Shell Programming and Scripting

HI All,

I have one file like this

Code:

export count
------------------
0
src_sys   max rec(upd_dt)
----------- -------------
bkba          30-oct-2014
hjbs           30-oct-2014

i have one script which is provided by client and am trying to under stand how it is executing as am not aware of so much of awk functionality. Please help me how below command executing and appreciate if some one can explain me.

Code:

awk 'uc&&!--uc;/export count/{uc=2} filename

otupt of this comnand is as in above mentioned file count is 0

Code:

0

please explain me what this command is doing.

second command is

Code:

awk '/src/{c=3}c&&c--' filename

output is

Code:

src_sys   max rec(upd_dt)
----------- -------------
bkba          30-oct-2014
hjbs           30-oct-2014

awk 'uc&&!--uc;/export count/{uc=2} filename:
For every line uc, defaulting to 0 (== FALSE), is evaluated. The second condition is not evaluated, due to "short circuit evaluation".
When "export count" is found uc will be set to 2.
For the next line, uc == 2 == TRUE, !(--uc == 1 == TRUE) == FALSE, nothing happens.
For the second next line, uc ==1 == TRUE, !(--uc == 0 == FALSE) == TRUE, so the default action for TRUE patterns, i.e. print, will be executed, which yields "0".

A similar logic holds for your second example, who's step-by-step explanation I leave up to you for learning purposes.

sorry Rudic, i did not get first command execution, appreicate if you can explian me more for this special

uc&&!--uc

Read it like

Code:

uc && !(--uc) {print}
pattern       {action}

and reread my post.

what -- this is doing in front of uc

i agree when export found it become uc =2 as per condition

then

Code:

uc && ! (-- uc )
2 && ! (how uc becomes 1 here as per ur condition )

while evaluating first line after export word finding

-- is a (here: pre-) decrement operator known in many programming languages like C, awk, etc. It decrements uc by 1 before referencing it. I'd recommend reading man awk ASAP.