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John Au-Yeung
John Au-Yeung

Posted on • Originally published at thewebdev.info

Useful Linux Commands — Users, Groups, and Remote Connections

#webdev #programming #productivity #linux

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Linux is an operating system that many developers will use.

Therefore, it’s a good idea to learn some Linux commands.

In this article, we’ll look at some useful Linux commands we should know.

printf

printf is an improved version of the echo command.

It lets us format and adds escape sequences:

printf "1\n3\n2"
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We can also use it with < to get input from it and sort it with sort :

sort <(printf "1\n3\n2")
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0 / 1 / 2

0, 1, and 2 are the standard input, output, and error streams, respectively.

For instance, we can redirect to stdout with:

echo "stdout" >&1
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And we can redirect to stderr with:

echo "stderr" >&2
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users

The users command shows all the users currently logged in.

To see all users on the system, we can check /etc/passwd .

useradd

To add a user to the system, we run useradd .

For instance, we run:

sudo useradd foo
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to add the foo user.

userdel

userdel lets us delete the user.

For example, we run:

`sudo` userdel `foo`
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to delete the foo user from the system.

groups

groups show all the groups of which the current user is a member.

We can see all groups in the /etc/group .

We shouldn’t change /etc/group unless we know what we’re doing.

groupadd

groupadd lets us add groups into our system.

We can run:

sudo groupadd foo
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to add the foo group.

groupdel

groupdel lets us delete a group.

We can run:

sudo groupdel foo
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to delete a group.

cmp

cmp gets the byte difference between 2 files.

For instance, we run:

cmp a b
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to get the byte difference between files a and b .

cut

cut lets us cut a line into sections on some delimited.

The -d flag lets us specify a delimiter.

-f specifies the field index to print.

For instance, we run:

printf "117.99.234.23" > c
cut -d'.' c -f1
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to print 117 onto the screen.

sed

sed lets us replace a string with another string in a file.

For instance, we runL

echo "old" | sed s/old/new/
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to remove old with new .

ssh

ssh lets us connect from one machine to another machine.

We run:

ssh –p <port> bob@1.2.3.4
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to connect to machine with IP address 1.2.3.4 with user bob .

scp

We can use scp to copy a file securely from one machine to another.

For instance, we can run:

scp –P <port> hello bob@1.2.3.4:~
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to copy the hello file from the machine with IP address 1.2.3.4.

rsync

The rsync utility lets us copt files with the least amount of data possible being transmitted.

This is done by looking at changes between files.

For instance, we run:

rsync -av ../s/* .
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to sync the files from the ../s directory with the current directory with rsync .

rsync also works over ssh .

We run:

rsync -avz -e "ssh -p <port>" bob@1.2.3.4:~/s/* .
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to copy the data over to the machine with IP 1.2.3.4.

Conclusion

We can print files, manipulate users and groups, and connect to other machines with some Linux commands.

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