IFS read not working as nixCraft example

Question

I have a text file with tabs as separator:

a   1   956 9723
b   2   2   11432
c   3   1307    2964
c   4   2   12586
d   5   1377    11726
e   6   1735    8416
f   7   1320    10443
g   8   1175    9240
h   9   1598    9357
i   10  1405    2066

and I followed the example on nixCraft to extract the first column and last column:

while IFS="\t" read -r f1 f2 f3 f4
do
    echo "$f1"
    echo "$f4"
done < file.txt

It just returns the whole line. What went wrong?

System: CentOS 7, bash 4.2

@RakeshSharma thanks! I tried IFS=$"\t" 'cause I saw some post on SO using dollar sign before the separator, but it didn't work. However, you suggestion worked! Could you please explain more about the single/doube quote here? — leoce
– leoce, Commented Mar 25, 2017 at 10:31
The $'..' is a carryover from ksh onto bash' n some other shells, most notably, zsh. What it does is express escape sequences, e.g., \n \t etc. With double quotes, it's not special and IFS gets set to two chars backslash n a t and since you did not have a t in your input you didn't observer it's after effects. Try with IFS=$"\t" and some lines with "t" sprinkled in them.... — user218374
– user218374, Commented Mar 25, 2017 at 10:43
But to steer clear of shell anachronisms, use the method I ve detailed in the answer section below as it's completely shell agnostic (csh not included, ofc) — user218374
– user218374, Commented Mar 25, 2017 at 10:47

user218374user218374 · Accepted Answer · 2017-03-25 10:27:22Z

1

TAB=`echo 'x' | tr 'x' '\011'`; # tab
while IFS="$TAB" read -r f1 f2 f3 f4 junk; do
   printf '$f1=<%s>\n' "$f1"
   printf '$f4=<%s>\n' "$f4"
done

answered Mar 25, 2017 at 10:27

user218374

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