Grep A Column Based On Column Name Post: 302981239

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Top Forums UNIX for Beginners Questions & Answers Grep A Column Based On Column Name Post 302981239 by Don Cragun on Thursday 8th of September 2016 06:07:03 PM

09-08-2016

Registered User

Quote:

Originally Posted by jimmyf

I got it to work!!!

Code:

awk -v header="Dog" '
BEGIN { FS=" "; c=0 }
NR == 1 { for (i=1;i<=NF;i++) { if ($i==header) { c=i }} }
NR > 1 && c>0 { print $c }
' dogs.log

vbe, I think it was the fear of the universe when you questioned me. Thanks!

Congratulations. Well done.

Here is a shell script that incorporates your awk code and an alternative that might help with issues you might run into in future endeavors.

If you save the following script in a file named tester:

Code:

#!/bin/ksh
echo 'Original code results:'
awk -v header="${1:-Dog}" '
BEGIN { FS=" "; c=0 }
NR == 1 { for (i=1;i<=NF;i++) { if ($i==header) { c=i }} }
NR > 1 && c>0 { print $c }
' dogs.log
echo "*** Exit status: $?"

printf '\nModified code results:\n'
awk -v header="${1:-Dog}" '
NR == 1 {
	for(i = 1; i <= NF; i++)
		if($i == header) {
			c = i
			next
		}
	printf("Header \"%s\" not found.\n", header)
	exit 1
}
{	print $c
}' dogs.log
echo "*** Exit status: $?"

and make it executable with:

Code:

chmod +x tester

and invoke it with no arguments:

Code:

./tester

you get:

Code:

Original code results:
fido
dopey
ears
barky
*** Exit status: 0

Modified code results:
fido
dopey
ears
barky
*** Exit status: 0

If you invoke it with an argument that is the name of one of the headings in dogs.log, for example:

Code:

./tester Cat

Code:

Original code results:
sneaky
poptart
whisker
herd
*** Exit status: 0

Modified code results:
sneaky
poptart
whisker
herd
*** Exit status: 0

And if you invoke it with an argument that does not match any of the header line values, for example:

Code:

./tester Horse

you get:

Code:

Original code results:
*** Exit status: 0

Modified code results:
Header "Horse" not found.
*** Exit status: 1

This was written and tested using a Korn shell, but will work with any shell that performs the basic parameter expansions required by the POSIX standards (such as ash, bash, dash, ksh, and zsh).

Don Cragun

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