gawk: Merge N files into one

ETC Microsoft Windows
1

hi all!

i'm an awk newbie and have been trying in vain to merge N files together.

ie.

file1.txt:

a b c
1 1 1
2 2 2
3 3 3
4 4 4

file2.txt:

a b c
5 5 5
6 6 6
7 7 7
8 8 8

file3.txt:

a b c
9 9 9
10 10 10

i want to end up with:

a b c
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
7 7 7
8 8 8
9 9 9
10 10 10

And i also like to check if the 2nd or 3rd file has diferente number of colums, it stops.

Thanks in advance.

BR.

2 
awk 'NR==1{print;next}FNR==1{next}1' file1.txt file2.txt file3.txt > outfile
1 Like
3

Thanks

But can I validate that the number of columns of each file is the same?

4

Yes, awk stores the number of the columns in the internal variable NF.

For example:

awk '{print FILENAME, NF}' file1.txt file2.txt file3.txt
5

can send me please the code integrated that before processing all files validate the headers - number of columns is equal in all.

Only creates or process the new merged file if the number of columns is equal in boths files.

6

This prints the filename and the number of columns if it has more or less columns then the first row:

awk 'NR==1{n=NF}NF != n{print FILENAME " has " NF " columns"} 'file1.txt file2.txt file3.txt
7

I believe that I did not explained well.

What I want is the following:

file1.txt:

a b c
1 1 1
2 2 2
3 3 3
4 4 4

file2.txt:

a b c
5 5 5
6 6 6
7 7 7
8 8 8

file3.txt:

a b c
9 9 9
10 10 10

i want to end up with:

a b c
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
7 7 7
8 8 8
9 9 9
10 10 10

but if the 3rd file was:

a b
9 9
10 10

the tool should not generate any files.

And can you explain what represent 1 in the code: {next}1'. I tried 2,3,etc numbers and it works.

Thanks for your time but I am a zero in gawk

8

An awk statement has the form:

condition {action}

Conditions in awk control the execution of actions and actions are executed when the condition is true (1, 2, 3 or any value other then 0 or "" ).
If the condition is true and there are no actions between braces, awk prints the current record by default.

Try this:

awk 'NR==1{
  print;nf=NF;next
}
FNR==1{next}
nf!=NF{
  system("rm -f outfile"); exit
}1' file1.txt file2.txt file3.txt > outfile
9

Thanks in advance.

If the files have the same number of columns it works fine.
But if any file does not have the same number of columns gives error

i have error:
'0 Is not recognized as an internal or external command, operable program or batch file.

10

I don't get any error.... try nawk instead of awk.

11

I'm working on windows so i change:

NR==1{
  print;nf=NF;next
}
FNR==1{next}
nf!=NF{
  system("del -f outfile"); exit
}1

and error is:

The process can not access the file because it is being used by othe
the process.

12

I don't use awk in windows... but you can use the code of post #4 to check the columns of the files and the code of post #2 to merge the file.

13

I've used gawk on Windows before, but I don't have it available now to play with. You could try using redirection within the script so you may close the file before trying to delete it, and/or storing the output in memory before dumping it into an output file. This shows the latter:

[mute@geek ~/temp/sameeribraimo]$ cat merge.awk
BEGIN {
        outfile=ARGV[--ARGC]
        print "output: " outfile
}
NR==1{nf=NF;a[r++]=$0}
NF!=nf{exit 1}
FNR!=1{a[r++]=$0}
END {for (i=0;i<r;i++) print a > outfile}

[mute@geek ~/temp/sameeribraimo]$ gawk -f merge.awk file?.txt output.txt
output: output.txt
[mute@geek ~/temp/sameeribraimo]$ cat output.txt
a b c
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
7 7 7
8 8 8
9 9 9
10 10 10
14

moving to Windows forum