF | grep 'A' | tee fruits.txt
> Apple
> Orange
> Apricot
> Banana
> EOF
Let’s check the content of the fruits.txt file with cat.
cat fruits.txt
Output:
Apple
Apricot
