Cat

lastmod 2026-02-06created 2015-10-2014 edits

The cat command can print the contents of a text file, or concatenate two or more files and print them.

Example

Print with a number on each line:

$ cat -b test.txt

Number blank lines too:

$ cat -n test.txt

Print two or more consecutive blank lines as a single line:

cat -s test.txt

Assign multi-line string

• stackoverflow - How does cat << EOF work in bash?

Examples of cat <<EOF syntax usage in Bash. For reference, this technique is called a Here document. See that page for details.

Assign multi-line string to a shell variable

$ sql=$(cat <<EOF
SELECT foo, bar FROM db
WHERE foo='baz'
EOF
)

The $sql variable now holds the new-line characters too. You can verify with echo -e "$sql"

Pass multi-line string to a file in Bash

$ cat <<EOF > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
EOF

The print.sh file now contains:

#!/bin/bash
echo $PWD
echo /home/user

Pass multi-line string to a pipe in Bash

$ cat <<EOF | grep 'b' | tee b.txt
foo
bar
baz
EOF

The b.txt file contains bar and baz lines. The same output is printed to stdout.

To prevent environment variable substitution

• Stackoverflow - How to avoid heredoc expanding variables?

Used as follows, $temp is substituted as an environment variable.

$ cat << EOF > tee b.txt
$temp
EOF

To prevent this, quote EOF with single quotes ('EOF').

$ cat << 'EOF' > tee b.txt
$temp
EOF

Text Processing Commands

See also

• socat
• split
• Tar#Splitting and joining files

Favorite site

• Linux cat, more, less, head, tail - viewing file contents