Shell Programming and Scripting

are the { } necessary ?

(couldn't this X=1 assignment be done outside the brace ?)

does X=1 set the value 1 into the first element of an array ?

I mean since X is not previously declared so how does awk determine a suitable type for it? or are they just (void)-like by default ?

pseudo code:

Code:

if number of fields in line is non-zero then X=1
if X is non zero then print line

In awk expresions that result in non-zero equate to true for more clarity we could rewrite as follows:

Code:

(NF != 0) {X=1}  (X != 0)

Also the default action in awk is to print the current line, the following is also the same:

Code:

(NF != 0) {X=1}  (X != 0) {print}

Edit:

Took a while to type my response so above probably repeats what was already said. To answer you question yes the {} are necesary awk consists of a number of

expression { action }

pairs. Expression can be null in which case action is always executed, otherwise expression needs to equate to true before the action(s) are performed.

Special expressions BEGIN and END equate to true before and after the file is processed.

Variables are null (or zero) before being assigned, no arrays are used here (arrays have [])

Yes, it's necessary to put it in brackets, otherwise it will be set without condition.

awk will type the variable by whatever you set it as first time, so yes it's "void-type". X is a scalar, not an array (X[1]=1 would make X an array).

Code:

awk 'p+=NF' infile

@Scru1Linizer

Does "p" has a special meaning or is it a random choice of variable name?
Could you please comment your code ?

default NF is 1 ?
so p=p+1 ?
what is the default value of p ? p=1 ?

so that would make start to print$0 from line 2 ?

NF refer to the number of field of the line (which is 1 by default unless another separator is set ) or does it refer to the field number/index (the default field is a line )?

Could this also be written like this (is it equivalent)?

Code:

awk 'p+=NF 1' infile

I am a little confuse between NF and NR can someone clarify a little (ok a record is supposed to be composed of field so NF should refer to something inside NR...)

By default, a line is a field ? or a record ? or both ? (1 record of 1 field ?)

Thanks in advance for your help

It is a random variable name. I could also have used:

Code:

awk x+=NF infile

The value for NF varies per line. When there is an empty line then NF (number of fields) equals zero, hence the variable stays 0 for the first few lines that are empty. The value of the variable determines if the record gets printed. The default record is a line. NR is something else, that is the line number.

Ok i got it
wasn't aware x would be kept between 2 line read (i though the condition was evaluated for each line so that x would be reset every time a line was read), so i wasn't understanding the use of += instead of = but i got it now (otherwise the empty line that are not the first one wouldn't have been printed...

Many Thanks !