user@home:/usr/include/boost$ fsrc
Usage  : fsrc [options] term
Options:
  -d [ --dir ] arg      Search folder
  -e [ --ext ] arg      Search only in files with extension <arg>, equiv. to 
                        --glob '*.ext'
  -f [ --files ]        Only print filenames
  -g [ --glob ] arg     Search only in files filtered by <arg> glob, e.g. 
                        '*.txt'; overrides --ext
  -h [ --help ]         Help
  --html                open web page with results
  -i [ --ignore-case ]  Case insensitive search
  --no-git              Disable search with 'git ls-files'
  --no-colors           Disable colorized output
  --no-piped            Disable piped output
  --no-uri              Print w/out file:// prefix
  --piped               Enable piped output
  -q [ --quiet ]        only print status
  -r [ --regex ]        Regex search (slower)

Build : v0.24 from Jun 18 2021
Web   : https://github.com/elsamuko/fsrc
user@home:/usr/include/boost$ fsrc filesystem
Searching for "filesystem" in folder:

...
/usr/include/boost/spirit/home/x3/support/utility/testing.hpp
L  11 : #include <boost/filesystem.hpp>
L  12 : #include <boost/filesystem/fstream.hpp>
L  16 :     namespace fs = boost::filesystem;
L 205 :         catch (const fs::filesystem_error& ex)
L 215 :         boost::filesystem::ifstream file(p);

Times: Recurse 22 ms, Read 83 ms, Search 14 ms, Collect 0 ms, Print 28 ms
Found 449 matches in 68/12520 files (108658 kB) in 34 ms
user@home:/usr/include/boost$