Which nix-package provides a given file/binary/command?

Question

How can I figure out which nixpgs-package provides a given file/command, that may not be installed on the system?

Other package managers offer this functionality as follows:

• apt has apt-file
• rpm has --whatprovides
• yum has whatprovides

Does nix have a similar feature?

Context: I was trying to figure out which package provides grep, before realizing it was provided by the gnugrep package (who would have thought?). I am looking for a systematic way to answer questions like these, as to avoid the guessing game next time.

Things I have tried:

• nix-env -qa only searches through package names
• https://search.nixos.org/ only searches through package names

Answer 1

You can install the nix-index package, build the index and then use nix-locate command:

[nix-shell:~]$ nix-locate '/bin/grep'
perl532Packages.grepmail.out                     75,569 x /nix/store/i4krsr02b3yymqhzz9kbz066rkjkn5zl-perl5.32.1-grepmail-5.3111/bin/grepmail
perl530Packages.grepmail.out                     75,569 x /nix/store/vc2iv0zi7kb0fr04gahyx142i30xi0g6-perl5.30.3-grepmail-5.3111/bin/grepmail
patchutils_0_3_3.out                                  0 s /nix/store/yfl83agm8396xw9hir1rwvdanz13h9w5-patchutils-0.3.3/bin/grepdiff
patchutils.out                                        0 s /nix/store/wk1yk22f0f6ai478axaqr0yvwy6q7xl5-patchutils-0.3.4/bin/grepdiff
(patchutils.out)                                248,584 x /nix/store/6jysbyhc43sjvfiyh1bpvi1n3zbz212r-bootstrap-tools/bin/grep
ipinfo.out                                    4,293,096 x /nix/store/7p4g03bi15705ipbkrc7vhb42cvgc54f-ipinfo-2.0.1/bin/grepip
grepm.out                                         1,540 x /nix/store/mfhzjhz2f3mwbg1pq1diblqfdcmcffhs-grepm-0.6/bin/grepm
grepcidr.out                                     19,576 x /nix/store/7x10lzg5389flnjhfwh4xycqi835knfy-grepcidr-2.0/bin/grepcidr
gnugrep.out                                     271,716 x /nix/store/ba3bf20z5rmd9vgyzsgamvwvb3i1idfn-gnugrep-3.6/bin/grep
(unixtools.col.out)                              27,660 x /nix/store/0h4ih2jvl9gv3dnmld2vq5iyyv41cy7v-text_cmds-99/bin/grep

The Nix Cheatsheet provides a helpful list of corresponding commands in Nix and Ubuntu.

---

Indexing takes some time (depends on network speed and also the size). It can be reduced by using --filter-prefix '/bin/' when you're looking for utilities (8:10 -> 2:50 minutes in my case). Also interaction can be reduced by indexing right after invoking the shell:

$ nix-shell -p nix-index --command 'nix-index --version; time nix-index --show-trace --filter-prefix '/bin/'; return'
Nixpkgs Files Indexer 0.1.3
+ querying available packages
+ generating index: 55661 paths found :: 23483 paths not in binary cache :: 08533 paths in queue
Error: fetching the file listing for store path '/nix/store/siv7varixjdfjs17i3qfrvyc072rx55j-ia-writer-duospace-20180721' failed
Caused by: response to GET 'http://cache.nixos.org/siv7varixjdfjs17i3qfrvyc072rx55j.ls' failed to parse (response saved to /run/user/1000/file_listing.json.2)
Caused by: expected value at line 1 column 1
+ generating index: 66306 paths found :: 23630 paths not in binary cache :: 00000 paths in queue
+ wrote index of 2,742,453 bytes

real    2m50,553s
user    2m39,151s
sys 0m26,571s

[nix-shell:~]$ nix-locate /bin/grep
...
(irccloud.out)                                        0 s /nix/store/dv7klxqz8pmyml05nrs5f5ddd3hb9nsw-irccloud-0.13.0-usr-target/bin/grep
fpc.out                                             732 r /nix/store/4p5nx2csq7xmag9cbkmg54qzj6kxr71j-fpc-3.2.0/bin/grep.tdf
gnugrep.out                                     257,000 x /nix/store/z3q9q9549ci7kbdgyq99r6crnvrky6v3-gnugrep-3.7/bin/grep
grepm.out                                         1,596 x /nix/store/746bg318dq0wm1z23lllbg74ymdyac3r-grepm-0.6/bin/grepm
grepcidr.out                                     22,088 x /nix/store/sja30zvm5nw7ic7gwddc3h89rdgiyza4-grepcidr-2.0/bin/grepcidr
...

Answer 2

Unlike other Linux package managers that allow a package to install its files all over your system, Nix keeps all the files for a package together inside a single directory, which is named after the package. That directory lives inside /nix/store, and the name of that directory usually gives you a big clue about where the package was defined.

For example, if you have a utility on your PATH named nix-build and you are wondering where it came from, you could try this:

$ realpath $(which nix-build)
/nix/store/5hdmx9yk7gr71b98j4vh9271k0zg5jis-nix-2.2.1/bin/nix

Then we see that it comes from a package named nix. Roughly speaking, that is the name field from code that defined the derivation. The derivation name is not exactly the same as the attribute path that you use to refer to the derivation in the nixpkgs code, but it is still a good clue.