Learning SSHScript Chapter 1
The SSHScript is in pure Python. Its capability is based on the Paramiko and subprocess. The SSHScript provides easy syntax for you. With the SSHScript you can embed shell commands in Python codes. It looks like writing a shell script in Python.
Installation
$pip install sshscript
or
$python3 -m pip install sshscript
Upgrading
$pip install sshscript --upgrade
Check Installation
This course needs the “sshscript” executable, let us check if it works before moving on. To check it, please type “sshscript [ENTER]” on your console.
$ sshscript
If your screen shows something like below, it works. (version number does not matter)
SSHScript Version:1.102
usage: sshscript [-h] [--run-order] [--script]...
SSHScript
positional arguments:
paths path of .spy files or folders
optional arguments:
-h, --help show this help message and exit
--run-order show the files to run in order...
--script show the converted python scri...
...
Usage Scenario
- Edit a file of python script which contains codes in the syntax of SSHScript. Maybe you can name it with the suffix “.spy” to distinguish it from regular python script. Then let the sshscript executable to run your .spy script.
- Import “sshscript module” in a regular .py file, then call function sshscript.runFile() or sshscript.runScript() to run scripts which contain codes in the syntax of SSHScript.
This lesson introduces Scenario 1. When you are familiar with Scenario 1, you are able to use the SSHScript in Scenario 2.
Hello World
Below is a chunk of Python script with SSHScript syntax. Let’s name it “hello.spy”.
# File content of the hello.spy
$ echo hello world
print($.stdout)
Run it from console by:
# On console, types "sshscript hello.spy"
$ sshscript hello.spy
# Output in console
hello world
If you are interested of the converted “regular” Python script, you can do it by:
# On console
$ sshscript hello.spy --script
# Output
001:try:
002: __b = """echo hello world """
003: __c = SSHScriptDollar(None,__b,locals(),globals(),inWith=0)
004: __ret = __c(0)
005:finally:
006: _c = __c
007:print(_c.stdout)
008:
It is not easy to understand. But you don’t need to. It is only useful in case of debugging. When you want to know the content of some line which was complained about in the traceback message.
Please be noted that only one line in the script:
$echo hello world
The SSHScript runs it and puts its stdout into the $.stdout. You can take the $.stdout as a regular variable. Just likes what the second line did:
print($.stdout)
It’s a regular Python script but prints a SSHScript-specific variable $.stdout. Let’s know more about the $.stdout.
$.stdout
Please be noted that there is a dot (.) behind the $.
$.stdout is a str variable. Its content is the output of stdout of the least execution of shell command. eg.
$echo hello world
assert $.stdout.strip() == 'hello world'
Since the “echo” outputs ”hello word” to the stdout. The content of $.stdout is “hello world\n”（with newline）. Because it is a str，appended by .strip() or other string functions are fine. eg.
$ls -l
for line in $.stdout.split('\n'):
cols = line.split()
if len(cols): print('filename=',cols[-1])
$.stderr
Please be noted that there is a dot (.) behind the $.
The $.stdout is paired with the $.stderr。The $.stderr is a str variable. Its content is the output of stderr of the least execution of shell command. eg.
# Content of stderr-testing.spy file
$ls -l /not-found-folder
print('Error:' + $.stderr)
# On console
$ sshscript stderr-testing.spy
#Output：
Error: ls: /not-found-folder: No such file or directory
Generally speaking, $.stderr is an empty string if the least shell command execution is successful. But it is not always so, for example, the “sudo” outputs its prompt “Password:” from stderr.
Hello World @Host
All the example codes on the above sections are run on localhost by subprocess module. What if you want to execute them on a remote host?
All you have to do is connecting the remote host by adding one line:
$.connect('yourname@host',password='password')
$ echo hello world
print($.stdout)
When you have two hosts, you can do it one by one:
# ssh from localhost ➜ host-a
$.connect('yourname@host-a',password='password-a')
$ echo hello world on host-a
print($.stdout)
$.close() # disconnect from host-a
# ssh from localhost ➜ host-b
$.connect('yourname@host-b',password='password-b')
$ echo hello world on host-b
print($.stdout)
$.close() # disconnect from host-b. this line is optional
In case that the host-b is behind the host-a. You have to take the host-a as a bridge to the host-b. It’s easy, just keep the connection to the host-a, don’t close it, then connect to host-b. Here you are:
# localhost ➜ host-a ➜ host-b
$.connect('yourname@host-a',password='password-a')
$.connect('yourname@host-b',password='password-b')
$ echo hello world
print($.stdout)
Usually, it is called “nested ssh”. With the SSHScript, you make a nested ssh with only 2 lines. No surprise, you can make a nested-nested ssh with 3 lines.
Of course, you can execute any commands on the connected host, not just saying hello.
$.connect('yourname@host-a',password='password-a')
$.connect('yourname@host-b',password='password-b')
# download file from host-b
$.download('/var/log/message')
# chekc disk uitilization
$ df
print($.stdout)
# check network connections
$ nestat -antu
print($.stdout)
# check who have been login this host
$ last -30
print($.stdout)
You can also do complex parsing on command’s output with Python
$.connect('yourname@host-a',password='password-a')
$.connect('yourname@host-b',password='password-b')
# Assume that you have a function to send SMS.
import sendsms
# Check the disk uitilizaion, and
# send a SMS notification if the utilization over 80%
$ df
for line in $.stdout.split('\n'):
cols = line.strip().split()
if len(cols) and cols[4][-1] == '%':
capacity = int(cols[4][:-1])
if capacity > 80:
sendsms(f'Warning:{cols[0]} has capacity over 80')
A .spy file is eventually a .py script file. In a .spy file, you are full-powered by Python.
The $.connect() supports “with” syntax. You can utilize this feature to make codes more readable. eg.
with $.connect('yourname@host-a',password='password-a') as _:
with $.connect('yourname@host-b',password='password-b') as _:
$ echo hello world
print($.stdout)
You don’t need to call $.close() in context of “with”. The above example can be written like this:
# ssh from localhost ➜ host-a
with $.connect('yourname@host-a',password='password-a') as _:
$ echo hello world on host-a
print($.stdout)
# ssh from localhost ➜ host-b
with $.connect('yourname@host-b',password='password-b') as _:
$ echo hello world on host-b
print($.stdout)
ssh connection with key
If you do ssh connection with key, you do not need to provide password. Just like this:
$.connect('yourname@host-a')
It is because the Paramiko would load the key from the default path. At least it works on my Macbook Pro. If It was not working for you, you can explicitly assign the key by giving its path, eg.
keypath = os.path.expanduser('~/.ssh/id_rsa')
# $.pkey() loads ssh key from file
pkey = $.pkey(keypath)
$.connect('yourname@host-a',pkey=pkey)
When jumping to a nested host by ssh with key, the pkey parameter is required.
$.connect('yourname@host-a')
# Please be noted that the given keypath is on the host-a, not the localhost.
keypath = '/home/yourname/.ssh/id_rsa'
pkey = $.pkey(keypath)
$.connect('yourname@host-b',pkey=pkey)
If you have already moved the key file from the host-a to the localhost. You should load the key before making connection to remote host.
keyA = $.pkey('keys/host-a/id_rsa')
keyB = $.pkey('keys/host-b/id_rsa')
$.connect('yourname@host-a',pkey=keyA)
$.connect('yourname@host-b',pkey=keyB)
The reason is that the $.pkey() loads key depending on its context. Under the context of having ssh connection, it looks for content on the connecting host.
Multiple commands in triple quotes
If you have many commands to run, you can write them into a triple quotes string. eg.
$'''
df
netstat -antu
last -30
'''