Shell Programming and Scripting

# where <TAB> would be a real tab:
while IFS="<TAB>" read a b c d; do echo $c; done < file.txt

awk -F"\t" '{print $3}' file.txt

while IFS="<TAB><TAB>" read ...

echo "$c"

while IFS=$'\t\t' read

#!/bin/ksh
while IFS='' read -r line
do	printf 'input:"%s"\n' "$line"
	d=${line##*	}
	line=${line%	*}
	c=${line##*	}
	line=${line%	*}
	b=${line##*	}
	line=${line%	*}
	a=${line##*	}
	printf 'a=%s,b=%s,c=%s,d=%s\n' "$a" "$b" "$c" "$d"
done < file.txt

a	b	all fields present	d
a		field 2 empty	d
	b	field 1 empty	d
		fields 1 & 2 empty	d
		fields 1, 2, & 4 empty	
a	b	c	d \
e	f	g	h

input:"a	b	all fields present	d"
a=a,b=b,c=all fields present,d=d
input:"a		field 2 empty	d"
a=a,b=,c=field 2 empty,d=d
input:"	b	field 1 empty	d"
a=,b=b,c=field 1 empty,d=d
input:"		fields 1 & 2 empty	d"
a=,b=,c=fields 1 & 2 empty,d=d
input:"		fields 1, 2, & 4 empty	"
a=,b=,c=fields 1, 2, & 4 empty,d=
input:"a	b	c	d \"
a=a,b=b,c=c,d=d \
input:"e	f	g	h"
a=e,b=f,c=g,d=h

$ ksh93 -c 'echo "  field3 field4  filed6" | { IFS="  " read a b c d e f g; echo "$d" ;}'
field4
$ zsh -c 'echo "  field3 field4  filed6" | { IFS="  " read a b c d e f g; echo "$d" ;}'
field4