# How to create MD5 file within add\_custom\_target
**URL:** https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156
**Category:** Usage
**Created:** [March 4, 2022, 8:27am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156 "2022-03-04T08:27:05Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@fabiop](https://discourse.cmake.org/u/fabiop)
#### Post date: [March 4, 2022, 8:27am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/1 "2022-03-04T08:27:05Z")
I would like to create a file containing the MD5 computed over another file, within the implementation of a custom target (so, not using file(MD5…)). Once I have done cmake -E md5sum filename, how to store the result in a file with an arbitrary name?
Thanks in advance for any help
---
### Author:  [@McMartin](https://discourse.cmake.org/u/McMartin)
#### Post date: [March 4, 2022, 8:30am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/2 "2022-03-04T08:30:21Z")
> [@fabiop](#):
>
> so, not using file(MD5…)
What is wrong with using `file(MD5 ...)`?
> [@fabiop](#):
>
> Once I have done cmake -E md5sum filename, how to store the result in a file with an arbitrary name?
How/where are you executing `cmake -E md5sum filename`?
Are you using CMake’s `execute_process` command? If yes, then you can use the `OUTPUT_FILE` argument. See [https://cmake.org/cmake/help/latest/command/execute\_process.html](https://cmake.org/cmake/help/latest/command/execute_process.html) for more details.
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### Author:  [@fabiop](https://discourse.cmake.org/u/fabiop)
#### Post date: [March 4, 2022, 8:36am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/3 "2022-03-04T08:36:34Z")
Sorry, my description was awful, i modified it
---
### Author:  [@McMartin](https://discourse.cmake.org/u/McMartin)
#### Post date: [March 4, 2022, 8:50am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/4 "2022-03-04T08:50:50Z")
In that case I would use an intermediate CMake script. For instance:
- `CMakeLists.txt`:
```cmake
add_custom_command(
OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/myfile.md5"
COMMAND
"${CMAKE_COMMAND}"
"-P"
"${CMAKE_CURRENT_SOURCE_DIR}/make_md5.cmake"
"${input_file}"
"${CMAKE_CURRENT_BINARY_DIR}/myfile.md5"
)
```
- `make_md5.cmake`:
```cmake
file(MD5 "${CMAKE_ARGV3}" md5_sum)
file(WRITE "${CMAKE_ARGV4}" "${md5_sum}")
```
---
### Author:  [@fabiop](https://discourse.cmake.org/u/fabiop)
#### Post date: [March 4, 2022, 8:54am UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/5 "2022-03-04T08:54:56Z")
This is what I was thinking about, and what I was trying to avoid. Doing operations at build time in our cmake code is leading to rewriting a lot of configure time operations within CMake scripts to be executed at build time…if there are no alternatives I think this is a great improvement area for CMake…
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 4, 2022, 8:38pm UTC](https://discourse.cmake.org/t/how-to-create-md5-file-within-add-custom-target/5156/6 "2022-03-04T20:38:27Z")
The script is run at build time. It’s just that the `add_custom_command` also runs CMake. This makes your build way more cross-platform than trying to suss out what the shell syntax for it is on whatever platform (while this is probably fine, once it gets complicated, you’ll likely prefer a script anyways).