Filename

Filenames

grep -rli file*	Pattern match
grep -rli "filename" /path/to/search	Recursive
ls -R [directory] | grep "filename"	Recursive
find / -a -iname "filename"	Case insensitive
find / -a -type f -name password.txt	Recursive exact match
find / -a -name "pat*tern"	Pattern match "pat" and ending with "tern"
find / -a -type d -name config	Exact directory match
find / -a -type d -name "\*687-250\*"	Pattern directory match
find / -a -regex "regex_pattern"	Regex
locate "[filename]"	Uses a database updated by updatedb to quickly locate files
locate -i "[filename]"	Case-insensitive

Use extended regex syntax:

find / -a -regextype egrep -regex "pat.+?ern"

Use Perl regex syntax:

find / -a -regextype perl -regex "^user_[0-9]+.sh$"

Uses xargs for efficiency with a large number of files

find / -a -type f -print0 | xargs -0 grep -l "[string]"

Finds files by name and then executes ls -lh:

find / -a -type f -name "[filename]" -exec ls -lh {} +

Find development tools and supported languages:

find / -a -name perl*
find / -a -name python*
find / -a -name gcc*

File Extensions

ls [directory]/*.ext	Not Recursive
find / -a -type f \( -name "*.txt" -o -name "*.sh" \)	Multiple file extensions.
find / -a -type f -name "*.txt"	Recursive
find / -a -type f -iname "*.txt"	Case-insensitive.
find / -a -type f -regex ".*\.txt"	Use regular expressions.
find / -a -regextype posix -regex ".+\.log$"	Matches all files ending with .log, using POSIX regex syntax.
grep -rli "\.txt$" /path/to/search	Recursive
grep -rli --include=\*.ext "pattern" [directory]	Recursively searches for files with the .ext extension containing "pattern" in the specified directory.

Search Multiple Dirs

find /opt /usr /var -a -type f -name foo.scala	Search specific directories
find /directory* -name foo.txt	Wildcard

Loop: Iterates through each directory and runs the find command inside each, effectively searching them all.

for dir in /path/to/directory1 /path/to/directory2 ; do
  find "$dir" -name your_search_term
done

Inverse

grep -L	Lists files that do not contain a specified pattern.
ls / | grep -v "[pattern]"	Lists files in the root directory that do not match the specified pattern.
find / -a -not -name "[pattern]"	Finds files not matching a specific pattern.
find / -a -type f -not -name "*.html"	Finds files that do not end in ".html".
find / -a ! -name "[pattern]"	An alternative to -not, finds files not matching a specific pattern.
find / -a ! -name "pattern1" ! -name "pattern2"	Finds files not matching multiple patterns.
find / -a -type f ! -exec grep -q "[pattern]" {} \; -print	Finds files that do not contain a specified pattern using -exec.
find / -a -type f -print0 | xargs -0 grep -L "[pattern]"	Finds files that do not contain a specified pattern using xargs.
awk '!/[pattern]/' [file]	Uses awk to print lines from a file that do not match a specific pattern.
sed -n '/[pattern]/!p' [file]	Uses sed to print lines from a file that do not match a specific pattern.

Weird Filenames

find / -a -type d -name " \*" -exec ls -ladtri {} 2>/dev/null +	Directories with a space
find / -a -type f -name " \*" -exec ls -latriQ {} 2>/dev/null +	Files with a space
find / -a -type f -name '*[![:alnum:]_\-\.]*'	Files with non-alphanumeric characters in their filenames.
find / -a -type f -regex '.*[^[:alnum:]_\-\.].*'	Files with non-alphanumeric characters in their filenames using regex.

Executables

which grep	Single binary
which python java gcc	Multiple binaries
type ls	Shows how the command is interpreted by the shell.
command -v ls	Shows how the command is interpreted by the shell.
which -a python	All instances of "python" in the path.