Bash - 14 - File Searching

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.

‘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.

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

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"

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.

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.

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

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.

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'