Tuesday, February 2, 2010

Finding Files On The Command Line

SkyHi @ Tuesday, February 02, 2010
One of the things I like about Linux is the command line. I have used nautilus, gnome-commander, konqueror, kommander, dolphin and thunar to manage files in Linux and these file managers are great for what they do. But there are times when one simply wants to find a file when working on the command line without having to open a GUI application.
From the find man page:
GNU find searches the directory tree rooted at each given file name by evaluating the given expression from left to right, according to the rules of precedence until the outcome is known at which point find moves on to the next file name.
Find empty directories:
find /path -depth -type d -empty

Find empty files:
find /path -depth -type f -empty

Find a file with a specific name:
find /path -name name_of_file

Find a files with specific extensions:
find /path -name "*.given_extension"

Find files with specific permissions which have a ".txt. file extension:
find /path -name '*.txt' -perm 644

Find files with some given permissions:
find /path -perm -permision_bits

Find files with a given name and any extension:
find /path -name 'given_name.*'

Find files modified in the latest blocks of 24 hours:
find /path -mtime n
Where n is:
  • 0 for the last 24 hours
  • 1 for the last 48 hours
  • 2 for the last 72 hours

Find files that were accessed in the latest blocks of 24 hours:
find -atime n
Where n is:
  • 0 for the last 24 hours
  • 1 for the last 48 hours
  • 2 for the last 72 hours

Find files according to owner:
find /path -user root
One can also pipe find commands to the xargs command to execute commands on files.

Find and delete files:
find /path -name mytestfile | xargs rm
See man find and man xargs for more information about these powerful commands.
Many new Linux users are intimidated by the command line and this feeling should be overcome from the onset because the command line can be faster and more powerful than most GUI applications.

I find the "find" command very useful when some databases get corrupted. I use:
find /var/db/mysql -name "*.MYI" -exec myisamchk -r '{}' \;

To significantly speed up deletion of large numbers of files, finish the find command with a +, not a \;, thus:
find /path -iname "*somefile*" -exec rm "{}" +

Here is how you can find large files (or files larger then %)
find / -type f -size +10000k -exec ls -lh {} \; | awk '{ print $8 ": " $5 }'

An alternative way to find and delete files using only find.
find /path -name mytestfile -exec rm '{}' \;
Everything between -exec and \; get executed per file, and '{}' is replaced with the name of the file found.

This can be used to do just about anything with files. So for example, find and delete all CVS folders in a project:
find /path -name CVS -type d -exec rm -r '{}' \;

Create and md5 hash of all files in a folder

find /home/williamb/ -type f -exec md5sum '{}' \;



How to find files in Linux using 'find'
Files can be found under Linux in many different ways. Using the find tool is one of the best ways to find files. The find tool has a huge number of parameters which can be set so that Linux finds exactly those files that you were searching for. Many users use the find tool with just the basic parameters. They get the results that they were looking for. Unfortunately most of the users don't spend time to learn all about find. If they do, they can make excellent use of this tool and I am sure you would be surprised at the possibilities.

In case you just want to know where a particular file exists on your system, and nothing else is required, then use locate tool. Article No.20 explains how to use locate.

Here are a few ways to use find

$ find / -name 'program.c' 2>/dev/null
$ find / -name 'program.c' 2>errors.txt

Start searching from the root directory (i.e / directory)
Given search text is the filename rather than any other attribute of a file
Search text that we have entered. Always enclose the filename in single quotes.. why to do this is complex.. so simply do so.
Note : 2>/dev/null is not related to find tool as such. 2 indicates the error stream in Linux, and /dev/null is the device where anything you send simply disappears. So 2>/dev/null in this case means that while finding for the files, in case any error messages pop up simply send them to /dev/null i.e. simply discard all error messages.

Alternatively you could use 2>error.txt where after the search is completed you would have a file named error.txt in the current directory with all the error messages in it.

$ find /home/david -name 'index*'
$ find /home/david -iname 'index*'
The 1st command would find files having the letters index as the beginning of the file name. The search would be started in the directory /home/david and carry on within that directory and its subdirectories only.
The 2nd command would search for the same, but the case of the filename wouldn't be considered. So all files starting with any combination of letters in upper and lower case such as INDEX or indEX or index would be returned.

$ find -name met*
The above command would start searching for the files that begin with the letters 'met' within the current directory and the directories that are present within the current directory. Since the directory is not specified as the the second parameter, Linux defaults to using the current directory as the one to start the search in.

$ find /mp3collection -name '*.mp3' -size -5000k
$ find / -size +10000k
The 1st command would find within a directory called /mp3collection, only those mp3 files that have a size less than 5000 Kilobytes ( < 5MB)
The 2nd command would search from the / directory for any file that is larger than 10000k (> 10MB)

$ find /home/david -amin -10 -name '*.c'
$ find /home/david -atime -2 -name '*.c'
$ find /home/david -mmin -10 -name '*.c'
$ find /home/david -mtime -2 -name '*.c'

The 1st commmand searches for those files that are present in the directory /home/david and its subdirectoires which end in .c and which have been accessed in the last 10 minutes.
The 2nd command does the same but searches for those files that have been accessed in the last 10 hours.
The 3rd and the 4th commands do the same as the 1st and 2nd commands but they search for modified files rather than accessed files. Only if the contents of the files have been modified, would their names be returned in the search results.

$ find / -mount -name 'win*'
This command searches for files starting with the letters 'win' in their filenames. The only difference is that the mounted filesystems would not be searched for this time. This is useful when you have your Windows partitions mounted by default. And a search for 'win' might return many files on those partitions, which you may not be really interested in. This is only one use of -mount parameter.

$ find /mp3-collection -name 'Metallica*' -and -size +10000k
$ find /mp3-collection -size +10000k ! -name "Metallica*"
$ find /mp3-collection -name 'Metallica*' -or -size +10000k
Boolean operators such as AND, OR and NOT make find an extremely useful tool.
The 1st command searches within the directory /mp3-collection for files that have their names beginning with 'Metallica' and whose size is greater than 10000 kilobytes (> 10 MB).
The 2nd command searches in the same directory as above case but only for files that are greater than 10MB, but they should not have 'Metallica' as the starting of their filenames.
The 3rd command searches in the same directory for files that begin with 'Metallica' in their names or all the files that are greater than 10 MB in size.

he exec option is probably the most important feature of the find tool. The exec command allows you to execute a particular command on the results of the find command. A simple demonstration of this feature is shown below. Its upto your imagination to make maximum use of this feature. Suppose you wanted to see the details of the files (read, write, execute permission, file size, owner etc..) that have been returned as a search result you could do the following

$ find / - name 'Metallica*' -exec ls -l {\}\ \;

This command would find all the files on your system that begin with the letters 'Metallica' and would then execute the 'ls -l' command on these files. So basically you would be able to see the details of the files that were returned according to your search criteria.

The words following the -exec option is the command that you want to execute i.e. ls -l in this case.
{\}\ is basically an indicator that the filenames returned by the search should be substituted here.
\; is the terminating string, and is required at the end of the command