How to execute a remote command over ssh with arguments?

Question

In my .bashrc I define a function which I can use on the command line later:

function mycommand() {
    ssh [email protected] cd testdir;./test.sh "$1"
}

When using this command, just the cd command is executed on the remote host; the test.sh command is executed on the local host. This is because the semicolon separates two different commands: the ssh command and the test.sh command.

I tried defining the function as follows (note the single quotes):

function mycommand() {
    ssh [email protected] 'cd testdir;./test.sh "$1"'
}

I tried to keep the cd command and the test.sh command together, but the argument $1 is not resolved, independent of what I give to the function. It is always tried to execute a command

./test.sh $1

on the remote host.

How do I properly define mycommand, so the script test.sh is executed on the remote host after changing into the directory testdir, with the ability to pass on the argument given to mycommand to test.sh?

This is unrelated to the main point, but you might want to use && instead of the semi-colon to join the commands executed on the remote host: cd testdir && ./test.sh "$1". With that form (because evaluation of && short-circuits in bash), if the cd fails the second command won't be executed, and you won't inadvertently run a different test.sh in user's homedir. — Alp
– Alp, Commented Aug 29, 2013 at 7:09

konsolebox · Accepted Answer · 2022-03-15 14:39:38Z

170

Do it this way instead:

function mycommand {
    ssh [email protected] "cd testdir;./test.sh \"$1\""
}

You still have to pass the whole command as a single string, yet in that single string you need to have $1 expanded before it is sent to ssh so you need to use "" for it.

Update

Another proper way to do this actually is to use printf %q to properly quote the argument. This would make the argument safe to parse even if it has spaces, single quotes, double quotes, or any other character that may have a special meaning to the shell:

function mycommand {
    printf -v __ %q "$1"
    ssh [email protected] "cd testdir;./test.sh $__"
}

When declaring a function with function, () is not necessary.
Don't comment back about it just because you're a POSIXist.

Starting Bash version 4.4, it can also be simplified to this:

function mycommand {
    ssh [email protected] "cd testdir;./test.sh ${1@Q}"
}

See ${parameter@operator} section in Shell Parameter Expansion.

edited Mar 15, 2022 at 14:39

answered Aug 29, 2013 at 5:32

konsolebox

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6 Comments

konsolebox Over a year ago

@JoSo Yes that's the basic of it so depending on usage the user can opt to sanitize the argument he needs it. With respect to basic ssh there's probably no better way - unless you do file transfers first, etc.

augurar Over a year ago

@JoSo Yes, a better approach would be to define a quote function like quote() { printf "'%q'" "$1"; }, and then do ssh user@host "cd testdir; ./test.sh $(quote "$1")"

Charles Duffy Over a year ago

@augurar, almost, but %q results are self-quoting; surrounding them with literal quotes isn't necessary or correct. printf -v arg_str '%q ' "$1"; ssh user@host "cd testdir; ./test.sh $arg_str" suffices.

konsolebox Over a year ago

@CharlesDuffy Why do you need to add space though?

Charles Duffy Over a year ago

@konsolebox, for just the immediate case, don't really, but that way the idiom scales if more arguments are added rather than smushing them all together.

|

Aviv · Accepted Answer · 2022-11-27 15:42:23Z

Solution: you want to be able connect to machine remotely using ssh protocol and trigger/run some actions outside.

on ssh use a -t flag, from documentation:

-t Force pseudo-terminal allocation.
This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu services. Multiple -t options force tty allocation, even if ssh has no local tty.

formula:

ssh -i <key-path> <user>@<remote-machine> -t '<action>'

Example: as administrator I want to be able to connect remotely into ec2 machines and trigger a revert process for a bad deployment on a several machines in a raw, moreover you better implement this action as an automation script that use ips as an arguments and running on different machines in parallel.

ssh -i /home/admin/.ssh/key [email protected] -t 'cd /home/application && make revert'

Cyril Duchon-Doris · Accepted Answer · 2018-04-22 00:40:12Z

18

This is an example that works on the AWS Cloud. The scenario is that some machine that booted from autoscaling needs to perform some action on another server, passing the newly spawned instance DNS via SSH

# Get the public DNS of the current machine (AWS specific)
MY_DNS=`curl -s http://169.254.169.254/latest/meta-data/public-hostname`


ssh \
    -o StrictHostKeyChecking=no \
    -i ~/.ssh/id_rsa \
    [email protected] \
<< EOF
cd ~/
echo "Hey I was just SSHed by ${MY_DNS}"
run_other_commands
# Newline is important before final EOF!

EOF

edited Apr 22, 2018 at 0:40

answered Mar 14, 2018 at 10:50

Cyril Duchon-Doris

14.2k12 gold badges92 silver badges181 bronze badges

Comments

muratgozel · Accepted Answer · 2018-12-30 12:19:56Z

12

I'm using the following to execute commands on the remote from my local computer:

ssh -i ~/.ssh/$GIT_PRIVKEY user@$IP "bash -s" < localpath/script.sh $arg1 $arg2

answered Dec 30, 2018 at 12:19

muratgozel

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1 Comment

gdm Over a year ago

the script is remote not local

Mathieu Barbot · Accepted Answer · 2022-02-18 22:51:19Z

-3

A little trick for me, using the "bash -s" they said they allow POSITIONAL ARGS but apparently the $0 is already reserved for whatever reason... Then using twice the same args rocks like so:

ssh user@host "bash -s" < ./start_app.sh -e test -e test -f docker-compose.services.yml

answered Feb 18, 2022 at 22:51

Mathieu Barbot

1734 bronze badges

1 Comment

gdm Over a year ago

the script is remote not local

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