To find files on Linux, find is the tool, and the shape is always the same: find, then where to look, then what to match. find . -name '*.log' lists every .log file under the current folder; swap the dot for /var/log to search there instead. From that base you filter: -type f for files or d for directories, -size +100M for the big ones, -mtime -7 for things changed in the last week. Then you can act on the matches with -delete or -exec. It ships on every Linux and macOS system. Here's the everyday syntax, the filters you will actually use, and the safe way to delete matches without wiping the wrong thing.
The short answer
find . -name '*.log' lists matching files below the current folder. Filter
with -type, -size and -mtime, then act with -delete or -exec. Always
run it without -delete first to check the list.
Find by name
find . -name '*.log' That walks the current folder and everything under it. Use -iname for a
case-insensitive match.
Filter by size or age
find /var/log -name '*.log' -mtime +30 Hunting for what is eating your disk? Match on size and files only:
find . -type f -size +100M Act on the results, carefully
find . -name '*.tmp' -delete Run it once without -delete and read the list first. find does exactly
what you say, including deleting a tree you did not mean to.
Other handy filters
-type d for directories, -empty for empty files or folders, -newer ref
for anything modified more recently than a reference file, and -exec command {} + to run a command on every match when -delete is not what you need.
Frequently asked questions
How do I find a file by name?
find . -name '*.conf' lists every .conf file under the current directory. Use -iname instead of -name to ignore case. Keep the quotes around the pattern so the shell does not expand the star before find sees it.
How do I find files bigger than a certain size?
Use -size with a suffix: -size +100M for larger than 100 MB, -size -1k for smaller than 1 KB. Combine it with -type f so you match only files, not directories.
How do I find files changed recently?
Use -mtime in days: -mtime -7 means modified in the last 7 days, -mtime +30 means older than 30 days. For minutes rather than days, -mmin works the same way.
How do I delete the files I found, safely?
Run the find without -delete first and read the list. Only when it is exactly right, append -delete (or -exec rm to act on each one). Deleting blind is how people erase the wrong tree, so always look before you add -delete.