Question

I have a configuration file that has variables and value separate by spaces. I want to take the value (in the second column) of certain matches and inline edit the file, dividing this match by 2. I also would like to preserve spacing and use a ceiling function on the value.

For example, the file:
To recap, using an actual example file, if my file was:

OTHER TEXT 1
OTHER TEXT 2
restartfreq        325
dcdfreq            325
xstFreq            325
outputEnergies     325
outputPressure     325
OTHER TEXT 3

Would become:

OTHER TEXT 1
OTHER TEXT 2
restartfreq        163
dcdfreq            163
xstFreq            163
outputEnergies     163
outputPressure     163
OTHER TEXT 3

I would prefer to do this all in a Bash script using Linux commands. I’ve considered switching to a small c++ program, but for now am sticking with a scripted tool-based solution.

Working towards this, I posted this inquiry last week:
How Can I Mix Math with Regex's in Awk or Sed?

I came eventually to a long-winded solution, but ghostdog74 proposed this more eloquent solution:

awk '$1=="restartfreq"{$2=$2/2;}1' file > t && mv t file

This does what I want… almost.

As I said, I also need to implement a ceiling function, and preferably preserve white space — and I’d like to make it capable of dividing the values of multiple matches, not just one.

Can I do this in a one-liner or small nested awk script? Any tips??

---

Solution:

I’ve taken Ghostdog’s answer:

awk '$1~/[fF]req|output/{ n=$2/2; sub(/ [0-9][0-9]*$/,n)}1' file

And modified it slightly to allow comments on the end of the line and to perform the ceiling as per my request. I’m going to ask a separate function about how to use short functions in awk one liners.

awk '$1~/restartfreq|dcdfreq|xstFreq|outputEnergies|outputPressure/{ a=$2/2; n= (a== int(a)) ? a : int(a)+1; sub(/ [0-9][0-9]*.*$/,n)}1' file > temp && mv -f temp file

Good work Ghostdog!

Answer 1

$ awk '$1~/[fF]req|output/{ n=$2/2; sub(/ [0-9][0-9]*$/,n)}1' file
OTHER TEXT 1
OTHER TEXT 2
restartfreq       162.5
dcdfreq           162.5
xstFreq           162.5
outputEnergies    162.5
outputPressure    162.5
OTHER TEXT 3