# How to concatenate two (file) streams
**URL:** https://discourse.julialang.org/t/how-to-concatenate-two-file-streams/124082
**Category:** General Usage
**Created:** [December 22, 2024, 2:19am UTC](https://discourse.julialang.org/t/how-to-concatenate-two-file-streams/124082 "2024-12-22T02:19:00Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Abhro](https://discourse.julialang.org/u/Abhro)
#### Post date: [December 22, 2024, 2:19am UTC](https://discourse.julialang.org/t/how-to-concatenate-two-file-streams/124082/1 "2024-12-22T02:19:00Z")
How to create a stream which sequentially reads from multiple other streams? This is analogous to `cat` in unix, but for arbitrary streams. In python, something like this might be implemented as:
```python
def cat_streams(s1, s2):
for line in s1:
yield line
for line in s2:
yield line
```
(or some improved version thereof)
But I’m not sure what it would look like in Julia. I know there are task channels which yield, but this is more of a file imitation thing rather than an async thing.
---
### Author:  [@Yuan-Ru-Lin](https://discourse.julialang.org/u/Yuan-Ru-Lin)
#### Post date: [December 22, 2024, 6:37am UTC](https://discourse.julialang.org/t/how-to-concatenate-two-file-streams/124082/2 "2024-12-22T06:37:34Z")
With `file1` and `file2` set up as
```bash
$ echo "line1 in file1\nline2 in file1\nline3 in file1" > file1
$ echo "line1 in file2\nline2 in file2\nline3 in file2" > file2
$ cat file1 file2
line1 in file1
line2 in file1
line3 in file1
line1 in file2
line2 in file2
line3 in file2
```
you can use `Iterators.flatten` to concatenate two iterators given by `eachline`.
```julia-repl
julia> for line in Iterators.flatten([eachline("file1"), eachline("file2")])
println(line)
end
line1 in file1
line2 in file1
line3 in file1
line1 in file2
line2 in file2
line3 in file2
```