Print the first column of multiple files using awk - awk

Question

I have 20 files, I want to print the first column of each file into a different file.I need 20 output files.
i have tried the following command, but this one puts all the output into a single file.
awk '{print $1}' /home/gee/SNP_data/20* > out_file
write the output to different files, i have 20 input files

Answer 1

1st solution: Could you please try following.
awk '
FNR==1{
if(file){
close(file)
}
file="out_file_"FILENAME".txt"
}
{
print $1 > (file)
}
' /home/gee/SNP_data/20*
Explanation: Adding explanation for above code.
awk ' ##Starting awk program here.
FNR==1{ ##checking condition if FNR==1 then do following.
if(file){ ##Checking condition if variable file is NOT NULL then do following.
close(file) ##Using close to close the opened output file in backend, to avoid too many opened files error.
} ##Closing BLOCK for if condition.
file="out_file_"FILENAME".txt" ##Setting variable file value to string out_file_ then FILENAME(which is Input_file) and append .txt to it.
} ##Closing BLOCK for condition for FNR==1 here.
{
print $1 > (file) ##Printing first field to variable file here.
}
' /home/gee/SNP_data/20* ##Mentioning Input_file path here to pass files here.
2nd solution: In case you need to get output files like output_file_1.txt ans so on then try following. I have created an awk variable named out_file where you could change your output file's name's initial too(as per your need).
awk -v out_file="Output_file_" '
FNR==1{
if(file){
close(file)
}
++count
file=out_file count".txt"
}
{
print $1 > (file)
}
' /home/gee/SNP_data/20*

Answer 2

Awk has a builtin redirection operator, you can use it like:
awk '{ print $1 > ("out_" FILENAME) }' /home/gee/SNP_data/20*
or, even better:
awk 'FNR==1 { close(f); f=("out_" FILENAME) } { print $1 > f }' /home/gee/SNP_data/20*
Former is just an example usage of redirection operator, latter is how to use it robustly.