Understanding the `cat` Command in Linux
The cat
(short for "concatenate") command is one of the most frequently used
commands in Linux. It reads data from files, and outputs their contents. It is
commonly used for displaying the content of files, combining copies of different
files and creating new ones.
Syntax
The basic syntax of the cat
command is as follows:
cat [OPTION]... [FILE]...
Here, [OPTION]
is used to specify the behavior of the cat
command
and [FILE]
is the name of one or more files you want to read. If no file is
specified, or if the -
is used as one of the input files, cat
will read from
the standard input.
Options
Below is a table of common options for cat
:
Option | Shorthand | Description |
---|---|---|
--number-nonblank | -b | Number non-empty output lines, overrides -n |
--number | -n | Number all output lines |
--squeeze-blank | -s | Squeeze multiple adjacent blank lines |
--show-ends | -E | Display $ at the end of each line |
--show-tabs | -T | Display TAB characters as ^I |
--show-nonprinting | -v | Use ^ and M- notation, except for LFD and TAB |
Examples
Example 1: Displaying Content of a File
To display the content of a file named example.txt
, you would use:
cat example.txt
Example 2: Creating a File with cat
To create a file, you can redirect the output of cat
to a file:
cat > newfile.txt
After running the command, type your desired content and then press CTRL+D
to
save it.
Markdown of newfile.txt
:
Hello, this is a text file.
This is the second line.
Example 3: Combining Files
To combine the contents of file1.txt
and file2.txt
into combined.txt
:
cat file1.txt file2.txt > combined.txt
To create file1.txt
and file2.txt
for this example:
echo -e "First file's content." > file1.txt
echo -e "Second file's content." > file2.txt
Example 4: Using Options with cat
To number all lines of a file:
cat -n example.txt
If you want to squeeze multiple blank lines into a single blank line:
cat -s example.txt
Example 5: Viewing Non-Printable Characters
To see tabs and end-of-line markers in a file:
cat -ET example.txt
Combining cat
with Other Commands
The cat
command can also be used in conjunction with other Linux commands
through pipes (|
). For example, to paginate the contents of a file, you can
use cat
with less
:
cat example.txt | less
Or to count the number of lines in a file:
cat example.txt | wc -l
By understanding and using the cat
command, Linux users can perform a wide
array of file manipulation tasks quickly and efficiently. Whether you are
concatenating files, viewing content, or piping data into other commands, cat
is an indispensable tool in command-line operations.
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