<datruth29> hey
<datruth29> is the a session today?
<hemanth> yes
<hemanth> 20 mins from now
<datruth29> okay, just wanted to make sure :)
<hemanth> :)
<datruth29> ohhhhhhhhhhh that's right, i thought it was at 11:00 xDD
<hemanth> using the class script ;)?
<datruth29> i just logged on through p2pu, i'm going to start it up now
<datruth29> oh wait
<datruth29> are you talking about limpid?
<datruth29> or another script?
<hemanth> no i had made on script that would tell when the next class is
<hemanth> brb
<datruth29> okay
<datruth29> brb
<hemanth> back
* SourRust (473b12d5@gateway/web/freenode/ip.71.59.18.213) has joined #p2pu-webcraft/scripting-101
<hemanth> SourRust, hey :)
<SourRust> hey
<hemanth> Lets wait for 3 more mins?
<SourRust> k
<hemanth> Pablo cant make it to class today it seems
<SourRust> are we learning ruby, perl redirects because I was looking at the chat log and it look like u only taught error handling
<hemanth> yes, but the std{in.out,err} can be handled with that
<SourRust> k
<hemanth> ./my.rb 2>&1 > log
<hemanth> normally could be done
<hemanth> but the same, when we catch errors could be written to a file
<hemanth> with a File object
<hemanth> so either ways the intention is redirection
<hemanth> looking for something particular?
<SourRust> quick example or both i guess
<SourRust> of*
<hemanth> If you want to do it withing the script dircetly with the std{out,err} you could do stdout.reopen("out.txt", "w")
<hemanth> Example 1: ./my.rb 2>&1 > log
<hemanth> ^ Where nothing is handled by the script, but by the shell
<hemanth> Example 2:
<hemanth> stdout.reopen("out.txt", "w")
<hemanth> stderr.reopen("err.log", "w")
<hemanth> warn 'this goes to err stderr'
<hemanth> puts 'this goes to err'
<hemanth> That was with ruby along with, the last class try rescue block
<SourRust> k thx
<hemanth> With Perl, the first method and the last class try catch works, along with it..
<hemanth> open (STDOUT, ">outfile") or die "Can't open STDOUT: $!";
<hemanth> open (STDERR, ">>err.log") or die "Can't open STDERR: $!";
<hemanth> Fine :) ?
<SourRust> yup
<hemanth> >& also apply the std > >> >& applies
* hemanth has changed the topic to: Pipes and Filters BASH
<hemanth> today we are dealing with something that is very interesting and an integral part of the shell
<hemanth> So, why do one use pipe in day to day life?
<hemanth> note, not the programming pipe
<hemanth> just the normal pipe
<hemanth> ...
<SourRust> to get things to and from places
<hemanth> yes :) one of the most useful use of pipes
<hemanth> "A set of processes chained by their standard streams, so that the output of each process (stdout) feeds directly as input (stdin) to the next one." => Pipes
<hemanth> lets see how to use them
<hemanth> So, in BASH we have used few separators like ; & ||
<hemanth> between commands
<hemanth> logical and ,or also
<hemanth> | is called as the pipe symbol
<hemanth> we can run many commands in a single line like
<hemanth> cmd1;cmd2;cmd3
<hemanth> thats runs in a seq
<hemanth> i guess few you would have done something like cmd&
<hemanth> have you?
<SourRust> i haven't
<datruth29> doesn't that run the command in the background or something?
<datruth29> i forgot o.
<hemanth> cmd& will put it to bg as background process.
<hemanth> datruth29, yes correct
<hemanth> When one have a log data crunching to do and he doesn want to wait till it runs, but he just want the o/p
<hemanth> he can put it to bg
<hemanth> 'jobs' is a bulletin in bash
<hemanth> just type jobs and hit enter
<hemanth> what do u see?
* hemanth paste the chat logs so far to Lakshmi
<hemanth> jobs => Lists the active jobs. JOBSPEC restricts output to that job. Without options, the status of all active jobs is displayed.
<datruth29> nothing right now
<hemanth> ok :)
<datruth29> but i bet if i run a job in the background, i would see it with that command
<datruth29> :P
<hemanth> yes
<hemanth> indeed :)
<hemanth> when u say cmd&
<hemanth> you will see
<hemanth> [1] 1256
<hemanth> then cmd1&
<hemanth> you will see something like [2] 1356
<Lakshmi> Thanks. Sorry I am late
<hemanth> wild guess what [number] number might be?
<hemanth> Lakshmi, its ok :)
<hemanth> no guesses ?
<datruth29> the order the jobs were called in?
<hemanth> almost close, but what is the second number
<hemanth> [number] might be consider as order in which they are called, but what might be the other number
<datruth29> i have no idea
<datruth29> the process id? o.o
<hemanth> bingo
* hemanth sends chocolates to datruth29
<hemanth> job number ([1]) and a process identification number
<datruth29> chocolate @_@ yum
<hemanth> :)
<hemanth> but why does the shell output them?
<hemanth> there must be some reason right
<hemanth> and the reason, is....
<hemanth> we can send each process to bg and fg on our choice
<hemanth> bg => background and fg=>foreground
<hemanth> Move jobs to the background, using 'bg'
* Lakshmi has quit (Quit: Page closed)
<hemanth> bg places the jobs identified by each JOB_SPEC in the background, as if they had been started with '&'
<hemanth> 'fg' does the reverse
<hemanth> fine?
<SourRust> yup
<hemanth> now in the pipe symbol, in your keyboards, do you all notice that its divided [[ a gap between them ]] ?
* hemanth magnifies it
<hemanth> |
<hemanth>
<hemanth> |
<hemanth> notice that ?
<Lakshmi> Yes
<hemanth> why could that be so?
* hemanth don't think i'm doing some hardware course, but that is very meaningful symbol
* hemanth gives a clue : cmd1 | cmd2
* hemanth another clue, the answer is there in whatever i spoke till now
<hemanth> ??
<Lakshmi> The output of the first Cmd is input to the second one
<hemanth> yup :) the cmd1 output goes through the pipe to cmd2
* hemanth sends pipes to Lakshmi | | | | ...
<Lakshmi> :)
<hemanth> ls -lt | head
<hemanth> try that in the terminal
<SourRust> oh... I had to look at a different keyboard to see because my macbook doesn't have a split between the pipe symbol
<hemanth> SourRust, i was expecting this from a Mac boy
<SourRust> o_O
<hemanth> SourRust, did u think of apple jobs for jobs command? ;)
<hemanth> SourRust, at the end of the day mac's base is free BSD
<SourRust> ik
* hemanth sends apples to SourRust from now on ;)
<SourRust> but yea my keyboard does have the split so I was confuse for a second
<hemanth> So, what did ls -lt | head display
<SourRust> ls of folders/file with info attached to them
<hemanth> ls -lt | head
<SourRust> drwx------+ 6 Jeremy staff 204 Oct 16 03:06 Desktop <- but more
<hemanth> yes it displays the 10 newest files in the current directory.
<hemanth> :)
<hemanth> echo Hello HaCkErs | tr [:lower:] [:upper:]
<hemanth> try ^
<SourRust> all caps now
<hemanth> yup
<hemanth> echo Hello HaCkErs | tr [:upper:] [:lower:]
<Lakshmi> Yes
<hemanth> echo Hello | tr [a-z] [A-Z] can also be done
<hemanth> du | sort -nr
<hemanth> space consumption in sorted order
<Lakshmi> Yes
<hemanth> tr -dc A-Za-z0-9_ < /dev/urandom | head -c12 | xargs
<hemanth> my fav ^
<hemanth> create random passwords
<hemanth> here in these examples the second part of the pipe are called filters
<hemanth> as they do some filtering stuff for us
<hemanth> to make things easier and better
<hemanth> sort
<hemanth> uniq
<hemanth> grep
<hemanth> fmt
<hemanth> pr
<hemanth> head
<hemanth> tail
<hemanth> tr
<hemanth> sed
<hemanth> awk
<hemanth> are on of the most commonly used once
<hemanth> queries?
<SourRust> nope
<hemanth> So, pipes and filters are very useful in the shell
<hemanth> now, the challenge for you guys is
<hemanth> to do pipe and filter simulation with py,rb or pl
<hemanth> like the script takes in two or more commands
<hemanth> and does the piping
<hemanth> and also, you need to pick on of the filter and simulate it
<hemanth> say grep
<hemanth> grep => print lines matching a pattern
<hemanth> So, the choice is your; well and good if you can make them in all py,rb and pl
<hemanth> NOTE: Note using system calls
<hemanth> clear?
<Lakshmi> Ok
<hemanth> So, if no more doubts, this ends the pipes and filter with BASH :)
<hemanth> all clear?
<hemanth> SourRust, datruth29
<SourRust> yes pretty clear
<Lakshmi> Yes
<hemanth> do ping with a thread in the course with your doubts
<hemanth> as it will help others also
<datruth29> sorry, stepped away for a bit
<datruth29> but yes
<datruth29> pipes and filters
<datruth29> super powerful
<datruth29> and awesome
<datruth29> :D
<hemanth> :)
<hemanth> Just enjoy its power all
<hemanth> cya tomo
<SourRust> cya
<datruth29> later!
<hemanth> until then happy hacking
<Lakshmi> Cya thanks
<hemanth> logs will be up in mins