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cat > outfile.txt <<EOF
>some text
>to save
>EOF

cat is one of the most frequently used commands on Unix-like operating systems. It has three related functions with regard to text files:

1. displaying them
2. combining copies of them
3. creating new ones.
4. Copy files

cat's general syntax is:

cat [options] [filenames] [-] [filenames]

Reading Files

The most common use of cat is to read the contents of files, and cat is often the most convenient program for this purpose. All that is necessary to open a text file for viewing on the display monitor is to type the word cat followed by a space and the name of the file and then press the ENTER key. For example, the following will display the contents of a file named file1:

cat file1

Concatenation

The second role of cat is concatenation. (This is the source of cat's curious name.) There is no effect on the original files.

For example, the following command will concatenate copies of the contents of the three files file1, file2 and file3:

cat file1 file2 file3

The contents of each file will be displayed on the monitor screen. This output could just as easily be redirected using the output redirection operator to another file, such as file4, using the following:

cat file1 file2 file3 > file4

File Creation

Thanks to @muru comment : cat is capable of create new files depending on the shell redirection feature and not itself

For small files this is often easier than using vi, gedit or other text editors. It is accomplished by typing cat followed by the output redirection operator and the name of the file to be created, then pressing ENTER and finally simultaneously pressing the Ctrl & d keys.

For example, a new file named file1 can be created by typing

cat > file1

then press ENTER and simultaneously press the Ctrl & d keys.

PS1: If a file named file1 already exists, it will be overwritten

PS2: you can append to exited file using append operator >> example cat >> file1

Copy Files

The cat command can also be used (depending on shell redirection feature) to create a new file and transfer to it the data from an existing file. Example: make a copy of file oldfile.txt:

cat oldfile.txt > newfile.txt

References:

• Linux and Unix cat command
• The cat Command
• cat (Unix)
• HowTo: Use cat Command In Linux / UNIX

A few words about.

As far as I can tell from a quick glance at the source code, cat uses a buffer to optimize its workflow. Referring to the behavior of the simple cat invocation, from standard input and without special command line options:

1. when the buffer is empty a single Ctrl+D it is enough to exit;
2. when not, the first Ctrl-D forces the buffer dump (which becomes empty), and the second is interpreted as the command to quit.

This means that if you run your cat> test and simply enter Ctrl-D you will create an empty file (named test) in the current directory, or you will empty the file if it already exists, without the need for a second Ctrl-D .

Beyond the scope of this question, but not so remote: it should be noted that if you are sending characters to a terminal/shell instance an unnecessary second Ctrl-D could cause an unwanted exit (mainly connected to the example above).