How to find and extract a numeric value from a text file?

I have a file called "RFEM_Information.txt" which has 13 lines.

[None]======================================================================
        <Drainage>DrainedUndrained</Drainage>
        <Scr>0</Scr>
        <UseCavitationCutOff>No</UseCavitationCutOff>
        <pt>100</pt>
        <E>30</E>
        <Nu>0.25</Nu>
        <K>20</K>
[None]======================================================================
[Log][None]No OF NODES     = 474
[Log][None]
[Log][None]BEST STSR = 1.528
[Log] [None]=================================================================

I want to find line 12 (in general the line number is unknown) which has "[Log][None]BEST STSR = 1.528" and I want to extract the number or all the information of the line after "=" (I want to return as a number 1.528).

How can I find the relevant line and read the value from it?

Try using Fortran index function to scan the line for "BEST STSR" substring, then extract the number.

Here is an example:

program main
    implicit none
    character(128) :: line
    integer :: i, stat, unit
    real :: val
    
    open (FILE="data.txt", NEWUNIT=unit, STATUS="old", ACTION="read", IOSTAT=stat)
    if (stat /= 0) error stop "Cannot open file"
      
    do while (.true.)
        read (unit, "(a)", IOSTAT=stat) line
        if (stat /= 0) exit

        ! Scan buffer for keyword "BEST STSR". Extract number if keyword is found.
        i = index(line, "BEST STSR")
        if (i /= 0) then
            ! length("BEST STSR =") = 11
            read (line(i+11:), *, IOSTAT=stat) val
            if (stat /= 0) error stop "Cannot read value"

        end if
    end do
      
    close (unit)
    
end program main