Bash: Use for loop to iterate over file without using cat

Introduction:

In this very brief post I just wanted to demonstrate a way to use the for loop to iterate over a file without using the cat command.

Here is a file containing 10 numbers, 1 number on each line.

cat seq.txt
1
2
3
4
5
6
7
8
9
10

If I wanted to loop over it using for loop in bash I could type:

for i in `cat seq.txt`; do echo $i ;done

But what if I don't want to read in the file using cat command?

I could use input redirection to read in the file contents as shown in the below example:

for i in $(<seq.txt); do echo $i ; done

1

2

3

4

5

6

7

8

9

10

                            

One more way of avoiding the cat command would be to read the file into an array and then loop over the array as shown below.

readarray -t ARR < seq.txt

for i in "${ARR[@]}"; do echo $i; done

1

2

3

4

5

6

7

8

9

10

Conclusion

There is nothing wrong with using the cat command to read in file contents while iterating over it in a for loop. I just found redirecting directly from STDIN to be more elegant and I would try to use it more often.