File Search

grep

Command	Effect
grep pattern file	Prints matching lines.
grep -rn pattern dir	Searches recursively, with line numbers.
grep -ri pattern dir --include='*.yml'	Case-insensitive, only in matching files.
grep -l pattern *	Prints only the names of matching files.
grep -v pattern file	Prints lines that don’t match.
grep -C 3 pattern file	Adds three lines of context around each match.
grep -E 'error|warn' file	Extended regex, here either word.

ripgrep (rg pattern) searches recursively by default, skips files from .gitignore and is much faster on large trees.

find

find walks a directory tree and applies tests to every entry; all tests must match.

Command	Finds
find /home -name '*.log'	Files by name (-iname ignores case).
find /home -type d -name cache	Only directories.
find /home -size +100M	Files larger than 100 MiB.
find /var/log -mtime -1	Files changed within the last 24 hours.
find . -name '*.tmp' -delete	Deletes matches. Run without -delete first.
find . -name '*.sh' -exec chmod +x {} +	Runs a command on all matches.
find / -xdev -user alice	Files of a user, without descending into other filesystems.

Caution

Quote patterns: unquoted, the shell expands *.log to the matching files in the current directory before find sees it.

Programs and packages

Command	Effect
command -v app	Path of the program the shell would run (also finds aliases and functions).
type -a app	All programs, aliases and functions with that name.
rpm -qf /usr/bin/app	Which package owns a file (Fedora/RHEL); dpkg -S on Debian.
dnf list --installed	Installed packages (Fedora/RHEL); apt list --installed on Debian.