command out to a variable

zebrafx · 02-19-2009, 05:28 PM

Hopefully this wasn't asked like a million times, tried searching but haven't found the right solution. I generally want to output a number from a linux command into a variable. Basically it would generate a couple lines of text and then on the last line output:

tcp: 0 bytes in 0.00 real seconds = 3242.00 KB/sec +++

I want to get that 3242.00 value into a variable. It going to be a script that basically will like add up 20 of them and give the average.

Thanks for reading this message.

Edit: I forgot to mention I am using shell script.

colucix · 02-19-2009, 05:35 PM

The shell does not manage floating point numbers, hence you have to use some external commands like bc or awk. Here is a simple awk solution:

Code:

awk '{sum+=$9;count++}END{print sum/count}' file

this requires the input is always formatted as in your example, that is the requested number is the ninth field in each line of the file.

zebrafx · 02-19-2009, 06:08 PM

Quote:

Originally Posted by colucix

The shell does not manage floating point numbers, hence you have to use some external commands like bc or awk. Here is a simple awk solution:

Code:

awk '{sum+=$9;count++}END{print sum/count}' file

this requires the input is always formatted as in your example, that is the requested number is the ninth field in each line of the file.

I am not sure how to use awk. I looked up awk and had trouble finding examples to my situation so I am not sure on the syntaxing.

Basically I was using prior:
/usr/local/bin/istcp -t $iprec -p 20000 | grep KB/sec

and it outputs:
tcp: 0 bytes in 0.00 real seconds = 0.00 KB/sec +++

I tried the code below and

Code:

/usr/local/bin/istcp -t $iprec -p 20000 | awk {sum+=$9;count++}END{print sum/count}

I get an error below.
./tcptest: line 12: unexpected EOF while looking for matching `''
./tcptest: line 17: syntax error: unexpected end of file

colucix · 02-20-2009, 12:27 AM

Well, the error is due to the fact you missed the single quotes around the awk program. Look at my previous post: single quotes are mandatory.

Anyway, I misinterpreted your first post, since you talk about calculating the mean of 20 numbers, so I thought you had a file with 20 lines. My awk command line calculates the mean of the number in the ninth field of each line.

From your last example, I think you want help just for the first part of your issue, that is to store the number in a shell variable. To do this use command substitution:

Code:

var=$(command)

which assigns the output of the command to the variable. To extract the number from the line, again you can use awk or eventually the command cut. For example:

Code:

var=$(/usr/local/bin/istcp -t $iprec -p 20000 | grep KB/sec | awk '{print $9}')

zebrafx · 02-20-2009, 09:12 AM

Quote:

Originally Posted by colucix

Well, the error is due to the fact you missed the single quotes around the awk program. Look at my previous post: single quotes are mandatory.

Anyway, I misinterpreted your first post, since you talk about calculating the mean of 20 numbers, so I thought you had a file with 20 lines. My awk command line calculates the mean of the number in the ninth field of each line.

From your last example, I think you want help just for the first part of your issue, that is to store the number in a shell variable. To do this use command substitution:

Code:

var=$(command)

which assigns the output of the command to the variable. To extract the number from the line, again you can use awk or eventually the command cut. For example:

Code:

var=$(/usr/local/bin/istcp -t $iprec -p 20000 | grep KB/sec | awk '{print $9}')

Ah perfect. Ok, I was messing around a bit with awk and I had something close to what you posted. It didn't work though lol. Thanks for the help, I now understand how to use it.