bash ini parser

In some situations i like to use INI files as configuration files, as python do. But bash do not provide a parser for these files, obviously you can use a awk code or a couple of sed calls, but if you are bash-priest and do not want to use nothing more, then you can try the following obscure code:

cfg.parser () {
    IFS=$'\n' && ini=( $(<$1) )              # convert to line-array
    ini=( ${ini[*]//;*/} )                   # remove comments
    ini=( ${ini[*]/#[/\}$'\n'cfg.section.} ) # set section prefix
    ini=( ${ini[*]/%]/ \(} )                 # convert text2function (1)
    ini=( ${ini[*]/=/=\( } )                 # convert item to array
    ini=( ${ini[*]/%/ \)} )                  # close array parenthesis
    ini=( ${ini[*]/%\( \)/\(\) \{} )         # convert text2function (2)
    ini=( ${ini[*]/%\} \)/\}} )              # remove extra parenthesis
    ini[0]=''                                # remove first element
    ini[${#ini[*]} + 1]='}'                  # add the last brace
    eval "$(echo "${ini[*]}")"               # eval the result
}

And then you can parse your ini files as following:

# parse the config file called 'myfile.ini', with the following
# contents::
#   [sec2]
#   var2='something'
cfg.parser 'myfile.ini'

# enable section called 'sec2' (in the file [sec2]) for reading
cfg.section.sec2

# read the content of the variable called 'var2' (in the file
# var2=XXX). If your var2 is an array, then you can use
# ${var[index]}
echo "$var2"

Unfortunately, the cfg.parser() function do no support embedded spaces
in section names… yet

tcptraceroute was another friend of the network administrator. Probably you known classical traceroute, which use the TTL field in IP header to determinate the hops in the route to a specific destination. In each hop the TTL value is decreasing (according to internet protocol), and when TTL is equal to cero, a ICMP is returned to sender IP. So, the classical traceroute technique, send a UDP packet with TTL field setted to 1, and get the IP address of the first hop from returned ICMP, and likewise for other hops.

Unfortunately, today many host are firewalled and ICMPs are blocking. The classical traceroute design fails, and we only obtain a list of useless “*”. The tcptraceroute use TCP packets instead of UDP packets, and try to connect to usual port enabling the SYN flag. If port is closed, a RST flag is returned, and if port is open then return an ACK flag. So we don’t need ICMPs anymore.

ssh socket

When work using a “cheap” wireless network (yes, I still have kind neighbours), each new ssh connection takes a lot of time, because a new authentication is required from the peer, but what happens if I already connected? In theory no new re-authentication is necessary, you can use existing socket to send data over the same channel of the previous connection. To enable socket manager, put the following lines in your ~/.ssh/config file:

Host *
  ControlMaster auto
  ControlPath ~/.ssh/socket-%r@%h:%p

Some situations may freeze your ssh connection, for example when the network goes down before close connection and timeout is reached, in this case the socket will also be frozen, and new connections to the same destination are no possible. Only need to remove the socket file in ~/.ssh/ directory and kill the previous session.