View source for Find notes

[[Category:Engineering]]

== exec versus xargs ==

You may notice that some people will pipe `find` output into `xargs`, but other people tell `find` to start a command using -exec. What is the difference? The difference is that xargs is faster. It will group arguments and feed batches to the subcommand, so it doesn't have to start a new instance of the subcommand for every argument.

I think -exec is easier because you can use filename more than once in the -exec argument. It's easier for me to express exactly what I want to be executed. 

Find also his its own built-in form of xargs using the {}+ instead of {}\; in an -exec or -execdir section. Like using xargs the replacement string must be the only and last in the statement to be executed.

== Find and delete old files with `find` and cron ==

Put in /etc/cron.daily. This automatically deletes Spam older than 30 days from my Spam folder.

<pre>
#!/bin/sh
find /home/vpopmail/domains/noah.org/noah/Maildir/.Spam/cur/ -type f -mtime +30 -exec rm -f {} \;
</pre>

More CPU efficient:

<pre>
#!/bin/sh
find /home/vpopmail/domains/noah.org/noah/Maildir/.Spam/cur/ -mtime +30 | xargs rm
</pre>

== find older or newer files by minutes ==

Find files older than 30 minutes:
<pre>
find . -type f -mmin +30
</pre>
Find files newer than 30 minutes:
<pre>
find . -type f -mmin -30
find . -type f -not -mmin +30
</pre>

== delete files older than given minutes ==

This deletes files older than one hour (60 minutes):
<pre>
find . -type f -mmin -60 -exec rm -f {} \;
</pre>

== Find files newer than 1 day ==

Find files less than 1 day old.

<pre>
find . -type f -mtime -1
</pre>

== Find devices recently added ==

This is a good trick to poll any directory for file updates. See also [[inotify]].

<pre>
find /dev -maxdepth 1 -mmin -1
</pre>

== set full access to all for an entire subdirectory ==

Directories need 'a+rwx' whereas files need 'a+rw'. You don't want to remove execute permissions from all files or add it from all files (otherwise you could just do something stupid like, `chmod -R 777 .`).

<pre>
find . \( -type d -exec chmod a+rwx '{}' \; \) -or \( -type f -exec chmod a+rw '{}' \; \)
find . \( -type d -exec chmod a+rwx '{}' \; \) , \( -type f -exec chmod a+rw '{}' \; \)
</pre>

See also the note on how to [[#copy user permissions to group permissions]].

== copy user permissions to group permissions ==

Often you want group permissions to be identical as user permissions for an entire directory structure. This often happens with htdoc directories on web sites. The typical newbie mistake is to execute a massive `chmod -R a+rwx .` in an attempt to "get rid of permission problems". The following is a <em>slightly</em> more surgical:

<pre>
find . -exec /bin/sh -c 'chmod g=`ls -ld "{}" | cut -c2-4 | tr -d "-"` "{}"' \;
</pre>

This is also really slow. It forks a shell for every single file and directory in the current path directory structure. Run time: 95m 36.895s on a directory tree with 111645 files. This was a system with a slow drive (disk read: 8.43 MB/sec), but even so most of the poor performance is due to exec'ing a shell.

== List all extensions in the current directory ==

This came in handy when I was trying to find out exactly what mime-types I need to care about.

<pre>
find . -print0 | xargs -L 1 -0 basename | sed -e "s/.*\(\\.\\s*\)/\\1/" | sort | uniq > /tmp/types
</pre>

The -print0 option tells find to null-terminate filenames. The -0 option for xargs tells it to read null-terminated strings. These two options are used to handle filenames that have special characters such as quotes or line-feeds. If you don't do this then you may get the following error:

<pre>
xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option
</pre>

== massive recursive grep ==

Grep has a recursive option, but you can fine tune a recursive grep wtih `find` -- you can make much more complicated expressions for the types of files you want to grep through. The main to remember when using `grep` with `find` is that you probably want the -H option on grep. This prints the filename along with the match.

<pre>
find . -exec grep -H PatternToFind {} \;
</pre>

== find duplicates of files (dedupe) ==

This will list files with duplicates. It compares all files under the given directory. This ignores .svn directories and files of size 0.

This needs a little more work... It would be more efficient if it ignored all files that have a unique size, but then it's a slippery slope into writing a full-blown script. I would also like to get rid of the tmp file. This could be done by using `sed` to rearrange the fields so that the crc is at the end of the line, and then use the '''-f''' option of `uniq` to ignore all but the last field when comparing lines.

<pre>
find . . -name .svn -prune -o -size 1 \! -type d -exec cksum {} \; | sort | tee /tmp/f.tmp | cut -f 1,2 -d ' ' | uniq -d | grep -hif - /tmp/f.tmp
</pre>

=== find duplicates on Mac OS X ===

The Mac does not have the `md5sum` command, but it has the `md5` command, which formats the output differently. Note that this only prints the filename of duplicates, not the original filename. It should be possible to modify this command to use `chsum`, which is faster. The crc field would have to be moved to the end of the line using `sed` because the `uniq` command has an option to skip leading fields, but it has no option to look at only a single field in the middle of other fields.
<pre>
find . -type f -exec md5 '{}' ';' | sort | uniq -f 3 -d | sed -e "s/.*(\(.*\)).*/\1/" 
</pre>
If you want to delete the duplicate you can pipe the output through `xargs`. This works because the original filename is not printed.
<pre>
find . -type f -exec md5 '{}' ';' | sort | uniq -f 3 -d | sed -e "s/.*(\(.*\)).*/\1/" | xargs rm
</pre>

== find unique files in between two directories of hard-linked copies ==

Backups that create a rotating backup often hard-link unchanged files between each rotation set. This saves disk space. Files that have changes are copied normally, so they don't have additional hard-links. Sometimes it is useful to compare two backup sets and generate a list of the files that changed between each set. This could be done with file hashes, but that would be slow. We can use the fact that files that are identical in two separate backup sets will have the same inode number. Files that are changed will have different inode numbers.

<em>This is a work in progress...</em>

<pre>
cat <(find BACKUP_SET_1 ! -type d -exec ls -1i "{}" \;) <(find BACKUP_SET_2 ! -type d -exec ls -1i "{}" \;) | sort | cut -d ' ' -f 2-,1 | uniq -u -f 1
</pre>