Revision 507913 of "Find" on knwiki

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In [[Unix-like]] and some other [[operating system]]s, <code>'''find'''</code> is a [[command-line utility]] that [[Search engine (computing)|searches]] through one or more [[directory tree]]s of a [[file system]], locates [[Computer file|file]]s based on some [[user (computing)|user]]-specified criteria and applies a user-specified action on each matched file. The possible search criteria include a [[pattern matching|pattern]] to match against the [[file name]] or a time range to match against the modification time or access time of the file. By default, <code>find</code> returns a list of all files below the current [[working directory]].

The related <code>'''[[GNU locate|locate]]'''</code> programs use a database of indexed files obtained through <code>find</code> (updated at regular intervals, typically by <code>'''[[cron]]'''</code> job) to provide a faster method of searching the entire filesystem for files by name.  This sacrifices overall efficiency (because filesystems are regularly interrogated even when no users needs information) and absolute accuracy (since the database is not updated in real time) for significant speed improvements (particularly on very large filesystems).  On fast systems with small drives, <code>locate</code> is not necessary or desirable.

== Find syntax ==
{{expand section|date=August 2008}}

<code>'''find [-H] [-L] [-P] [path...] [expression]'''</code>

The three options control how the <code>find</code> command should treat symbolic links. The default behaviour is to never follow symbolic links. This can be explicitly specified using the -P flag. The -L flag will cause the <code>find</code> command to follow symbolic links. The -H flag will only follow symbolic links while processing the command line arguments.

At least one path must precede the expression. <code>Find</code> is capable of interpreting [[Wildcard character|wildcards]] internally and commands must be constructed carefully in order to control [[Glob (programming)|shell globbing]].

Expression elements are whitespace-separated and evaluated from left to right.  They can contain logical elements such as AND (-a) and OR (-o) as well as more complex predicates.

The [[GNU findutils|GNU]] <code>find</code> has a large number of additional features not specified by POSIX.

== POSIX protection from infinite output ==

Real-world filesystems often contain looped structures created through the use of [[hard link|hard]] or [[symbolic link|soft links]].  The [[POSIX|POSIX standard]] requires that
 The <code>find</code> utility shall detect infinite loops; that is, entering a previously visited
 directory that is an ancestor of the last file encountered. When it detects an infinite
 loop, <code>find</code> shall write a diagnostic message to standard error and shall either recover
 its position in the hierarchy or terminate.

==Examples==
===From current directory===
 find . -name 'my*'
This searches in the current directory (represented by a period) and below it, for files and directories with names starting with ''my''. The quotes avoid the [[shell (computing)|shell]] expansion — without them the shell would replace ''my*'' with the list of files whose names begin with ''my'' in the current directory. In newer versions of the program, the directory may be omitted, and it will imply the current directory.

===Files only===
 find . -name "my*" -type f
This limits the results of the above search to only regular files, therefore excluding directories, special files, pipes, symbolic links, etc. ''my*'' is enclosed in quotes as otherwise the shell would replace it with the list of  files in the current directory starting with ''my''...

===Commands===
The previous examples created listings of results because, by default, <code>find</code> executes the '-print' action.   (Note that early versions of the <code>find</code> command had no default action at all; therefore the resulting list of files would be discarded, to the bewilderment of users.) 

 find . -name "my*" -type f -ls
This prints extended file information.

===Search all directories===
 find / -type f -name "myfile" -print
This searches every file on the computer for a file with the name ''myfile'' and prints it to the screen. It is generally not a good idea to look for data files this way.  This can take a considerable amount of time, so it is best to specify the directory more precisely.  Some operating systems may mount dynamic filesystems that are not congenial to <code>find</code>.

===Search all but one directory subtree===
 find / -path excluded_folder -prune -o -type f -name myfile -print
This searches every folder on the computer except the subtree ''excluded_folder'' for a file with the name ''myfile''.  It will not detect directories, devices, links, doors, or other "special" filetypes.

===Specify a directory===
 find /home/weedly -name "myfile" -type f -print
This searches for files named ''myfile'' in the ''/home/weedly'' directory, the home directory for userid ''weedly''.  You should always specify the directory to the deepest level you can remember.

===Search several directories===
 find local /tmp -name mydir -type d -print
This searches for directories named ''mydir'' in the ''local'' subdirectory of the current working directory and the ''/tmp'' directory.

===Ignore errors===
If you're doing this as a user other than root, you might want to ignore permission denied (and any other) errors.  Since errors are printed to [[stderr]], they can be suppressed by redirecting the output to /dev/null.  The following example shows how to do this in the bash shell: 
 find / -name "myfile" -type f -print 2>/dev/null

If you are a [[C shell|csh]] or [[tcsh]] user, you cannot redirect [[stderr]] without redirecting [[stdout]] as well.  You can use sh to run the <code>find</code> command to get around this:
 sh -c find / -name "myfile" -type f -print 2>/dev/null

An alternate method when using [[C shell|csh]] or [[tcsh]] is to pipe the output from [[stdout]] and [[stderr]] into a [[grep]] command. This example shows how to suppress lines that contain permission denied errors.
 find . -name "myfile" |& grep -v "Permission denied"

===Find any one of differently named files===
 find . \( -name "*jsp" -o -name "*java" \) -type f -ls

The <code>-ls</code> option prints extended information, and the example finds any file whose name ends with either 'jsp' or 'java'. Note that the parentheses are required. Also note that the operator "or" can be abbreviated as "o". The "and" operator is assumed where no operator is given.  In many shells the parentheses must be escaped with a backslash, "\(" and "\)", to prevent them from being interpreted as special shell characters. The <code>-ls</code> option and the <code>-or</code> operator are not available on all versions of <code>find</code>.

===Execute an action===
 find /var/ftp/mp3 -name "*.mp3" -type f -exec chmod 644 {} \;
This command changes the [[File system permissions|permissions]] of all files with a name ending in ''.mp3'' in the directory ''/var/ftp/mp3''. The  action is carried out by specifying the option <code>-exec [[chmod]] 644 {} \;</code> in the command. For every file whose name ends in <code>.mp3</code>, the command <code>chmod 644 {}</code> is executed replacing <code>{}</code> with the name of the file. The semicolon (backslashed to avoid the shell interpreting it as a command separator) indicates the end of the command. Permission <code>644</code>, usually shown as <code>rw-r--r--</code>, gives the file owner full permission to read and write the file, while other users have read-only access. In some shells, the <code>{}</code> must be quoted.

Note that the command itself should *not* be quoted; otherwise you get error messages like

 find: echo "mv ./3bfn rel071204": No such file or directory

which means that <code>find</code> is trying to run a file called 'echo "mv ./3bfn rel071204"' and failing.

If running under Windows, don't include the backslash before the semicolon:

 find . -exec grep blah {} ;

If you will be executing over many results, it is more efficient to pipe the results to the [[xargs]] command instead.  xargs is a more modern implementation, and handles long lists in a more intelligent way.  The print0 option can be used with this.

The following command will ensure that filenames with whitespaces are passed to the executed COMMAND without being split up by the shell.  It looks complicated at first glance, but is widely used.

 find . -print0 | xargs -0 COMMAND

The list of files generated by <code>find</code> (whilst it is being generated) is simultaneously [[Pipe (Unix)|piped]] to xargs, which then executes COMMAND with the files as arguments.  See [[xargs]] for more examples and options.

===Search for a string===
This command will search for a string in all files from the /tmp directory and below:

 find /tmp -exec grep "search string" '{}' /dev/null \; -print

The <tt>[[/dev/null]]</tt> argument is used to show the name of the file before the text that is found. Without it, only the text found is printed.  An equivalent mechanism is to use the "-H" or "--with-filename" option to grep:

 find /tmp -exec grep -H "search string" '{}' \; -print

GNU grep can be used on its own to perform this task:

 grep -r "search string" /tmp

Example of search for "LOG" in jsmith's home directory
 find ~jsmith -exec grep "LOG" '{}' /dev/null \; -print
 /home/jsmith/scripts/errpt.sh:cp $LOG $FIXEDLOGNAME
 /home/jsmith/scripts/errpt.sh:cat $LOG
 /home/jsmith/scripts/title:USER=$LOGNAME

Example of search for the string "ERROR" in all xml files in the current directory and all sub-directories
 find . -name "*.xml" -exec grep "ERROR" '{}' \; -print

The double quotes (" ") surrounding the search string and single quotes (<nowiki>' '</nowiki>) surrounding the braces are optional in this example, but needed to allow spaces and other special characters in the string.

===Search for all files owned by a user===
 find . -user <userid>

===Search in case insensitive mode===
 find . -iname "MyFile*"

If the <code>-iname</code> switch is not supported on your system then workaround techniques may be possible such as:

 find . -name "[mM][yY][fF][iI][lL][eE]*"

This uses [[Perl]] to build the above command for you:

 echo "'MyFile*'" |perl -pe 's/([a-zA-Z])/[\L\1\U\1]/g;s/(.*)/find . -name \1/'|sh

===Search files by size===
Example of searching files with size between 100 kilobytes and 500 kilobytes.
 find . -size +100k -a -size -500k

===Search files by name and size ===
 find /usr/src -not \( -name "*,v" -o -name ".*,v" \) '{}' \; -print 

This command will search in the /usr/src directory and all sub directories. All files that are of the form '*,v' and '.*,v' are excluded. Important arguments to note are:
    -not means the negation of the expression that follows
    \( means the start of a complex expression.
    \) means the end of a complex expression.
    -o means a logical or of a complex expression.
       In this case the complex expression is all files like '*,v' or '.*,v' 

 for file in `find /opt \( -name error_log -o -name 'access_log' -o -name 'ssl_engine_log' -o -name 'rewrite_log' -o
 -name 'catalina.out' \) -size +300000k -a -size -5000000k`; do cat /dev/null > $file; done

The units should be one of [bckw], 'b' means 512-byte blocks, 'c' means byte, 'k' means kilobytes and 'w' means 2-byte words. The size does not count indirect blocks, but it does count blocks in sparse files that are not actually allocated.

==See also==
*[[GNU locate]], a Unix search tool based on a prebuilt database therefore faster and less accurate than <code>find</code>
*[[mdfind]], a similar utility that utilizes metadata for [[Mac OS X]] and [[Darwin (operating system)|Darwin]]
*[[List of Unix programs]]
*[[List of DOS commands]]
*[[find (command)]], a DOS and Windows command that is very different from UNIX <code>find</code>
*[[findutils]]

==External links==
*{{man|cu|find|SUS|find files}}
*{{man|1|find||search for files in a directory hierarchy}}
*[http://doc.cat-v.org/unix/find-history A story on the origins of the Unix find command].
*[http://www.gnu.org/software/findutils/ GNU Findutils] - Comes with the [[xargs]] and [[GNU locate|locate]] commands.
*[http://www.gnu.org/software/findutils/manual/html_mono/find.html Official webpage for GNU find]
*[http://www.softpanorama.org/Tools/Find/find_mini_tutorial.shtml Softpanorama find tutorial]
*[http://www.enciclopedia.galeon.com/find.html Exercises "Find"]
*[http://find.unixpin.com/ "Find helper" - unix "find" wizard]
*[http://www.oracle.com/technology/pub/articles/calish-find.html Guide to Linux Find Command Mastery]
*[http://www.shell-fu.org/lister.php?tag=find Top 'find' commands - interesting usage]

{{Unix commands}}

[[Category:Searching]]
[[Category:Standard Unix programs]]
[[Category:Unix SUS2008 utilities]]

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