how to find out common columns and its records from two files using awk - bash

Question

I have two files:
File 1:
id|name|address|country
1|abc|efg|xyz
2|asd|dfg|uio
File 2(only headers):
id|name|country
Now, I want an output like:
OUTPUT:
id|name|country
1|abc|xyz
2|asd|uio
Basically, I have a user record file(file1) and a header file(file2).Now, I want to extract only those records from (file1) whose columns match with that in the header file.
I want to do this using awk or bash.
I tried using:
awk 'BEGIN { OFS="..."} FNR==NR { a[(FNR"")] = $0; next } { print a[(FNR"")], $0 > "test.txt"}' header.txt file.txt
and have no idea what to do next.
Thank You

Answer 1

Following awk may help you on same.
awk -F"|" 'FNR==NR{for(i=1;i<=NF;i++){a[$i]};next} FNR==1 && FNR!=NR{for(j=1;j<=NF;j++){if($j in a){b[++p]=j}}} {for(o=1;o<=p;o++){printf("%s%s",$b[o],o==p?ORS:OFS)}}' OFS="|" File2 File1
Adding a non-one liner form of solution too now.
awk -F"|" '
FNR==NR{
for(i=1;i<=NF;i++){
a[$i]};
next}
FNR==1 && FNR!=NR{
for(j=1;j<=NF;j++){
if($j in a){ b[++p]=j }}
}
{
for(o=1;o<=p;o++){
printf("%s%s",$b[o],o==p?ORS:OFS)}
}
' OFS="|" File2 File1
Edit by Ed Morton: FWIW here's the same script written with normal indenting/spacing and a couple of more meaningful variable names:
BEGIN { FS=OFS="|" }
NR==FNR {
for (i=1; i<=NF; i++) {
names[$i]
}
next
}
FNR==1 {
for (i=1; i<=NF; i++) {
if ($i in names) {
f[++numFlds] = i
}
}
}
{
for (i=1; i<=numFlds; i++) {
printf "%s%s", $(f[i]), (i<numFlds ? OFS : ORS)
}
}

Answer 2

with (lot's of) unix pipes as Doug McIlroy intended...
$ function p() { sed 1q "$1" | tr '|' '\n' | cat -n | sort -k2; }
$ cut -d'|' -f"$(join -j2 <(p header) <(p file) | sort -k2n | cut -d' ' -f3 | paste -sd,)" file
id|name|country
1|abc|xyz
2|asd|uio

Answer 3

Solution using bash>4:
IFS='|' headers1=($(head -n1 $file1))
IFS='|' headers2=($(head -n1 $file2))
IFS=$'\n'
# find idxes we want to output, ie. mapping of headers1 to headers2
idx=()
for i in $(seq 0 $((${#headers2[#]}-1))); do
for j in $(seq 0 $((${#headers1[#]}-1))); do
if [ "${headers2[$i]}" == "${headers1[$j]}" ]; then
idx+=($j)
break
fi
done
done
# idx=(0 1 3) for example
# simple join output function from https://stackoverflow.com/questions/1527049/join-elements-of-an-array
join_by() { local IFS="$1"; shift; echo "$*"; }
# first line - output headers
join_by '|' "${headers2[#]}"
isfirst=true
while IFS='|' read -a vals; do
# ignore first (header line)
if $isfirst; then
isfirst=false
continue;
fi;
# filter from line only columns with idx indices
tmp=()
for i in ${idx[#]}; do
tmp+=("${vals[$i]}")
done
# join ouptut with '|'
join_by '|' "${tmp[#]}"
done < $file1

Answer 4

This one respects the order of columns in file1, changed the order:
$ cat file1
id|country|name
The awk:
$ awk '
BEGIN { FS=OFS="|" }
NR==1 { # file1
n=split($0,a)
next
}
NR==2 { # file2 header
for(i=1;i<=NF;i++)
b[$i]=i
}
{ # output part
for(i=1;i<=n;i++)
printf "%s%s", $b[a[i]], (i==n?ORS:OFS)
}' file1 file2
id|country|name
1|xyz|abc
2|uio|asd
(Another version using cut for outputing in revisions)

Answer 5

This is similar to RavinderSingh13's solution, in that it first reads the headers from the shorter file, and then decides which columns to keep from the longer file based on the headers on the first line of it.
It however does the output differently. Instead of constructing a string, it shifts the columns to the left if it does not want to include a particular field.
BEGIN { FS = OFS = "|" }
# read headers from first file
NR == FNR { for (i = 1; i <= NF; ++i) header[$i]; next }
# mark fields in second file as "selected" if the header corresponds
# to a header in the first file
FNR == 1 {
for (i = 1; i <= NF; ++i)
select[i] = ($i in header)
}
{
skip = 0
pos = 1
for (i = 1; i <= NF; ++i)
if (!select[i]) { # we don't want this field
++skip
$pos = $(pos + skip) # shift fields left
} else
++pos
NF -= skip # adjust number of fields
print
}
Running this:
$ mawk -f script.awk file2 file1
id|name|country
1|abc|xyz
2|asd|uio