How to Run Command Using SSH On Remote Machine?

There are different ways to run multiple commands on a remote Unix server using SSH. This article shows the most straightforward and easy approach to SSH and runs multiple commands in using the bash shell.

Single-line command

Executing a single command:

ssh user@server ls

Executing multiple commands, inlined, isolated with ;

ssh user@server ls; pwd; apt update

Executing a command with sudo

ssh user@server sudo apt update
sudo: no tty present and no askpass program specified

sudo requires interactive shell, it can be enabled with -t option.

ssh -t user@server sudo ls /root
[sudo] password for user:

Multi-line command with variables expansion

Let's say you have a variable VAR1 that you want to run on the remote server. For example, let's consider the following snippet:

VAR1="Variable 1"
ssh user@server '
ls
pwd
if true; then
    echo "True"
    echo $VAR1      # <-- it won't work
else
    echo "False"
fi
'

Here SSH will not allow us to run that variable with this method. To make variables expansion work, use bash -c.

VAR1="Variable 1"
ssh user@server bash -c "'
ls
pwd
if true; then
    echo $VAR1
else
    echo "False"
fi
'"

Multi-line command from local script

Use stdin redirection to run a local script using SSH.  Let's say you have a script.sh, and it has the following commands.

ls
pwd
hostname

Now to run it using SSH, use the following snippet:

ssh user@server < script.sh

Multi-line command using Heredoc

Heredoc is presumably the most helpful approach to execute multi-line commands on a remote machine. Likewise, variables extension works out-of-the-box.

VAR1="Variable 1"
ssh -T user@server << EOSSH
ls
pwd
if true; then
  echo $VAR1
else
  echo "False"
fi
EOSSH

If you need to assign variables inside the heredoc block, put the opening heredoc in single quotes.

ssh user@server <<'EOSSH'
VAR1=`pwd`
echo $VAR1

VAR2=$(uname -a)
echo $VAR2

EOSSH

Using the above snippet, you may get this below warning message:

Pseudo-terminal will not be allocated because stdin is not a terminal.

You can disable by adding -T parameter to the SSH command.

ssh -T user@server <<'EOSSH'
VAR1=`pwd`
echo $VAR1

VAR2=$(uname -a)
echo $VAR2

EOSSH