Shell Programming and Scripting

$ cat file1
2
3

$ cat file2
1
2
3
4
5
6

awk '
NR==FNR {A[$1]; next}
($1 in A)
' file1 file2
2
3

>file1

awk '
NR==FNR {A[$1]; print FILENAME,$1; next}
($1 in A)
' file1 file2

awk '
FILENAME=="file1" {A[$1]; print FILENAME,$1; next}
($1 in A)
' file1 file2

awk '
F==0 {A[$1]; print FILENAME,$1; next}
($1 in A) {print}
' file1 F=1 file2

awk '
BEGIN {f=FILENAME}
FILENAME==f {A[$1]; f=FILENAME; next}
($1 in A)
' file1 file2

awk '
FILENAME==f {A[$1]; f=FILENAME; next}
($1 in A)
' f=file1 file1 file2

awk '
BEGIN {	printf("ARGV[0]=%s\n", ARGV[0])
	for(i = 1; i < ARGC; i++)
		if(ARGV[i] ~ /=/)
			printf("ARGV[%d]=%s: assignment\n", i, ARGV[i])
		else {	printf("ARGV[%d]=%s: file operand\n", i, ARGV[i])
			if(!f1)	f1 = ARGV[i]
		}
	print ""
}
FILENAME == f1 {
	# Process lines from 1st file here...
	printf("From 1st file(%s); %s\n", f1, $0)
	next
}
{	# Process remaining files here...
	printf("From subsequent file(%s): %s\n", FILENAME, $0)
}' FS=, empty_file OFS='|' file1 FS='|' file2

f1 line1
f1 line2

f2 line1
f2 line2

ARGV[0]=awk
ARGV[1]=FS=,: assignment
ARGV[2]=empty_file: file operand
ARGV[3]=OFS=|: assignment
ARGV[4]=file1: file operand
ARGV[5]=FS=|: assignment
ARGV[6]=file2: file operand

From subsequent file(file1): f1 line1
From subsequent file(file1): f1 line2
From subsequent file(file2): f2 line1
From subsequent file(file2): f2 line2

}' FS=, OFS='|' file1 FS='|' file2

ARGV[0]=awk
ARGV[1]=FS=,: assignment
ARGV[2]=OFS=|: assignment
ARGV[3]=file1: file operand
ARGV[4]=FS=|: assignment
ARGV[5]=file2: file operand

From 1st file(file1); f1 line1
From 1st file(file1); f1 line2
From subsequent file(file2): f2 line1
From subsequent file(file2): f2 line2