Understanding awk 'expansion'

Shell Programming and Scripting
1

Heyas

Recently i wanted to help someone with an awk script, but the end-script didnt work as expected.

He wanted, if HOME was empty, to get the HOME of the current USER from /etc/passwd.
At first i tried hardcoded with root:

awk -F: '/^root/ {print $6}' /etc/passwd

As that worked, i've added a variable, for the changeable 'current user'.

awk -v U=$(whoami) -F: '/^U/ {print $6}' /etc/passwd

But this didnt want to work, so in the end i had to:

cmd="awk -F:  '/^$(whoami)/ {print \$6}' /etc/passwd"
eval $cmd

Why is my 2nd code not working? (just returns empty)
Any (better) ideas?

Thank you

2

As /.../ is a regex constant, it would try to match the literal string "U" at the begin-of-line. Try $0 ~ "^"U .

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3 
awk -v U=$(whoami) -F: '"/^" U "/" {print $6}' /etc/passwd
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5

Hello sea,

Following may also be an option on same.

awk -v U=$(whoami) -F: '($1 == U) {print $6}' /etc/passwd

Actually in my server directories are having pretty similar names as users have so I have done with by directly comparing the 1st column itself.

Thanks,
R. Singh

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6

Hi, I do not think this will work. That evaluates to:

awk -F: '"/^username/"{print $6}' /etc/passwd

Which means if the string "/^username/" is true (i.e. non-empty) then print $6

So this always evaluates to true and it will print field 6 on every line..