Linux offers several methods to search for files or directories, with the find command being one of the most powerful and versatile tools.

File Browser

A file browser provides a graphical interface for searching files. It includes:

• A search bar where you can enter search terms.
• Drop-down menus to filter by criteria such as modification date, file type, or size.

In some cases, file browsers also allow full-text searching, where the search examines both the filename and the contents of text files.

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'find' Command

The find command is used to search for files and directories based on specific criteria. It’s a flexible and powerful tool with many options and actions.

To start using find, specify the directory in which to search and the search criteria:

find [directory] [expression]

find path_list selection_criteria action

To list all files and directories under the current directory:

$ find .

This command will recursively list all files and directories starting from the current directory.

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Filtering by Type

You can filter the search results by file type using the -type option:

-type d: Lists only directories.

$ find . -type d

-type f: Lists only files.

$ find . -type f

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Searching by Name

To search for files based on their name, use the -name option with the string or pattern you're looking for.

$ find . -name "*.txt"

This finds all .txt files in the current directory and all its subdirectories. (* gets expanded before expansion)

Note: Enclose the pattern in quotes to prevent shell expansion of *. Otherwise, it will only search for files named literally *.txt.

find /etc -name "*.conf"

to locate files ending in .conf in the /etc directory.

To search case-insensitively, use -iname:

$ find . -iname "*.txt"

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Combining 'find' with Other Commands

You can use find with other commands. For example, to count the lines in all .txt files found by find, use command substitution:

$ wc -l $(find . -name "*.txt")

This will pass all .txt files to wc -l to count their lines.

To count lines in all .dat files and sort the results numerically:

$ wc -l $(find . -name "*.dat") | sort -n

This command finds all .dat files, counts their lines, and sorts the results.

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There are three categories of options

1. Search criteria: which -name and -iname are part
2. Options that alter find's behavior.
3. Actions: which control what should happen when it has located an item.

The search criteria options
Most but not all search expression require a parameter.
n indicates an integer (time, size or UID/GID)
file indicates filename.
test indicates a set of permissions.
type represents file type or file system type.
name is user or group name.
pattern is regular expression.

[+-]n for time and size, if the number is by itself then it tries to find an exact match.
If the integer is preceded by + then find looks for matches where the property is greater than the integer.
-5 looks for property values less than 5.

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Search Criteria Options

find offers many search criteria to refine searches, including time-based, size-based, and type-based options.

Time-Based Options

These options let you search for files based on when they were last accessed or modified:

• -amin [+-]n: Files accessed n minutes ago (use + for older, - for more recent).

$ find . -amin -5  # Files accessed in the last 5 minutes

• -mmin [+-]n: Files modified n minutes ago.

$ find . -mmin -100  # Files modified in the last 100 minutes

• -atime [+-]n: Files accessed n days ago.
• -mtime [+-]n: Files modified n days ago.

$ find . -mtime +10  # Files modified more than 10 days ago

Size-Based Options

You can search for files based on their size:

• -size [+-]n: Files of a specific size. Use suffixes like c (bytes), k (kilobytes), M (megabytes), etc.

$ find . -size +1M  # Files larger than 1MB

n can be followed by b (512-byte blocks), c (byte), w (2-word bytes), k (kilobytes), M (megabytes) and G (Gigabytes)
-size +1024c -size +1k
-size 1000c means exactly 1000 bytes in size.
-size -1000c means less than 1000 bytes in size.

File Type Options

You can filter by file type:

• -type d: Directories
• -type f: Regular files
• -type l: Symbolic links
• (s - socket, p - pipe, c - characters, b - block)

$ find . -type f  # Regular files

Permission-Based Options

Search for files based on their permissions:

• -perm: Files with specific permissions. For example, to find files with 755 permissions:

$ find . -perm 755

Owner and Group Search

Search for files based on their owner or group:

• -user username: Files owned by a specific user.

$ find . -user alice  # Files owned by 'alice'

• -group groupname: Files belonging to a specific group.

$ find . -group staff  # Files belonging to the 'staff' group

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Logical Operators

You can combine multiple conditions using logical operators:

-and or -a: Represents ANDed conditions.

$ find . -size +100c -and -size -200c
$ find . -size +100c -size -200c
$ find . -size +100c -a -200c

# Files between 100 and 200 bytes

-or or -o: Represents ORed conditions.

$ find . -size +100c -o -name "*.txt"  
# Files larger than 100 bytes OR .txt files

-not or !: Negates a condition.

$ find . -not -type d  
# Files that are not directories

find /dev ! -type c
find /dev -not -type c
# All files that are not character type.

Without parenthesis, not is applied first, followed by and, then or.

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Depth and Mounting Options

• -maxdepth: Limit the search to a certain depth.

$ find . -maxdepth 2  # Search only two levels deep

• -mount: Prevents find from descending into other mounted filesystems.

$ find . -mount -name "*.txt"  # Only search the current filesystem

3. Actions with find

You can specify actions to take on the found files using options like -exec, -delete, and others.

• -delete: Deletes all files that match the criteria.

$ find . -empty -delete  # Delete all empty files and directories

• -exec: Executes a command on each found file. For example, to count lines in each file:

$ find . -type f -exec wc -l {} \;  # Count lines in each file

• -ok: Similar to -exec, but asks for confirmation before executing the command on each file.

$ find . -type f -exec chmod 755 {} \;  # Change permissions, with confirmation

• -ls: Lists the files using ls -l format.

$ find . -name "*.txt" -ls

• -prune: Prevents find from descending into directories.

$ find . -name "*.txt" -prune  # Skip directories

• -quit: Stops the search after finding the first match.

$ find . -name "*.txt" -quit  # Stop after finding the first .txt file

4. Other Methods of Locating Files

which: Finds the path of an executable file which is present in PATH.

$ which name

$ which ls  
# Locate the 'ls' command

whereis: Locates binary, source, and man pages for a command (not reliant on PATH).

$ whereis man  # Locate the 'man' command and its files

locate: Uses a database to quickly find files. The database must be updated with updatedb.

$ locate man  # Locate files related to 'man'

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