How To Text The File Using Linux Cat Command

 Overview

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Here we look at how to write text into a file using the Linux cat command.

The cat Command

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Cat command's common usages is to print the content of a file onto the standard output stream.

Other than that, the cat command allows us to write some texts into a file.

The Syntax

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Please look at the general syntax of the cat command:

cat [OPTION] [FILE]

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First, OPTION is a list of flags we can apply to modify the command’s printing behavior, 

whereas FILE is a list of files we want the command to read.

Making cat Read From stdin

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Let’s execute the cat command:

cat

Now try to enter some texts into the terminal:

cat

This is a appsolworld

This is a appsolworld

Once we are done, we can terminate the command by pressing CTRL+D.

[demantra@dsiddem demantra]$ cat >> a

appsolworld

^C

[demantra@dsiddem demantra]$ cat a

sfsfsfsd

appsolworld

[demantra@dsiddem demantra]$ cat > a

this

[demantra@dsiddem demantra]$ cat a

this

Writing to a File Using cat

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To write to a file, we’ll make cat command listen to the input stream and then redirect the output of 

cat command into a file using the Linux redirection operators “>”.

To verify our result, we can use the cat command once again:

cat readme.txt

This is a readme file.

This is a new line.

Appending Text to File Using cat!

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One thing we should note in the previous example is that it’ll always overwrite the file readme.txt.

If we want to append to an existing file, we can use the “>>” operator:

cat >> readme.txt

This is an appended line.

To verify that the last command has appended the file, we check the content of the file:

cat readme.txt

This is a readme file.

This is a new line.

This is an appended line.

The line we enter is appended to the end of the file instead of replacing the entire document.

Here Document

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It is also worth noting that the here document syntax can be used with the cat command:

cat > a.txt << EOF

This is an input stream literal

EOF

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EOF tells the cat command to terminate when it sees such a token in the subsequent lines.