Awk - how to print variable with string

Question

I have this input and I would like to learn how to save string after = to variable and use it for output filename and in the first line of output that will start with \"#\"

Answer 1

Untested code follows:

/^c/ { X[$2] = $3 }
/^c end/ { outfile = X["column2="] X["ROIysiz="] X["column3="]
           print "#", X["column2="], X["RedNumDa="] > outfile }
!/^c/ { print $0 >> outfile }

EDIT: The code is now tested:

$ cat x
c ROIysiz= 28
c column1= HJD
c RedNumDa= 18262
c column3= ERROR
c column2= FLUX
c end header ---------------------------------------------------------------------------------------
2.458375368952875026e+06 -8.420548421860798386e-04 7.020812100561693928e-03
2.458375579737625085e+06 -5.579159672996818198e-03 1.285380720081348528e-03
2.458376278315599542e+06 -7.634101850411220518e-03 2.481065693991901019e-03
2.458376347386624664e+06 7.223482191697593166e-04 2.319993894372075760e-03
2.458376416108166799e+06 5.238757879614985152e-03 1.389030320490110878e-03
2.458376485913363751e+06 6.777606553373448882e-03 8.887787066666734273e-04
2.458377048675692175e+06 1.950435173388009522e-02 3.242344477396308117e-03
2.458377185153110884e+06 1.885754079806525874e-02 2.090836971653367571e-03
$ awk '
/^c/ { X[$2] = $3 }
/^c end/ { outfile = X["column2="] X["ROIysiz="] X["column3="]
           print "#", X["column2="], X["RedNumDa="] > outfile }
!/^c/ { print $0 >> outfile }
' x
$ cat FLUX28ERROR
# FLUX 18262
2.458375368952875026e+06 -8.420548421860798386e-04 7.020812100561693928e-03
2.458375579737625085e+06 -5.579159672996818198e-03 1.285380720081348528e-03
2.458376278315599542e+06 -7.634101850411220518e-03 2.481065693991901019e-03
2.458376347386624664e+06 7.223482191697593166e-04 2.319993894372075760e-03
2.458376416108166799e+06 5.238757879614985152e-03 1.389030320490110878e-03
2.458376485913363751e+06 6.777606553373448882e-03 8.887787066666734273e-04
2.458377048675692175e+06 1.950435173388009522e-02 3.242344477396308117e-03
2.458377185153110884e+06 1.885754079806525874e-02 2.090836971653367571e-03

The first line, in the /^c/ pattern, saves each header line (the lines that begin with the letter c). The second and third lines, in the /^c end/ pattern, compute the output filename using string concatenation to join the various header values, then writes the first line of the output file in a similar manner, using the , operator to separate fields. The fourth line, in the !/^c/ pattern, prints each non-header line, unchanged, to the output file. Associative array X stores each header key as its index and the associated value at its value.