using getline, close in BEGIN

using awk 20040207

my understanding is that close(getline) resets awk to read an input
file again (as in `awk -F mydatafile.dat`) but my results are at odds
with that.

i want FILENAME in my output (stdout) header :

BEGIN {
getline
printf ("| data file : %15s \n", FILENAME )
close (getline) #<- also tried close(FILENAME), didn't work...?
}

.... that's great, until i use getline again to read data into awk from
the same file :

myvariable1 = $2
getline
myvariable2 = $2

.... if the BEGIN construct is employed, the effect is like awk skips
the first line. data file looks like this :

1 1234
2 2345
3 145
(... continues...)

if i leave out the BEGIN stuff, getline does what i want, so i suspect
my understanding is lacking sp. on using close and getline.

-bryan

On Fri, 4 Jul 2008 13:02:07 -0700 (PDT), salmonrushdee <bryanlepore@gmail.com> wrote:

>using awk 20040207
>
>my understanding is that close(getline) resets awk to read an input
>file again (as in `awk -F mydatafile.dat`) but my results are at odds
>with that.
>
>i want FILENAME in my output (stdout) header :
>
>BEGIN {
> getline
> printf ("| data file : %15s \n", FILENAME )
> close (getline) #<- also tried close(FILENAME), didn't work...?
>}
My experience is with gawk, I build a command string and use this pattern:

# select port names datafile
cmd = "if [ -r " service1 " ]; then echo y; else echo n; fi"
cmd | getline s; close(cmd)

or another:

cmd = "echo $(host -W " host_max_secs " " addr ")|tail -1"
cmd | getline name; close(cmd)

You need to close the entire access command? I think accessing FILENAME with
getline may come under Ed's 'don't do that', but I don't have reference url

Grant.
--
http://bugsplatter.mine.nu/

On 7/4/2008 3:02 PM, salmonrushdee wrote:
> using awk 20040207
>
> my understanding is that close(getline) resets awk to read an input
> file again (as in `awk -F mydatafile.dat`) but my results are at odds
> with that.
>
> i want FILENAME in my output (stdout) header :
>
> BEGIN {
> getline
> printf ("| data file : %15s \n", FILENAME )
> close (getline) #<- also tried close(FILENAME), didn't work...?
> }

getline is best avoided in general, see http://tinyurl.com/yn9ka9.

FILENAME isn't set in the BEGIN section because no file is being read there. To
print a header line prior to any output, just test for it being the first input
record:

NR==1 { printf "| data file : %15s \n", FILENAME }

Regards,

Ed.