ssh-exec.md

ssh-exec

Purpose

Execute a script on a remote host.

Syntax

Syntax: ssh-exec [--verbose] [-i INTERPRETER ...] [-d] [-q] [-b] [-e ENV] [-v] host script [arg [arg ...]]

Options and arguments

Option	Description	Default
-i, --interpreter	Run the script with a specific interpeter. Arguments can be specified in the same argument.	The remote host detects the interpreter, possibly through bang-slash comment
-d, --docker	Treat remote host as a Docker container	ssh is used to access the remote host
-q, --quiet	Uses the ssh --quiet option. Not applicable with --docker	Extra messages may come from ssh
-e key=value, --env key-value	Defines an environment variable and value to be used while the script runs. Multiple occurrences can be used for multiple variables.	No extra environment variables are used
-b, --become	Use sudo on the remote host to become root before running script	root it not used - an unprivileged user is likely used
-v, --verbose	Enable verbose debugging	Debugging is not enabled

Example

Bash script

Here's a sample Bash script with which I'll demonstrate:

$ cat ~/tmp/HelloWorld.sh
#! /usr/bin/env bash

echo "Hello, uid $(id -u) from bash world"
echo
echo "Number of arguments: $#"
curr=1
while [ $# -gt 0 ]
do
  echo "$curr: $1"
  shift 1
  let 'curr=curr+1'
done

if env | grep -q ^FOO
then
  echo
  env | grep ^FOO
fi
$

ssh examples

$ ssh-exec -e FOO=bar localhost ~/tmp/HelloWorld.sh 1 2 3
Hello, uid 1000 from bash world

Number of arguments: 3
1: 1
2: 2
3: 3

FOO=bar
$ ssh-exec -b -e FOO=bar localhost ~/tmp/HelloWorld.sh 1 2 3
Hello, uid 0 from bash world

Number of arguments: 3
1: 1
2: 2
3: 3

FOO=bar
$ ssh-exec -i 'bash -x' -e FOO=bar localhost ~/tmp/HelloWorld.sh 1 2 3
++ id -u
Hello, uid 1000 from bash world

+ echo 'Hello, uid 1000 from bash world'
+ echo
Number of arguments: 3
+ echo 'Number of arguments: 3'
+ curr=1
+ '[' 3 -gt 0 ']'
1: 1
+ echo '1: 1'
+ shift 1
+ let curr=curr+1
+ '[' 2 -gt 0 ']'
+ echo '2: 2'
2: 2
+ shift 1
+ let curr=curr+1
+ '[' 1 -gt 0 ']'
+ echo '3: 3'
3: 3
+ shift 1
+ let curr=curr+1
+ '[' 0 -gt 0 ']'
+ env
+ grep -q '^FOO'

+ echo
+ env
+ grep '^FOO'
FOO=bar
$

Docker example

I'm using an Alpine container which doesn't come with a bash interpreter so I'll override the slash-bang comment:

$ ssh-exec -i sh -e FOO=bar -d alpine ~/tmp/HelloWorld.sh 1 2 3
Hello, uid 0 from bash world

Number of arguments: 3
1: 1
2: 2
3: 3

FOO=bar
$

$ ssh-exec -e FOO=bar localhost ~/tmp/HelloWorld.sh 1 2 3
Hello, uid 1000 from bash world

Number of arguments: 3
1: 1
2: 2
3: 3

FOO=bar
$ ssh-exec -b -e FOO=bar localhost ~/tmp/HelloWorld.sh 1 2 3
Hello, uid 0 from bash world

Number of arguments: 3
1: 1
2: 2
3: 3

FOO=bar
$

Python script

Here's a sample Python script with which I'll demonstrate:

$ cat ~/tmp/HelloWorld.py
#! /usr/bin/env python

import os
import sys

print(f'Hello uid {os.getuid()}, Python world\n')

print(f'Number of arguments: {len(sys.argv)-1}')
for arg in range(1, len(sys.argv)):
  print(f'{arg}: {sys.argv[arg]!r}')

foo_env = {key:os.environ[key] for key in os.environ.keys() if key.startswith('FOO')}
if foo_env:
  print()
  for (key, value) in foo_env.items():
    print(f'{key}={value!r}')
$

Example

$ ssh-exec localhost ~/tmp/HelloWorld.py
Hello uid 1000, Python world

Number of arguments: 0
$

Notes

• The script is most effective with ssh hosts if you enable password-less ssh using keys