Given a host, match to the actual ssh hostname per standard ssh_config files.

find_ssh_host_name.py

#!/usr/bin/env python

"""

find_ssh_host_name.py

Given a hostname on the command line, return the hostname from standard ssh_config sources on stdout. 


(c) 2011 Barry Allard <[email protected]>

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

http://www.opensource.org/licenses/mit-license.php

"""

import sys
import os
import os.path
import re

def parse_ssh_config(f):
    """
    Parse an ssh_config file per http://linux.die.net/man/5/ssh_config
 

    f is read a file until EOF
  
    Returns a tuple = ( { global options } , { per-host options } )
    """
    # Read file as a list of strings.
    lines = f.readlines()

    # Remove all comments.
    lines = map(lambda line: re.sub('#.*$', '', line), lines)

    # Strip all whitespace, right and left sides.
    lines = map(str.strip, lines)

    # Remove all lines with no remaining characters.
    lines = [ line for line in lines if len(line) > 0 ]

    # Split on = or whitespace as a list of list of strings.
    newlines = []
    choice = re.compile('^[^\s]*=', flags=re.LOCALE)
    for line in lines:
        if choice.match(line):
            newline = re.split('=', line, maxsplit=1, flags=re.LOCALE)
        else:
            newline = re.split('\s', line, flags=re.LOCALE)
        newlines.append(newline)
    del lines
    lines = newlines

    # Title Case the first element
    for line in lines:
        line[0] = line[0].title()

    # Global options
    ssh_globals = {}
    # Options per host
    ssh_hosts = []
    # Name of current host
    ssh_host = None
    # Options list of current host (dict)
    ssh_host_options = None

    for line in lines:
        key = line[0]
        value = ' '.join(line[1:])
        if key == 'Host':
            if ssh_host:
                ssh_hosts.append((ssh_host,ssh_host_options))
                ssh_host = None
                ssh_host_options = None
            ssh_host = value
            ssh_host_options = {}
        elif ssh_host:   
            ssh_host_options[key] = value 
        else: # global section
            ssh_globals[key] = value
    # Add remaining open host options
    if ssh_host:
        ssh_hosts.append((ssh_host,ssh_host_options))
        ssh_host = None
        ssh_host_options = None
    return (ssh_globals, ssh_hosts)


def find_host(host, ssh_config):
    ssh_globals, ssh_hosts = ssh_config
    for cur_host, cur_host_options in ssh_hosts:
        cur_host = '(?i)'+cur_host.replace('.', '\\.').replace('*','.*')+'$'
        if re.match(cur_host, host) and cur_host_options.has_key('Hostname'):
            return cur_host_options['Hostname'] 
    return None


def try_files(func, file_list):
    f = None
    try: 
        for file_name in file_list:
            if os.path.exists(file_name):
                f = file(file_name,'r')
                result = func(f)
                f.close()
                f = None
                if result:
                    return result
    finally:
        if f:
            f.close()
            f = None

def main():
    host = sys.argv[1]

    ssh_config_files = [ 
        os.path.join(os.environ['HOME'], '.ssh', 'config'),   # per user
        os.path.join('/', 'etc', 'ssh', 'ssh_config'),        # system-wide (Linux and *BSD)
        os.path.join('/', 'private', 'etc', 'ssh_config'),    # system-wide (Mac)
    ]

    result = try_files(lambda f: find_host(host, parse_ssh_config(f)), ssh_config_files)
    print result or host
    return result

if __name__ == "__main__":
    result = main()
    sys.exit(int(not result))