Linux Command - cat

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cat - print and concatenate files.

Syntax

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cat [OPTION] [FILE]...

Description

Concatenate FILE(s), or standard input, to standard output.

Option Description
-n –number Number all output lines including blank lines

Example

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cat file1
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cat -n file1

concatenate files into a single file

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cat file1 file2 > file3

concatenate files and append to file3

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cat file1 file2 > file3

clean up the contents in file1

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cat /dev/null > file1

Pass a multi-line string to a file

You can sometimes see cat command use together with heredoc

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cat <<EOF > print.sh
#!/bin/bash
echo "Hello World"
EOF

concatenate and print files in reverse order

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tac file1

tac is the reverse of cat.

Reference