Are you new to “uniq”? Don’t worry! Let’s have a look at “uniq” and its usage.

What “uniq” is

Linux comes up with a big collection of tools and features. “uniq” is one of them. The tool works on the command line interface. The purpose of this tool is reporting and/or omitting repeated lines or strings of a file.

The tool just filters adjacent matching from INPUT (standard input) and write out to OUTPUT (standard output). If no option is specified, the tool will merge all the occurrences into the first occurrence.

Uniq usage

At first, let’s grab a text file to work with. For demo purpose, my “demo.txt” contains a number of duplicate entries.

• Omitting duplicates on a file

bat demo.txt

Note – Instead of “cat”, I’m using “bat” – a beautiful clone of “cat” with additional advanced features.

Now, open up the file with “uniq” –

uniq demo.txt

• Displaying the number of repetition

Using the “-c” flag, you can also ask “uniq” how many times a repeated line is repeated.

bat demo.txt

uniq -c demo.txt

• Printing the “duplicates” ONLY

Need to figure out the duplicates ONLY? Then use the “-d” flag with “uniq”.

bat demo.txt

uniq -d demo.txt

• Printing the “unique” ONLY

If you need to work with the unique lines ONLY, then you should use the “-u” flag.

bat demo.txt

uniq -u demo.txt

• Disable case sensitivity

When “uniq” is checking the strings, all the characters are case-sensitive, so, “Viktor” and “viktor” are different entry. Need to disable the case sensitivity? Then use the “-i” parameter.

bat demo.txt

uniq -i demo.txt

• Sorting and finding duplicates

In most of the cases, the duplicates may be scattered throughout the entire file. When you use “uniq” on that file, it can be misleading and confusing. So, what to do?

Well, sort out the file contents first and then, do the “uniq” thing!

bat demo.txt

sort demo.txt | uniq -c

• Ignoring characters

In cases, you may need to ignore the presence of a first few characters in the file. In that case, use the “-s” flag followed by the number of character you’d like to omit from the OUTPUT.

bat demo.txt

uniq -s 3 demo.txt

• Exporting the output to a file

It’s quite easy to export the output of any command into a file. Just check out this awesome tutorial on exporting command output to a file.

uniq -u demo.txt > demo-1.txt

bat demo-1.txt

Enjoy!

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“lsof” stands for “list open files”. Using this tool, you can identify what files are being used by which process/program. In the UNIX/Linux environment, every single thing is a file (pipes, directories, devices, sockets etc.). So, having a good knowledge of “lsof” can provide you with useful info in lots of scenarios.

Let’s check out some of the use cases of “lsof”.

“lsof” usage

The basic usage is listing all the open files that belong to all the active processes –

sudo lsof

The purpose of using “sudo” is to list ALL the files that are actively being used. Otherwise, it may not properly identify all the files.

You can also check if a specific file is being used.

sudo lsof <file_name>

Suppose, you need to identify what processes are accessing the file(s) of a certain directory.

lsof +D <directory_path>

lsof +d <directory_path>

Here, “+D” indicates to include the subdirectories within the directory. If you don’t want to include them, then use “+d”.

Need to find out the file(s) a certain process is accessing? Then use the “-c” flag. The command structure will be –

lsof -c <process_name> -c <process_name>

“lsof” is capable of handling multiple “-c” flags.

You can also list the processes that are using a certain mount point. For this purpose, the following structure must be followed –

lsof <mount_point>

Not all the processes in your system run under a certain user. For example, “root”, “<account_username>” etc. You can also tell “lsof” to show the files that are being used as a certain user permission.

lsof -u <username>

From the above example, need to exclude a certain user? Then you have to use “^” flag.

lsof -u ^<username>

It’s also possible to list all the files a certain process is accessing. Use the “-p” flag in this case. Note that as the value for the flag “-p”, you need to provide the PID of that process

lsof -p <PID>

List all the network connections –

lsof -i

Another interesting ability of “lsof” is listing all the processes that are listening to a specific port. For example, you want to find out what processes are using the 25 port.

lsof -i TCP:25

Need to scan a range of port, say, 1-25? Then the command structure will be the following one –

lsof -i TCP:1-25

You can also filter your result by IPv4 and IPv6.

# IPv4

lsof -i 4

# IPv6

lsof -i 6

Need to find out all the available options of “lsof”? You can get the help of the man page.

man lsof

You can also export the man page for future usage. Learn how to export Linux command output to a text file.

Enjoy!

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