Bash script for parsing and processing specific lines of a text file - bash

Question

I have the following text file
40 timesteps took 58.320842 seconds
greetings 0
80 timesteps took 58.048400 seconds
greetings 0
120 timesteps took 59.459687 seconds
greetings 0
What I would like to do is parse only the lines containing the seconds, add them together and print out the final result.
How can I do that?
Thank you in advance.

Answer 1

awk is well suited for this type of processing.
To deal with floating point precision, you can use printf with a format-string for each variable involved.
There is also another way which sets the format-string for all evaluated variables. The formatting is applied during evaluations (which internally use sprintf. The controlling built-in variable is OFMT. See Built-in Variables That Control awk.
#!/bin/bash
file="$1" # $1 is the 1st command line parameter
awk -vOFMT="%.6f" '/ took /{ secs+=$4 } END{ print secs }' "$file"
Using sed is more involved, because it cannot do any calculations and even bash itself cannot do floating point arithmetic, so you need to use something like awk or bc in any case.
If you really want to use sed:
#!/bin/bash
file="$1" # $1 is the 1st command line parameter
{ sed -nr 's/.* took ([0-9.]+).*/\1+/p' "$file" |tr -d '\n'; echo 0; } |bc

Answer 2

You can use a simple shell command:
grep timesteps <file-name> | awk '{x += $4} END{printf("%.5f", x)}'
Change the number in the printf statement to your preferred output precision.

Answer 3

The awk solutions are good answers. For fun, here is a Ruby answer...
ruby -e 'puts readlines.inject(0) { |m, v| m += v.split[3].to_f }' < file
...or perhaps...
ruby -e 'puts readlines.map { |x| x.split[3].to_f }.reduce(&:+)' < file
...to pass the file as a parameter to a script...
#!/usr/bin/ruby
puts $<.map { |x| x.split[3].to_f }.reduce(&:+)