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Unix Find Command Tutorial

Dr. Nikolai Bezroukov Version 3.10



Unix find is a pretty tricky but very useful utility that can often fool even experienced UNIX professionals with ten on more years of sysadmins work under the belt. It can enhance functionality of those Unix utilities that does not include tree traversal (BTW GNU grep has -r option for this purpose and can be used on its own to perform tree traversal task: grep -r "search string" /tmp.).  There are several versions of find with the main two being POSIX find used in Solaris, AIX, etc and GNU find used in linux. GNU find can be installed on Solaris and AIX and it is actually a strong recommendation as there are some differences; moreover gnu find have additional capabilities that are often useful.

But find can do more then a simple tree traversal available with option -r (or -R) in many Unix utilities. Traversal provided by find can have excluded directory tree branches, can select files or directories using regular expressions, can be limited to specific typed of filesystem, etc. This capability is far above and beyond regular tree traversal of Unix utilities so find is a real Unix utility -- a useful enhancer of functionally of other utilities including both utilities that do not have capability to traverse the directory tree and those which have built-in simple recursive tree traversal

The idea behind find is extremely simple: this is a utility for searching files using the directory information and in this sense it is similar to ls. But it is more powerful then ls as it can provide " a ride" for other utilities and has an idiosyncratic mini-language for specifying queries, the language which probably outlived its usefulness but nobody has courage to replace it with a standard scripting language.

For obscure historical reasons find mini-language is completely different from all other UNIX commands: it has full-word options rather than single-letter options. For example, instead of a typical Unix-style option -f to match filenames (like in tar -xvf mytar.tar) find uses option -name. Also path to search can consist of multiple starting points, for example

find /usr /bin /sbin /opt -name sar # here we exclude non-relevant directories

In general you need to specify the set of starting points for a search through the file system first. The first argument starting with "-" is considered to be a start of "find expression". The latter can have side effects if you specified actions in the expression.

It is very important to understand that you can specify more than one directory as a starting point for the search. To look across the /bin and /var/html directory trees for filenames that contain the pattern *.htm*, you can use the following command:

find /usr /var/html -name "*.htm*" -print

Please note that you need quotes for any regex. Otherwise it will be evaluated immediately in the current context by shell.

It is simply impossible to remember all the details of this language unless you construct complex queries each day and that's why this page was created. Along with this page it make sense to consult the list of typical (and not so typical) examples which can be found in in Examples page on this site as well as in the links listed in Webliography. An excellent paper Advanced techniques for using the UNIX find command was written by Bill Zimmerly. I highly recommend to read it and then print and have a reference. Several examples in this tutorial are borrowed from the article.

The full find language is pretty complex and consist of several dozens of different predicates and options. There are two versions of this language: one implemented in POSIX find and the second implemented in GNU find which is a superset of POSIX find. That can make big difference in complex scripts. But for interactive use the differences is minor: only small subset of options is typically used on day-to-day basis by system administrators. Among them:

Other useful options of the find command include:

  1. -regex regex [GNU find only] File name matches regular expression. This is a match on the whole pathname not a filename. Stupidly enough the default regular expressions understood by find are Emacs Regular Expressions, not Perl regular expressions. It is important to note that "-iregex" option provide capability to ignore case.
  2. -perm permissions Locates files with certain permission settings. Often used for finding world-writable files or SUID files. See below
  3. -user Locates files that have specified ownership. Option -nouser locates files without ownership. For such files no user in /etc/passwd corresponds to file's numeric user ID (UID). such files are often created when tar of sip archive is transferred from other server on which the account probably exists under a different UID)
  4. -group Locates files that are owned by specified group. Option -nogroup means that no group corresponds to file's numeric group ID (GID) of the file
  5. -size Locates files with specified size. -size attribute lets you specify how big the files should be to match. You can specify your size in kilobytes and optionally also use + or - to specify size greater than or less than specified argument. For example:
    find /home -name "*.txt" -size 100k 
    find /home -name "*.txt" -size +100k 
    find /home -name "*.txt" -size -100k 

    The first brings up files of exactly 100KB, the second only files greater than 100KB, and the last only files less than 100KB.

  6. -ls list current file in `ls -dils' format on standard output.
  7. -type Locates a certain type of file. The most typical options for -type are as following:
    • d -Directory
    • f - File
    • l - Link

    For example to find a list of the directories use can use the -type specifier. Here's one example:

    find . -type d -print

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