python: import function

This is interesting to me. We can import only a particular function of a module inside python

Say there is a function boto.ec2.regions()

So I would write

>>> import boto.ec2
or
>>> from boto import ec2

>>> boto.ec2.regions()
or
>>> ec2.regions()

But we can also write

>>> from boto.ec2 import regions

>>> regions()

I had this scenario. Inside my python file I had import my util file. In the util file I had the above import.

from boto.ec2 import regions

So in my python file I could write

import util

util.regions()

Awesome right??

linux: logging top processes by cpu or memory

I wanted to log the processes consuming cpu and memory

First thought was to use top in the batch mode (-b).
-c to show the process name.
-n 1 to capture for 1, to run for 1 frame
   
$ top -b -c -n 1 > top_$(date +"%Y-%m-%d_%H%M").log

But I was not getting the complete process/command name.

Later I  used the below technique and it was quite helpful

#!/bin/bash

log_file=top_$(date +"%Y-%m-%d_%H%M").log
echo 'user    %cpu    %mem    pid    elapsed time    command' > $log_file
echo ' =========== CPU ===========' > $log_file
ps -eo user,pcpu,pmem,pid,etime,command | sort -rn -k2 | head -11 > $log_file
echo ' ========== MEMORY ==========' >> $log_file
ps -eo user,pcpu,pmem,pid,etime,command | sort -rn -k3 | head -11 >> $log_file

Observation:

1. 'ps aux' is a wonderful command

2. ps command itself has --sort <fieldname>, but there is no reverse sorting

bash script: arithmetic comparison

Arithmetic in BASH is integer math only. You can't do floating point math in Bash; if you need that capability, see Bash FAQ #22.

Remember few tricks

1. use [[ .. ]] for strings and files

2. use (( .. )) for numbers

To compare arithmetic numbers use bc function

$(echo "1.4 < 2.5" | bc)

> and < is for ASCII comparison and so 100 > 75 is false

-gt, -lt is only integer comparison.

This works for me

    if (( $(echo "$mem_util > 75" | bc) == 1 ))
    then
        ...
    fi

I am wondering why there was no floating point support??

References:

http://mywiki.wooledge.org/ArithmeticExpression

http://mywiki.wooledge.org/BashFAQ/031

linux: complete command

I have my .ssh/config with a lot of connection names. What would be better than to have auto complete with ssh <TAB> <TAB>

Added this line to my bash profile and I was good to go.

complete -W "$(awk '/^\s*Host\s*/ { sub(/^\s*Host /, ""); print; }' ~/.ssh/config)" ssh

man complete

There is a lot that human can do, for everything else there is [shell] script :)

rsync - folder to folder

rsync is wonder utility to sync files.

I had a situation and I was sure the developer must have thought of it. And I was right :) He had solved it with a trailing /

rsync [option] /home/foo/bar dest:/home/foo

will sync bar directory of source into destinations /home/foo.

Note: this requires access to /home/foo

Suppose you have /bar under root / of the destination and you want to sync the same source. Now this will get tricky as it is rare to have open access to /. The solution is

rsync [option] /home/foo/bar/ dest:/bar

The trailing / in the source syncs everything under bar and fits the solution to the problem.

linux: RANDOM is so simple

I was impressed with $RANDOM in linux. Simply use $RANDOM to get a random number.

Shell script thingy

Did you know: Hypen, -, is not allowed in script variable names!

a="A"
b="B"

echo "$a_$b"

will print B??!!

it will treat $a_ as the first variable name.

To fix it

echo "${a}_${b}"