In Linux Bash language command line, there are cases when you want to know which line number a regex match is on.
ag hogehoge links.txt | ag --only-matching "^\d+"
# or
grep -Fn hogehoge links.txt | sed -Ee 's/^([0-9]+).*/\1/g'ag is simpler, but ag can’t be manually installed, so it may not be available on rental servers. In that respect, grep can be used even on servers like Xserver. It’s a matter of choosing the right tool.
bash - How to get the line number of a match? - Stack Overflow