read float from a specific line in a file using shell script

Question

I have a series of data files that I need to get a few specific values from. I know the line in the file that the data is on. My data files look like this

x    y    z
1    0.2  0.3
2    0.1  0.2
3    0.5  0.6
etc.

I am using a shell script to access the files, collect the desired data from each file, and output the collected data in one file.

For example, I need the y value in line 3, 0.1. I have tried the following

let dataLine=3
let yVal=`head -n $dataLine dataFile | tail -n 1 | awk '{print $2}'`

but I get the following error

let: yVal=0.1: syntax error: invalid arithmetic operator (error token is ".1")

I have tried adding | bc | bc after awk '{print $2}' but then it did not even register the correct value for what should be assigned to yVal . When I do it as shown above, it does show that it is recognizing the value in the correct line and column.

Thanks for the help,

Answer 1

If you want to get 3rd line's 2nd field then following may help you in same.

Solution 1st: If you want to pass any shell variable's value to any awk variable then following may help you in same.

line_number=3
awk -v line="$line_number" 'FNR==line{print $2}'  Input_file

Solution 2nd: If you want to directly print 3rd line's 2nd field then following may help you in same.

awk 'FNR==3{print $2}'  Input_file

Answer 2

$ dataLine=3
$ yVal=$(awk -v dataLine="$dataLine" 'NR==dataLine{print $2}' data)
$ echo $yVal
0.1