# How to concatenate multiple \`.gz\` files within Julia?
**URL:** https://discourse.julialang.org/t/how-to-concatenate-multiple-gz-files-within-julia/44975
**Category:** General Usage
**Tags:** question
**Created:** [August 15, 2020, 4:08am UTC](https://discourse.julialang.org/t/how-to-concatenate-multiple-gz-files-within-julia/44975 "2020-08-15T04:08:48Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@biona001](https://discourse.julialang.org/u/biona001)
#### Post date: [August 15, 2020, 4:08am UTC](https://discourse.julialang.org/t/how-to-concatenate-multiple-gz-files-within-julia/44975/1 "2020-08-15T04:08:48Z")
I want to combine multiple `.gz` files into 1 within Julia. The command to do so in the command line is:
```julia
cat file1.gz file2.gz file3.gz > allfiles.gz
```
But the following does not work:
```julia
files = ["file1.gz", "file2.gz", "file3.gz"]
run(pipeline(`cat $files`, stdout="allfiles.gz"))
```
The function doesn’t throw any error but `allfiles.gz` is corrupt. Is this a bug?
---
### Author:  [@biona001](https://discourse.julialang.org/u/biona001)
#### Post date: [August 15, 2020, 4:30am UTC](https://discourse.julialang.org/t/how-to-concatenate-multiple-gz-files-within-julia/44975/2 "2020-08-15T04:30:29Z")
I figured it out as I was trying make a MWE. The following does not work:
```julia
using CodecZlib
for i in 1:3
file = "file$i.gz"
x = rand(2, 2)
io = GzipCompressorStream(open(file, "w"))
write(io, "hello, testing from i = $i")
end
files = ["file1.gz", "file2.gz", "file3.gz"]
# runs without error but file corrupted
run(pipeline(`cat $files`, stdout="allfiles.gz"))
```
But this works:
```julia
using CodecZlib
for i in 1:3
file = "file$i.gz"
x = rand(2, 2)
io = GzipCompressorStream(open(file, "w"))
write(io, "hello, testing from i = $i")
close(io) #need to close stream
end
files = ["file1.gz", "file2.gz", "file3.gz"]
run(pipeline(`cat $files`, stdout="allfiles.gz")) # works
```
The difference is that in the first case I forgot the close the stream. Sorry!
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [August 15, 2020, 8:18am UTC](https://discourse.julialang.org/t/how-to-concatenate-multiple-gz-files-within-julia/44975/3 "2020-08-15T08:18:26Z")
Note that your problem is simply concatenating files, and has nothing specific to gz (you are simply concatenating compressed files _without_ compressing/decompressing, which is fine, you can do it with gz).
So you would simply read and write them, eg
```julia
open("allfiles.gz", write = true) do io # UNTESTED, just a sketch
for file in ["file1.gz", "file2.gz", "file3.gz"]
write(io, read(file, String))
end
end
```
or do some variant of block based IO when the files are larger.