AWK - Unable to update the files - bash

Question

I have 300 txt files in my directory in the following format
regional_vol_WM_atlas[1-300].txt
651328 651328
553949 553949
307287 307287
2558 2558
The following awk script was supposed to create a new file by performing calculation on fourth row of each existing files in my directory .
#!/bin/bash
awk=/usr/bin/awk
awkcommand='
FNR == 1 {
newfilename = FILENAME ; sub(".txt", "_prop.txt", newfilename)
printf "" > newf
ilename
}
FNR == 4 {
$1=($1/0.824198)*0.8490061
$2=($2/0.824198)*0.8490061
}
{
print >> newfilename
}
'regional_vol_WM_atlas[0-9].txt regional_vol_WM_atlas[0-9][0-9].txt regional_vol_WM_atlas1[0-4][0-9].txt regional_vol_WM_atlas15[02].txt
Unfortunately i could not update any file in the directory ,when i run the file, i am incurring following error
dev#dev-OptiPlex-780:/media/dev/Daten/Task1/subject1/t1$ '/media/dev/Daten/Task1/subject1/t1/Method'
/media/dev/Daten/Task1/subject1/t1/Method: line 18: regional_vol_WM_atlas10.txt: command not found
Could you please correct me where i am wrong

Answer 1

Your script is not calling awk. It defines a variable named awk and then tries to execute the file regional_vol_WM_atlas10.txt with the variable awkcommand set in its environment. Alas, that file is not in your PATH, so bash cannot find it. You need to instead do:
awk "$awkcommand" file1 file2 ...
(where file1, file2, etc. are the input files you want to use as input.)
Also, note that your current script is appending the literal text regional_vol_WM_atlas[0-9].txt to the end of the awk command (or if a file exists which matches that glob, the name of that file is being appended), which you do not want. Overall, what you were trying to do should have been written:
#!/bin/bash
awkcommand='
FNR == 1 {
newfilename = FILENAME ; sub(".txt", "_prop.txt", newfilename)
printf "" > newfilename
}
FNR == 4 {
$1=($1/0.824198)*0.8490061
$2=($2/0.824198)*0.8490061
}
{
print >> newfilename
}
'
awk "$awkcommand" regional_vol_WM_atlas[0-9].txt \
regional_vol_WM_atlas[0-9][0-9].txt \
regional_vol_WM_atlas1[0-4][0-9].txt \
regional_vol_WM_atlas15[02].txt

Answer 2

The problem is that a variable can be assigned for a command, for example:
x='hello' some_command
Which in effect is what bash thinks you are trying to do. The culprit is the whitespace, which acts as a command separator, so just escape (prefix with a \) the whitespace in the list of filenames:
#!/bin/bash
awk=/usr/bin/awk
awkcommand='
FNR == 1 {
newfilename = FILENAME ; sub(".txt", "_prop.txt", newfilename)
printf "" > newf
ilename
}
FNR == 4 {
$1=($1/0.824198)*0.8490061
$2=($2/0.824198)*0.8490061
}
{
print >> newfilename
}
'\ regional_vol_WM_atlas[0-9].txt\ regional_vol_WM_atlas[0-9][0-9].txt\ regional_vol_WM_atlas1[0-4][0-9].txt\ regional_vol_WM_atlas15[02].txt
The only thing I have altered is the final line.