Archive for the 'linux' Category

One simple way to do simple floating point arithmetics in shell

set n = 128
set beta = `echo "(-0.6)*($n)*($n)" | bc -l`
set ppn = 16
set np = 31
set nodes = `echo "if ($np%$ppn==0) {$np/$ppn;} else {$np/$ppn+1}" | bc`


Useful Linux command—paste

I have for long ignored blogging, but today I came across the useful linux command “paste” and I thought I should write it down. In the past I have used quite a few smart tricks to handle data or output files, but I failed to document these tricks. I really should do it this time.

So here is the story. I have an output file test.o1551739 which contains lines such as “iter = 125” scattering everywhere. I need to get the sum of all the numbers in these lines. How can I achieve this without writing a program? The following is a little thought process.

First, I am so used to grep that I can grab all such lines by doing:

grep iter test.o1551739

Then, use sed to get rid of the suffix “iter = “:

sed s/"iter = "//

Now that I have a bunch of numbers, one in a line. How can I sum them up? Yah, here comes the usage of paste. The command paste allows me to merge the lines and put a delimiter in between. I chose to use the plus sign, because then it gives me an arithmetic expression. Try this:

paste -sd+

Once I have the arithmetic expression, I’ll just use bc to calculate the result. So piping all these steps, here is the one line command:

grep iter test.o1551739 | sed s/"iter = "// | paste -sd+ | bc

Nice. I realize that there must be tons of ways to do the same job. But I really love my solution.


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