Using cat in Bash to Show Contents of a File

You can use echo to show lots of lines in bash. But cat is simpler and easier to read.

How to do it

When we want to show multiple lines, we can use cat to read the lines into the script and display them.

We start with a starter cat<<end_word and we can put lines in until we begin a line with the end_word. Usually the end_word is EOF, but it can be any word, Thatisit or HELLO.

cat<<end_word
We can put whatever we want
    here
   and
  bash
 will 
  show
   it
    exactly
end_word

The above means “read the input until the end_word is reached.”

Thus if we cant to show a lot of lines in a shell script we can use cat and then read them in:

cat<<EOF
Just some things to say
on a few lines
without lots of echos
EOF

And that will show:

Just some things to say
on a few lines
without lots of echos

Escaping Variables

If we put $ in the input, it will be treated as a variable. So we just have to comment it out:

x=3
cat<<EOF
We want to know what x is:
 \$x = $x
EOF

This outputs:

We want to know what x is:
 $x = 3

This can be really nice if we need to output a lot of variables:

x=1
cat << EOF
Show $x
Then 2
Then $(($x + 2)
EOF

Will print:

Show 1
Then 2
Then 3

And if you don’t want cat<< to do variable substitution:

cat << 'EOF'
Print $this as is
EOF

Output to a file

To output to a file (note that a single > overwrites the file):

total=12
cat << EOF > /path/to/file
The total is $total
EOF

The file will contain:

The total is 12

And to just add to the file use >>

total=24
cat << EOF >> /path/to/file
The total is $total
EOF

The file will now contain:

The total is 12
The total is 24