strings are missing after concatenating two or more variable string in bash

Question

When I am running two while loop and trying to concatenating two variable strings (from two loops), the final output (string) is weird. I have tried different way to concatenating but did not get the answer: Below is the code: [I need vfile="var1_Amon_My_model1*.nc"]

#!/bin/bash
jcount=1
extn="*.nc"
while read line
do
mname=$line
echo " Working on model - " $mname
echo " and model number = "$jcount
while read line
do
vname=$line
vfile="${vname}""_Anom_""${mname}""${extn}"
echo $vfile
done<varlists.txt
echo "******************************************"
jcount=$((jcount+1))
done<model_test1.txt

In varlists.txt

var1
var2

In model_test1.txt

My_model1
My_model2

After executing the script, it is showing

 Working on model -  My_model1
 and model number = 1
*.ncm_My_model1
*.ncm_My_model1
******************************************

Answer 1

Your text files have Windows/DOS CRLF line endings.

The strings are concatenating correctly, but the carriage return byte is left at the end of vname and mname, because it's not part of a line ending on Unix and so wasn't used up by read. When you print the string out, the display is mangled instead. Carriage returns shift the cursor back to the start of the line (like a typewriter), letting text be overwritten.

When you print some text with a carriage return in it, the text up to the CR appears as normal, then the output cursor moves back to the start, and then later parts of the string are being printed over the top of earlier parts. That's why the "*.nc" appears at the start of the line in your reported output even though "${extn}" is last - mname ends with a carriage return.

You can run your text files through dos2unix to remove the extra carriage return bytes. You could also use ${vname%$'\r'} in the script to truncate trailing CRs if you don't want to or can't modify the files.