Process multiple files and append them in linux/unix - linux

Question

I have over 100 files with at least 5-8 columns (tab-separated) in each file. I need to extract first three columns from each file and add fourth column with some predefined text and append them.
Let's say I have 3 files: file001.txt, file002.txt, file003.txt.
file001.txt:
chr1 1 2 15
chr2 3 4 17
file002.txt:
chr1 1 2 15
chr2 3 4 17
file003.txt:
chr1 1 2 15
chr2 3 4 17
combined_file.txt:
chr1 1 2 f1
chr2 3 4 f1
chr1 1 2 f2
chr2 3 4 f2
chr1 1 2 f3
chr2 3 4 f3
For simplicity I kept file contents same.
My script is as follows:
#!/bin/bash
for i in {1..3}; do
j=$(printf '%03d' $i)
awk 'BEGIN { OFS="\t"}; {print $1,$2,$3}' file${j}.txt | awk -v k="$j" 'BEGIN {print $0"\t$k”}' | cat >> combined_file.txt
done
But the script is giving the following errors:
awk: non-terminated string $k”}... at source line 1
context is
<<<
awk: giving up
source line number 2
awk: non-terminated string $k”}... at source line 1
context is
<<<
awk: giving up
source line number 2
Can some one help me to figure it out?

Answer 1

You don't need two different awk scripts. And you don't use $ to refer to variables in awk, that's used to refer to input fields (i.e. $k means access the field whose number is in the variable k).
for i in {1..3}; do
j=$(printf '%03d' $i)
awk -v k="$j" -v OFS='\t' '{print $1, $2, $3, k}' file$j.txt
done > combined_file.txt

Answer 2

As pointed out in the comments your problem is youre trying to use odd characters as if they were double quotes. Once you fix that though, you don't need a loop or any of that other complexity all you need is:
$ awk 'BEGIN{FS=OFS="\t"} {$NF="f"ARGIND} 1' file*
chr1 1 2 f1
chr2 3 4 f1
chr1 1 2 f2
chr2 3 4 f2
chr1 1 2 f3
chr2 3 4 f3
The above used GNU awk for ARGIND.