Find maximum value on only specific lines bash script-CodePudding

I have the following text :

title
P1 : I = -20.32;
P2 : I = 24.07;
P3 : I = -16.68;
T_B1 : I = 24.93;
T_H1 : I = -7.49;
T_B2 : I = 25.48;
T_H2 : I = -0.20;
T_B3 : I = 25.81;
T_H3 : I = 5.32;
T_B4 : I = 26.00;
T_H4 : I = 9.27;
T_B5 : I = 26.09;
T_H5 : I = 11.84;
T_B5 : I = 26.11;
T_H5 : I = 11.04;

And I just would like the maximum value of T_H*

T_H5 : I = 11.84;

I tried something like this :

sort -t= -nr -k3 text | head -1

I don't understand if I have to use sort or awk because I only want to sort on specifis lines. I tried to google it many times and read the sort command manual but I don't get what I want. If somebody could help me this this it would be cool :) Thank you

CodePudding user response：

If you want to solve this using UNIX tools, then you should use a UNIX approach of one tool for each purpose.

grep '^T_H' < input | # Filter
    sort -t= -nr -k3 | # sort
    head -n1

Of course there are other ways to solve it with fewer pipes, but that doesn't seem to be what you're after.

CodePudding user response：

Both will work, but Awk can be quite a bit more efficient and succinct.

awk '/^T_H[0-9]/ { x = 0   substr($1, 4)
    if (maxx < x) maxx = x }
  END { print 0 maxx }' text

The main body extracts the integer after T_H and remerbers the current max. The 0 forces conversion to a number, which also discards any nonnumeric suffix. The 0 inthe END block similarly supplies a numeric context, so that the output will be a number rather than an empty strin, if maxx is empty for some reason.

If you mean the max of the last field rather than the number immediately after T_H, that's even easier; just use $NF instead of the substr(...)expression.

If you want to print the whole line, keep that in a second variable, and update it whenever you update the max.

awk '/^T_H[0-9]/ { x = 0   $NF
    if (maxx < x) { res = $0; maxx = x } }
  END { print res }' text

(This also illustrates the $NF variation.)

CodePudding user response：

Another awk script, to get the maximum value of T_H*:

awk '/^T_H/{max=($5 0>max?$5 0:max)}END{print max}' file
11.84

The $5 0 allows to strip out the ; to only get the value.
This value is compared to the max variable in the ternary operator.
When end of the file is reached, the max value is printed.