BASH: Iterating two v ariables in a for loop - bash

Question

I am having two files numbers.txt(1 \n 2 \n 3 \n 4 \n 5 \n) and alpha.txt (a \n n \n c \n d \n e \n)
Now I want to iterate both the files at the same time something like.
for num in `cat numbers.txt` && alpha in `cat alpha.txt`
do
echo $num "blah" $alpha
done
Or other idea I was having is
for num in `cat numbers.txt`
do
for alpha in `cat alpha.txt`
do
echo $num 'and' $alpha
break
done
done
but this kind of code always take the first value of $alpha.
I hope my problem is clear enough.
Thanks in advance.
Here it is what I actually intended to do. (Its just an example)
I am having one more file say template.txt having content.
variable1= NUMBER
variable2= ALPHA
I wanted to take the output from two files i.e numbers.txt and alpha.txt(one line from both at a time) and want to replace the NUMBER and ALPHA with the respective content from those two files.
so here it what I did as i got to know how to iterate both files together.
paste number.txt alpha.txt | while read num alpha
do
cp template.txt temp.txt
sed -i "{s/NUMBER/$num/g}" temp.txt
sed -i "{s/ALPHA/$alpha/g}" temp.txt
cat temp.txt >> final.txt
done
Now what i am having in final.txt is:
variable1= 1
variable2= a
variable1= 2
variable2= b
variable1= 3
variable2= c
variable1= 4
variable2= d
variable1= 5
variable2= e
variable1= 6
variable2= f
variable1= 7
variable2= g
variable1= 8
variable2= h
variable1= 9
variable2= i
variable1= 10
variable2= j
Its very simple and stupid approach. I wanted to know is there any other way to do this??
Any suggestion will be appreciated.

Answer 1

No, your question isn't clear enough. Specifically, the way you wish to iterate through your files is unclear, but assuming you want to have an output such as:
1 blah a
2 blah b
3 blah c
4 blah d
5 blah e
you can use the paste utility, like this:
paste number.txt alpha.txt | while read alpha num ; do
echo "$num and $alpha"
done
or even:
paste -d# alpha num | sed 's/#/ blah /'

Answer 2

Your first loop is impossible in bash. Your second one, without the break, would combine each line from numbers.txt with each line from alpha.txt, like this:
1 AND a
1 AND n
1 AND c
...
2 AND a
...
3 AND a
...
4 AND a
...
Your break makes it skip all lines from the alpha.txt, except the 1st one (bmk has already explained it in his answer)
It should be possible to organize the correct loop using the while loop construction, but it would be rather ugly.
There're lots of easier alternatives which maybe a better choice, depending on specifics of your task. For example, you could try this:
paste numbers.txt alpha.txt
or, if you really want your "AND"s, then, something like this:
paste numbers.txt alpha.txt | sed 's/\t/ AND /'
And if your numbers are really sequential (and you can live without 'AND'), you can simply do:
cat -n alpha.txt

Answer 3

Here is an alternate solution according to the first model you suggested:
while read -u 5 a && read -u 6 b
do
echo $a $b
done 5<numbers.txt 6<alpha.txt
The notation 5<numbers.txt tells the shell to open numbers.txt using file descriptor 5. read -u 5 a means read from a value for a from file descriptor 5, which has been associated with numbers.txt.
The advantage of this approach over paste is that it gives you fine-grain control over how you merge the two files. For example you could read one line from the first file and twice from the second file.

Answer 4

In your second example the inner loop is executed only once because of the break. It will simply jump out of the loop, i.e. you will always only get the first element of alpha.txt. Therefore I think you should remove it:
for num in `cat numbers.txt`
do
for alpha in `cat alpha.txt`
do
echo $num 'and' $alpha
done
done

Answer 5

If multiple loop isn't specifically your requirement but getting corresponding lines is then you may try the following code:
for line in `cat numbers.txt`
do
echo $line "and" $(cat alpha.txt| head -n$line | tail -n1 )
done
The head gets you the number of lines equal to the value of line and tail gets you the last element.

Answer 6

#tollboy, I think the answer you are looking for is this:
count=1
for item in $(paste number.txt alpha.txt); do
if [[ "${item}" =~ [a-zA-Z] ]]; then
echo "variable${count}= ${item}" >> final.txt
elif [[ "${item}" =~ [0-9] ]]; then
echo "variable${count}= ${item}" >> final.txt
fi
count=$((count+1))
done
When you type paste number.txt alpha.txt in your console, you see:
1 a
2 b
3 c
4 d
5 e
6 f
7 g
8 h
9 i
10 j
From bash's point of view $(paste number.txt alpha.txt) it looks like this:
1 a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 9 i 10 j
So for each item in that list, figure out if it is alpha or numeric, and print it to the output file.
Lastly, increment the count.