Confusing sed error message


 
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# 8  
Old 12-16-2018
Quote:
Originally Posted by Ralph
...
Code:
while read $LINE ; do
.
.
.

I got the idea because while read works line by line from the beginning of the file the swapped line is always located behind the other one so if I remove it read will never see it. But apparently the entire original file is still available to read no matter what I remove.

Is there is a better approach?

You might want to read the input data into several variables, not just the one $LINE. Like while read V1 DIR1 DIR2 V2, and the operate on the two DIR variables...
This User Gave Thanks to RudiC For This Post:
# 9  
Old 12-17-2018
Thanks. That worked well.

I also modified my script to avoid duplicates in the first place, using an array to save filenames and compare them to incoming new ones.

It is reassuring that the results are the same as with awk '!A[$2,$3]++ && !A[$3,$2]++' file.

Now spending some time with awk to figure out what that actually does...

--- Post updated at 10:00 PM ---

Quote:
Originally Posted by Scrutinizer
Assuming the fields in your input file are whitespace separated, you could try this approach:
Code:
awk '!A[$2,$3]++ && !A[$3,$2]++' file

Hm...
I converted this, with some trial and error, into what I think an awk program would look like:
Code:
#!/usr/bin/awk -f
{
#       !A[$2,$3]++ && !A[$3,$2]++
        !A[$2 " " $3]++ && !A[$3 " " $2]++
}
END {
        for ( i in A ){
                if ( A[i] == 1 )
                print A[i], i;
        }
}

Two questions:
1) If I keep the A[$2,$3] and A[$3,$2] then the output produces a funny character between the two filenames but the command line version works fine. What is the problem?
2) How does the command line version know to print only those keys (i) for which the count is 1?

I'm using GNU Awk 4.1.4, API: 1.1 (GNU MPFR 3.1.5, GNU MP 6.1.2)

(I'll figure it out somehow but it's getting late and it doesn't hurt to ask.)
Thanks.

Last edited by Ralph; 12-17-2018 at 06:29 PM..
# 10  
Old 12-18-2018
awk does not print a key equal to 1. It's print when the key is zero. Post increment ++
Value is first equal to 0 and then 1, 2, etc.
0 == fals == no print
1 == true == print
but the sign of inversion ! makes so
!0 == true == print
!1 == false == no print
!2 == false == no print
when you enclose the script in brackets you can not put an inversion sign
In the body it does not work

Last edited by nezabudka; 12-18-2018 at 08:20 AM..
# 11  
Old 12-18-2018
Quote:
Originally Posted by Scrutinizer
Assuming the fields in your input file are whitespace separated, you could try this approach:
Code:
awk '!A[$2,$3]++ && !A[$3,$2]++' file

Quote:
Originally Posted by nezabudka
awk does not print a key equal to 1. It's print when the key is zero. Post increment ++
Value is first equal to 0 and then 1, 2, etc.
0 == fals == no print
1 == true == print
but the sign of inversion ! makes so
!0 == true == print
!1 == false == no print
!2 == false == no print
The keys are '$3,$2' and '$2,$3'. Right? The values after the entire file has been processed are either 2 or 1.

What I mean is when I leave out the END block nothing get's printed.
Code:
#!/usr/bin/awk -f
{
       !A[$2,$3]++ && !A[$3,$2]++
}

What awk program will deliver the same result as the one-liner awk !A[$2,$3]++ && !A[$3,$2]++ file ?

(I suspect I'm missing something obvious.)

Last edited by Ralph; 12-18-2018 at 08:31 AM..
# 12  
Old 12-18-2018
I probably corrected my message when you answered
Excuse me. re-read it please
Code:
awk '1' file
awk '0' file
awk '!0' file

--- Post updated at 13:09 ---
print array
Code:
awk '{A[$2" "$3]++; A[$3" "$2]++} END {for(i in A) print i}'

--- Post updated at 13:15 ---

in
Code:
'!A[$0]++'

awk doesn't print the array, it just gets the true or false for output or not for evry line

Last edited by nezabudka; 12-19-2018 at 12:06 AM..
# 13  
Old 12-18-2018
Quote:
Originally Posted by Ralph
The keys are '$3,$2' and '$2,$3'. Right? The values after the entire file has been processed are either 2 or 1.

What I mean is when I leave out the END block nothing get's printed.
Code:
#!/usr/bin/awk -f
{
       !A[$2,$3]++ && !A[$3,$2]++
}

What awk program will deliver the same result as the one-liner awk !A[$2,$3]++ && !A[$3,$2]++ file ?

(I suspect I'm missing something obvious.)
You would need to leave out the braces:

Code:
#!/usr/bin/awk -f
!A[$2,$3]++ && !A[$3,$2]++

Everything in awk has the form condition{action}. If the condition evaluates to 1 then the action is performed. If the condition is omitted then the default condition is 0, so the action is not performed. If the action is omitted then - if the condition is 1 - the default action is performed, which is {print $0}, which is "print the record", by default a line of the input file.

Since there is just a condition with the default action, in this case there are no braces.

Last edited by Scrutinizer; 12-18-2018 at 10:20 PM..
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