How can I adjust nth number in a line?

Question

File contents:

RANDOM TEXT    num1=400    num2=15    RANDOM TEXT
RANDOM TEXT    num1=300    num2=10    RANDOM TEXT
RANDOM TEXT    num1=200    num2=5    RANDOM TEXT

I would like to subtract 5 for each num2 per line like so:

RANDOM TEXT    num1=400    num2=10    RANDOM TEXT
RANDOM TEXT    num1=300    num2=5    RANDOM TEXT
RANDOM TEXT    num1=200    num2=0    RANDOM TEXT

Pure bash is preferred, but no biggie if another GNU tool does it better.

Answer 1

Using awk:

awk '{ for (i=1;i<=NF;i++) { if ($i ~ /num2=/) {sub(/num2=/, "", $i); $i="num2="$i-5; print} } }' file

This will loop through each column of each line looking for the column that contains num2=. When it finds that column it will:

1. Remove num2= - sub(/num2=/, "", $i)
2. Redefine that column as num2={oldnum-5} - $i="num2="$i-5
3. Print the line - print

Answer 2

perl:

perl -pe 's/(?<=num2=)(\d+)/$1 - 5/e' file

To store the contents back into the file:

perl -i -pe ...

Answer 3

[Just because I'm trying to become more familiar with Miller - it requires some jumping through hoops to get the heterogeneous output]:

$ mlr --fs ' ' --repifs --ocsvlite --headerless-csv-output put '
    $num1 = "num1=".$num1; $num2 = "num2=".($num2-5)
' file
RANDOM TEXT num1=400 num2=10 RANDOM TEXT
RANDOM TEXT num1=300 num2=5 RANDOM TEXT
RANDOM TEXT num1=200 num2=0 RANDOM TEXT

If the input is actually TSV in which some columns may contain spaces, then

$ mlr --fs '\t' --ocsvlite --headerless-csv-output put '
    $num1 = "num1=".$num1; $num2 = "num2=".($num2-5)
' file
RANDOM TEXT num1=400    num2=10 RANDOM TEXT
RANDOM TEXT num1=300    num2=5  RANDOM TEXT
RANDOM TEXT num1=200    num2=0  RANDOM TEXT

Answer 4

Using Vim:

vim +'g/^/exe "norm! 3Wf=5\<C-A>"' +wq file

The first + argument runs a series of normal mode operations on each line to increment the number 5 times. It uses a :global command to run this on every line. Simply using :normal with a range %norm would be simpler if we weren't using CTRLA to increment the number, but in order to (easily) pass this control character into Vim we build the command as a string to run with :execute, and thus we need the :global.

The second + argument simply saves the file.

If the format of RANDOM TEXT is less regular (or if you just prefer regular expressions), you could instead use a :substitute command:

vim +'%s/num2=\zs\d\+/\=submatch(0) + 5' +wq file

This uses a :substitute command to replace the N part of num2=N with the existing value plus five.