Finding Files

Edition 1.1, for GNU find version 4.1

November 1994

Copyright © 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

1 Introduction

This manual shows how to find files that meet criteria you specify, and how to perform various actions on the files that you find. The principal programs that you use to perform these tasks are find, locate, and xargs. Some of the examples in this manual use capabilities specific to the GNU versions of those programs.

GNU find was originally written by Eric Decker, with enhancements by David MacKenzie, Jay Plett, and Tim Wood. GNU xargs was originally written by Mike Rendell, with enhancements by David MacKenzie. GNU locate and its associated utilities were originally written by James Woods, with enhancements by David MacKenzie. The idea for ‘find -print0’ and ‘xargs -0’ came from Dan Bernstein. Many other people have contributed bug fixes, small improvements, and helpful suggestions. Thanks!

Mail suggestions and bug reports for these programs to bug-gnu-utils@prep.ai.mit.edu. Please include the version number, which you can get by running ‘find --version’.

1.1 Scope

For brevity, the word file in this manual means a regular file, a directory, a symbolic link, or any other kind of node that has a directory entry. A directory entry is also called a file name. A file name may contain some, all, or none of the directories in a path that leads to the file. These are all examples of what this manual calls “file names”:

parser.c
README
./budget/may-94.sc
fred/.cshrc
/usr/local/include/termcap.h

A directory tree is a directory and the files it contains, all of its subdirectories and the files they contain, etc. It can also be a single non-directory file.

These programs enable you to find the files in one or more directory trees that:

• have names that contain certain text or match a certain pattern;
• are links to certain files;
• were last used during a certain period of time;
• are within a certain size range;
• are of a certain type (regular file, directory, symbolic link, etc.);
• are owned by a certain user or group;
• have certain access permissions;
• contain text that matches a certain pattern;
• are within a certain depth in the directory tree;
• or some combination of the above.

Once you have found the files you’re looking for (or files that are potentially the ones you’re looking for), you can do more to them than simply list their names. You can get any combination of the files’ attributes, or process the files in many ways, either individually or in groups of various sizes. Actions that you might want to perform on the files you have found include, but are not limited to:

• view or edit
• store in an archive
• remove or rename
• change access permissions
• classify into groups

This manual describes how to perform each of those tasks, and more.

1.2 Overview

The principal programs used for making lists of files that match given criteria and running commands on them are find, locate, and xargs. An additional command, updatedb, is used by system administrators to create databases for locate to use.

find searches for files in a directory hierarchy and prints information about the files it found. It is run like this:

find [file…] [expression]

Here is a typical use of find. This example prints the names of all files in the directory tree rooted in ‘/usr/src’ whose name ends with ‘.c’ and that are larger than 100 Kilobytes.

find /usr/src -name '*.c' -size +100k -print

locate searches special file name databases for file names that match patterns. The system administrator runs the updatedb program to create the databases. locate is run like this:

locate [option…] pattern…

This example prints the names of all files in the default file name database whose name ends with ‘Makefile’ or ‘makefile’. Which file names are stored in the database depends on how the system administrator ran updatedb.

locate '*[Mm]akefile'

The name xargs, pronounced EX-args, means “combine arguments.” xargs builds and executes command lines by gathering together arguments it reads on the standard input. Most often, these arguments are lists of file names generated by find. xargs is run like this:

xargs [option…] [command [initial-arguments]]

The following command searches the files listed in the file ‘file-list’ and prints all of the lines in them that contain the word ‘typedef’.

xargs grep typedef < file-list

1.3 find Expressions

The expression that find uses to select files consists of one or more primaries, each of which is a separate command line argument to find. find evaluates the expression each time it processes a file. An expression can contain any of the following types of primaries:

options

affect overall operation rather than the processing of a specific file;

tests

return a true or false value, depending on the file’s attributes;

actions

have side effects and return a true or false value; and

operators

connect the other arguments and affect when and whether they are evaluated.

You can omit the operator between two primaries; it defaults to ‘-and’. See section Combining Primaries With Operators, for ways to connect primaries into more complex expressions. If the expression contains no actions other than ‘-prune’, ‘-print’ is performed on all files for which the entire expression is true (see section Print File Name).

Options take effect immediately, rather than being evaluated for each file when their place in the expression is reached. Therefore, for clarity, it is best to place them at the beginning of the expression.

Many of the primaries take arguments, which immediately follow them in the next command line argument to find. Some arguments are file names, patterns, or other strings; others are numbers. Numeric arguments can be specified as

+n

for greater than n,

-n

for less than n,

n

for exactly n.

2 Finding Files

By default, find prints to the standard output the names of the files that match the given criteria. See section Actions, for how to get more information about the matching files.

2.1 Name

Here are ways to search for files whose name matches a certain pattern. See section Shell Pattern Matching, for a description of the pattern arguments to these tests.

Each of these tests has a case-sensitive version and a case-insensitive version, whose name begins with ‘i’. In a case-insensitive comparison, the patterns ‘fo*’ and ‘F??’ match the file names ‘Foo’, ‘FOO’, ‘foo’, ‘fOo’, etc.

2.1.1 Base Name Patterns

Test: -name pattern

Test: -iname pattern

True if the base of the file name (the path with the leading directories removed) matches shell pattern pattern. For ‘-iname’, the match is case-insensitive. To ignore a whole directory tree, use ‘-prune’ (see section Directories). As an example, to find Texinfo source files in ‘/usr/local/doc’:

find /usr/local/doc -name '*.texi'

2.1.2 Full Name Patterns

Test: -path pattern

Test: -ipath pattern

True if the entire file name, starting with the command line argument under which the file was found, matches shell pattern pattern. For ‘-ipath’, the match is case-insensitive. To ignore a whole directory tree, use ‘-prune’ rather than checking every file in the tree (see section Directories).

Test: -regex expr

Test: -iregex expr

True if the entire file name matches regular expression expr. This is a match on the whole path, not a search. For example, to match a file named ‘./fubar3’, you can use the regular expression ‘.*bar.’ or ‘.*b.*3’, but not ‘b.*r3’. See Syntax of Regular Expressions in The GNU Emacs Manual, for a description of the syntax of regular expressions. For ‘-iregex’, the match is case-insensitive.

2.1.3 Fast Full Name Search

To search for files by name without having to actually scan the directories on the disk (which can be slow), you can use the locate program. For each shell pattern you give it, locate searches one or more databases of file names and displays the file names that contain the pattern. See section Shell Pattern Matching, for details about shell patterns.

If a pattern is a plain string—it contains no metacharacters—locate displays all file names in the database that contain that string. If a pattern contains metacharacters, locate only displays file names that match the pattern exactly. As a result, patterns that contain metacharacters should usually begin with a ‘*’, and will most often end with one as well. The exceptions are patterns that are intended to explicitly match the beginning or end of a file name.

The command

locate pattern

is almost equivalent to

find directories -name pattern

where directories are the directories for which the file name databases contain information. The differences are that the locate information might be out of date, and that locate handles wildcards in the pattern slightly differently than find (see section Shell Pattern Matching).

The file name databases contain lists of files that were on the system when the databases were last updated. The system administrator can choose the file name of the default database, the frequency with which the databases are updated, and the directories for which they contain entries.

Here is how to select which file name databases locate searches. The default is system-dependent.

--database=path

-d path

Instead of searching the default file name database, search the file name databases in path, which is a colon-separated list of database file names. You can also use the environment variable LOCATE_PATH to set the list of database files to search. The option overrides the environment variable if both are used.

2.1.4 Shell Pattern Matching

find and locate can compare file names, or parts of file names, to shell patterns. A shell pattern is a string that may contain the following special characters, which are known as wildcards or metacharacters.

You must quote patterns that contain metacharacters to prevent the shell from expanding them itself. Double and single quotes both work; so does escaping with a backslash.

*

Matches any zero or more characters.

?

Matches any one character.

[string]

Matches exactly one character that is a member of the string string. This is called a character class. As a shorthand, string may contain ranges, which consist of two characters with a dash between them. For example, the class ‘[a-z0-9_]’ matches a lowercase letter, a number, or an underscore. You can negate a class by placing a ‘!’ or ‘^’ immediately after the opening bracket. Thus, ‘[^A-Z@]’ matches any character except an uppercase letter or an at sign.

\

Removes the special meaning of the character that follows it. This works even in character classes.

In the find tests that do shell pattern matching (‘-name’, ‘-path’, etc.), wildcards in the pattern do not match a ‘.’ at the beginning of a file name. This is not the case for locate. Thus, ‘find -name '*macs'’ does not match a file named ‘.emacs’, but ‘locate '*macs'’ does.

Slash characters have no special significance in the shell pattern matching that find and locate do, unlike in the shell, in which wildcards do not match them. Therefore, a pattern ‘foo*bar’ can match a file name ‘foo3/bar’, and a pattern ‘./sr*sc’ can match a file name ‘./src/misc’.

2.2 Links

There are two ways that files can be linked together. Symbolic links are a special type of file whose contents are a portion of the name of another file. Hard links are multiple directory entries for one file; the file names all have the same index node (inode) number on the disk.

2.2.1 Symbolic Links

Test: -lname pattern

Test: -ilname pattern

True if the file is a symbolic link whose contents match shell pattern pattern. For ‘-ilname’, the match is case-insensitive. See section Shell Pattern Matching, for details about the pattern argument. So, to list any symbolic links to ‘sysdep.c’ in the current directory and its subdirectories, you can do:

find . -lname '*sysdep.c'

Option: -follow

Dereference symbolic links. The following differences in behavior occur when this option is given:

• find follows symbolic links to directories when searching directory trees.
• ‘-lname’ and ‘-ilname’ always return false.
• ‘-type’ reports the types of the files that symbolic links point to.
• Implies ‘-noleaf’ (see section Directories).

2.2.2 Hard Links

To find hard links, first get the inode number of the file whose links you want to find. You can learn a file’s inode number and the number of links to it by running ‘ls -i’ or ‘find -ls’. If the file has more than one link, you can search for the other links by passing that inode number to ‘-inum’. Add the ‘-xdev’ option if you are starting the search at a directory that has other filesystems mounted on it, such as ‘/usr’ on many systems. Doing this saves needless searching, since hard links to a file must be on the same filesystem. See section Filesystems.

Test: -inum n

File has inode number n.

You can also search for files that have a certain number of links, with ‘-links’. Directories normally have at least two hard links; their ‘.’ entry is the second one. If they have subdirectories, each of those also has a hard link called ‘..’ to its parent directory.

Test: -links n

File has n hard links.

2.3 Time

Each file has three time stamps, which record the last time that certain operations were performed on the file:

1. access (read the file’s contents)
2. change the status (modify the file or its attributes)
3. modify (change the file’s contents)

You can search for files whose time stamps are within a certain age range, or compare them to other time stamps.

2.3.1 Age Ranges

These tests are mainly useful with ranges (‘+n’ and ‘-n’).

Test: -atime n

Test: -ctime n

Test: -mtime n

True if the file was last accessed (or its status changed, or it was modified) n*24 hours ago.

Test: -amin n

Test: -cmin n

Test: -mmin n

True if the file was last accessed (or its status changed, or it was modified) n minutes ago. These tests provide finer granularity of measurement than ‘-atime’ et al. For example, to list files in ‘/u/bill’ that were last read from 2 to 6 hours ago:

find /u/bill -amin +2 -amin -6

Option: -daystart

Measure times from the beginning of today rather than from 24 hours ago. So, to list the regular files in your home directory that were modified yesterday, do

find ~ -daystart -type f -mtime 1

2.3.2 Comparing Timestamps

As an alternative to comparing timestamps to the current time, you can compare them to another file’s timestamp. That file’s timestamp could be updated by another program when some event occurs. Or you could set it to a particular fixed date using the touch command. For example, to list files in ‘/usr’ modified after February 1 of the current year:

touch -t 02010000 /tmp/stamp$$
find /usr -newer /tmp/stamp$$
rm -f /tmp/stamp$$

Test: -anewer file

Test: -cnewer file

Test: -newer file

True if the file was last accessed (or its status changed, or it was modified) more recently than file was modified. These tests are affected by ‘-follow’ only if ‘-follow’ comes before them on the command line. See section Symbolic Links, for more information on ‘-follow’. As an example, to list any files modified since ‘/bin/sh’ was last modified:

find . -newer /bin/sh

Test: -used n

True if the file was last accessed n days after its status was last changed. Useful for finding files that are not being used, and could perhaps be archived or removed to save disk space.

2.4 Size

Test: -size n[bckw]

True if the file uses n units of space, rounding up. The units are 512-byte blocks by default, but they can be changed by adding a one-character suffix to n:

b

512-byte blocks

c

bytes

k

kilobytes (1024 bytes)

w

2-byte words

The size does not count indirect blocks, but it does count blocks in sparse files that are not actually allocated.

Test: -empty

True if the file is empty and is either a regular file or a directory. This might make it a good candidate for deletion. This test is useful with ‘-depth’ (see section Directories) and ‘-exec rm -rf '{}' ';'’ (see section Single File).

2.5 Type

Test: -type c

True if the file is of type c:

b

block (buffered) special

c

character (unbuffered) special

d

directory

p

named pipe (FIFO)

f

regular file

l

symbolic link

s

socket

Test: -xtype c

The same as ‘-type’ unless the file is a symbolic link. For symbolic links: if ‘-follow’ has not been given, true if the file is a link to a file of type c; if ‘-follow’ has been given, true if c is ‘l’. In other words, for symbolic links, ‘-xtype’ checks the type of the file that ‘-type’ does not check. See section Symbolic Links, for more information on ‘-follow’.

2.6 Owner

Test: -user uname

Test: -group gname

True if the file is owned by user uname (belongs to group gname). A numeric ID is allowed.

Test: -uid n

Test: -gid n

True if the file’s numeric user ID (group ID) is n. These tests support ranges (‘+n’ and ‘-n’), unlike ‘-user’ and ‘-group’.

Test: -nouser

Test: -nogroup

True if no user corresponds to the file’s numeric user ID (no group corresponds to the numeric group ID). These cases usually mean that the files belonged to users who have since been removed from the system. You probably should change the ownership of such files to an existing user or group, using the chown or chgrp program.

2.7 Permissions

See section File Permissions, for information on how file permissions are structured and how to specify them.

Test: -perm mode

True if the file’s permissions are exactly mode (which can be numeric or symbolic). Symbolic modes use mode 0 as a point of departure. If mode starts with ‘-’, true if all of the permissions set in mode are set for the file; permissions not set in mode are ignored. If mode starts with ‘+’, true if any of the permissions set in mode are set for the file; permissions not set in mode are ignored.

2.8 Contents

To search for files based on their contents, you can use the grep program. For example, to find out which C source files in the current directory contain the string ‘thing’, you can do:

grep -l thing *.[ch]

If you also want to search for the string in files in subdirectories, you can combine grep with find and xargs, like this:

find . -name '*.[ch]' | xargs grep -l thing

The ‘-l’ option causes grep to print only the names of files that contain the string, rather than the lines that contain it. The string argument (‘thing’) is actually a regular expression, so it can contain metacharacters. This method can be refined a little by using the ‘-r’ option to make xargs not run grep if find produces no output, and using the find action ‘-print0’ and the xargs option ‘-0’ to avoid misinterpreting files whose names contain spaces:

find . -name '*.[ch]' -print0 | xargs -r -0 grep -l thing

For a fuller treatment of finding files whose contents match a pattern, see the manual page for grep.

2.9 Directories

Here is how to control which directories find searches, and how it searches them. These two options allow you to process a horizontal slice of a directory tree.

Option: -maxdepth levels

Descend at most levels (a non-negative integer) levels of directories below the command line arguments. ‘-maxdepth 0’ means only apply the tests and actions to the command line arguments.

Option: -mindepth levels

Do not apply any tests or actions at levels less than levels (a non-negative integer). ‘-mindepth 1’ means process all files except the command line arguments.

Option: -depth

Process each directory’s contents before the directory itself. Doing this is a good idea when producing lists of files to archive with cpio or tar. If a directory does not have write permission for its owner, its contents can still be restored from the archive since the directory’s permissions are restored after its contents.

Action: -prune

If ‘-depth’ is not given, true; do not descend the current directory. If ‘-depth’ is given, false; no effect. ‘-prune’ only affects tests and actions that come after it in the expression, not those that come before.

For example, to skip the directory ‘src/emacs’ and all files and directories under it, and print the names of the other files found:

find . -path './src/emacs' -prune -o -print

Option: -noleaf

Do not optimize by assuming that directories contain 2 fewer subdirectories than their hard link count. This option is needed when searching filesystems that do not follow the Unix directory-link convention, such as CD-ROM or MS-DOS filesystems or AFS volume mount points. Each directory on a normal Unix filesystem has at least 2 hard links: its name and its ‘.’ entry. Additionally, its subdirectories (if any) each have a ‘..’ entry linked to that directory. When find is examining a directory, after it has statted 2 fewer subdirectories than the directory’s link count, it knows that the rest of the entries in the directory are non-directories (leaf files in the directory tree). If only the files’ names need to be examined, there is no need to stat them; this gives a significant increase in search speed.

2.10 Filesystems

A filesystem is a section of a disk, either on the local host or mounted from a remote host over a network. Searching network filesystems can be slow, so it is common to make find avoid them.

There are two ways to avoid searching certain filesystems. One way is to tell find to only search one filesystem:

Option: -xdev

Option: -mount

Don’t descend directories on other filesystems. These options are synonyms.

The other way is to check the type of filesystem each file is on, and not descend directories that are on undesirable filesystem types:

Test: -fstype type

True if the file is on a filesystem of type type. The valid filesystem types vary among different versions of Unix; an incomplete list of filesystem types that are accepted on some version of Unix or another is:

ufs 4.2 4.3 nfs tmp mfs S51K S52K

You can use ‘-printf’ with the ‘%F’ directive to see the types of your filesystems. See section Print File Information. ‘-fstype’ is usually used with ‘-prune’ to avoid searching remote filesystems (see section Directories).

2.11 Combining Primaries With Operators

Operators build a complex expression from tests and actions. The operators are, in order of decreasing precedence:

( expr )

Force precedence. True if expr is true.

! expr

-not expr

True if expr is false.

expr1 expr2

expr1 -a expr2

expr1 -and expr2

And; expr2 is not evaluated if expr1 is false.

expr1 -o expr2

expr1 -or expr2

Or; expr2 is not evaluated if expr1 is true.

expr1 , expr2

List; both expr1 and expr2 are always evaluated. True if expr2 is true. The value of expr1 is discarded. This operator lets you do multiple independent operations on one traversal, without depending on whether other operations succeeded.

find searches the directory tree rooted at each file name by evaluating the expression from left to right, according to the rules of precedence, until the outcome is known (the left hand side is false for ‘-and’, true for ‘-or’), at which point find moves on to the next file name.

There are two other tests that can be useful in complex expressions:

Test: -true

Always true.

Test: -false

Always false.

3 Actions

There are several ways you can print information about the files that match the criteria you gave in the find expression. You can print the information either to the standard output or to a file that you name. You can also execute commands that have the file names as arguments. You can use those commands as further filters to select files.

3.1 Print File Name

Action: -print

True; print the full file name on the standard output, followed by a newline.

Action: -fprint file

True; print the full file name into file file, followed by a newline. If file does not exist when find is run, it is created; if it does exist, it is truncated to 0 bytes. The file names ‘/dev/stdout’ and ‘/dev/stderr’ are handled specially; they refer to the standard output and standard error output, respectively.

3.2 Print File Information

Action: -ls

True; list the current file in ‘ls -dils’ format on the standard output. The output looks like this:

204744   17 -rw-r--r--   1 djm      staff       17337 Nov  2  1992 ./lwall-quotes

The fields are:

1. The inode number of the file. See section Hard Links, for how to find files based on their inode number.
2. the number of blocks in the file. The block counts are of 1K blocks, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used. See section Size, for how to find files based on their size.
3. The file’s type and permissions. The type is shown as a dash for a regular file; for other file types, a letter like for ‘-type’ is used (see section Type). The permissions are read, write, and execute for the file’s owner, its group, and other users, respectively; a dash means the permission is not granted. See section File Permissions, for more details about file permissions. See section Permissions, for how to find files based on their permissions.
4. The number of hard links to the file.
5. The user who owns the file.
6. The file’s group.
7. The file’s size in bytes.
8. The date the file was last modified.
9. The file’s name. ‘-ls’ quotes non-printable characters in the file names using C-like backslash escapes.

Action: -fls file

True; like ‘-ls’ but write to file like ‘-fprint’ (see section Print File Name).

Action: -printf format

True; print format on the standard output, interpreting ‘\’ escapes and ‘%’ directives. Field widths and precisions can be specified as with the printf C function. Unlike ‘-print’, ‘-printf’ does not add a newline at the end of the string.

Action: -fprintf file format

True; like ‘-printf’ but write to file like ‘-fprint’ (see section Print File Name).

3.2.1 Escapes

The escapes that ‘-printf’ and ‘-fprintf’ recognize are:

\a

Alarm bell.

\b

Backspace.

\c

Stop printing from this format immediately and flush the output.

\f

Form feed.

\n

Newline.

\r

Carriage return.

\t

Horizontal tab.

\v

Vertical tab.

\\

A literal backslash (‘\’).

A ‘\’ character followed by any other character is treated as an ordinary character, so they both are printed, and a warning message is printed to the standard error output (because it was probably a typo).

3.2.2 Format Directives

‘-printf’ and ‘-fprintf’ support the following format directives to print information about the file being processed. Unlike the C printf function, they do not support field width specifiers.

‘%%’ is a literal percent sign. A ‘%’ character followed by any other character is discarded (but the other character is printed), and a warning message is printed to the standard error output (because it was probably a typo).

3.2.2.1 Name Directives

%p

File’s name.

%f

File’s name with any leading directories removed (only the last element).

%h

Leading directories of file’s name (all but the last element and the slash before it).

%P

File’s name with the name of the command line argument under which it was found removed from the beginning.

%H

Command line argument under which file was found.

3.2.2.2 Ownership Directives

%g

File’s group name, or numeric group ID if the group has no name.

%G

File’s numeric group ID.

%u

File’s user name, or numeric user ID if the user has no name.

%U

File’s numeric user ID.

%m

File’s permissions (in octal).

3.2.2.3 Size Directives

%k

File’s size in 1K blocks (rounded up).

%b

File’s size in 512-byte blocks (rounded up).

%s

File’s size in bytes.

3.2.2.4 Location Directives

%d

File’s depth in the directory tree; files named on the command line have a depth of 0.

%F

Type of the filesystem the file is on; this value can be used for ‘-fstype’ (see section Directories).

%l

Object of symbolic link (empty string if file is not a symbolic link).

%i

File’s inode number (in decimal).

%n

Number of hard links to file.

3.2.2.5 Time Directives

Some of these directives use the C ctime function. Its output depends on the current locale, but it typically looks like

Wed Nov  2 00:42:36 1994

%a

File’s last access time in the format returned by the C ctime function.

%Ak

File’s last access time in the format specified by k (see section Time Formats).

%c

File’s last status change time in the format returned by the C ctime function.

%Ck

File’s last status change time in the format specified by k (see section Time Formats).

%t

File’s last modification time in the format returned by the C ctime function.

%Tk

File’s last modification time in the format specified by k (see section Time Formats).

3.2.3 Time Formats

Below are the formats for the directives ‘%A’, ‘%C’, and ‘%T’, which print the file’s timestamps. Some of these formats might not be available on all systems, due to differences in the C strftime function between systems.

3.2.3.1 Time Components

The following format directives print single components of the time.

H

hour (00..23)

I

hour (01..12)

k

hour ( 0..23)

l

hour ( 1..12)

p

locale’s AM or PM

Z

time zone (e.g., EDT), or nothing if no time zone is determinable

M

minute (00..59)

S

second (00..61)

@

seconds since Jan. 1, 1970, 00:00 GMT.

3.2.3.2 Date Components

The following format directives print single components of the date.

a

locale’s abbreviated weekday name (Sun..Sat)

A

locale’s full weekday name, variable length (Sunday..Saturday)

b

h

locale’s abbreviated month name (Jan..Dec)

B

locale’s full month name, variable length (January..December)

m

month (01..12)

d

day of month (01..31)

w

day of week (0..6)

j

day of year (001..366)

U

week number of year with Sunday as first day of week (00..53)

W

week number of year with Monday as first day of week (00..53)

Y

year (1970…)

y

last two digits of year (00..99)

3.2.3.3 Combined Time Formats

The following format directives print combinations of time and date components.

r

time, 12-hour (hh:mm:ss [AP]M)

T

time, 24-hour (hh:mm:ss)

X

locale’s time representation (H:M:S)

c

locale’s date and time (Sat Nov 04 12:02:33 EST 1989)

D

date (mm/dd/yy)

x

locale’s date representation (mm/dd/yy)

3.3 Run Commands

You can use the list of file names created by find or locate as arguments to other commands. In this way you can perform arbitrary actions on the files.

3.3.1 Single File

Here is how to run a command on one file at a time.

Action: -exec command ;

Execute command; true if 0 status is returned. find takes all arguments after ‘-exec’ to be part of the command until an argument consisting of ‘;’ is reached. It replaces the string ‘{}’ by the current file name being processed everywhere it occurs in the command. Both of these constructions need to be escaped (with a ‘\’) or quoted to protect them from expansion by the shell. The command is executed in the directory in which find was run.

For example, to compare each C header file in the current directory with the file ‘/tmp/master’:

find . -name '*.h' -exec diff -u '{}' /tmp/master ';'

3.3.2 Multiple Files

Sometimes you need to process files alone. But when you don’t, it is faster to run a command on as many files as possible at a time, rather than once per file. Doing this saves on the time it takes to start up the command each time.

To run a command on more than one file at once, use the xargs command, which is invoked like this:

xargs [option…] [command [initial-arguments]]

xargs reads arguments from the standard input, delimited by blanks (which can be protected with double or single quotes or a backslash) or newlines. It executes the command (default is ‘/bin/echo’) one or more times with any initial-arguments followed by arguments read from standard input. Blank lines on the standard input are ignored.

Instead of blank-delimited names, it is safer to use ‘find -print0’ or ‘find -fprint0’ and process the output by giving the ‘-0’ or ‘--null’ option to GNU xargs, GNU tar, GNU cpio, or perl.

You can use shell command substitution (backquotes) to process a list of arguments, like this:

grep -l sprintf `find $HOME -name '*.c' -print`

However, that method produces an error if the length of the ‘.c’ file names exceeds the operating system’s command-line length limit. xargs avoids that problem by running the command as many times as necessary without exceeding the limit:

find $HOME -name '*.c' -print | grep -l sprintf

However, if the command needs to have its standard input be a terminal (less, for example), you have to use the shell command substitution method.

3.3.2.1 Unsafe File Name Handling

Because file names can contain quotes, backslashes, blank characters, and even newlines, it is not safe to process them using xargs in its default mode of operation. But since most files’ names do not contain blanks, this problem occurs only infrequently. If you are only searching through files that you know have safe names, then you need not be concerned about it.

In many applications, if xargs botches processing a file because its name contains special characters, some data might be lost. The importance of this problem depends on the importance of the data and whether anyone notices the loss soon enough to correct it. However, here is an extreme example of the problems that using blank-delimited names can cause. If the following command is run daily from cron, then any user can remove any file on the system:

find / -name '#*' -atime +7 -print | xargs rm

For example, you could do something like this:

eg$ echo > '#
vmunix'

and then cron would delete ‘/vmunix’, if it ran xargs with ‘/’ as its current directory.

To delete other files, for example ‘/u/joeuser/.plan’, you could do this:

eg$ mkdir '#
'
eg$ cd '#
'
eg$ mkdir u u/joeuser u/joeuser/.plan'
'
eg$ echo > u/joeuser/.plan'
/#foo'
eg$ cd ..
eg$ find . -name '#*' -print | xargs echo
./# ./# /u/joeuser/.plan /#foo

3.3.2.2 Safe File Name Handling

Here is how to make find output file names so that they can be used by other programs without being mangled or misinterpreted. You can process file names generated this way by giving the ‘-0’ or ‘--null’ option to GNU xargs, GNU tar, GNU cpio, or perl.

Action: -print0

True; print the full file name on the standard output, followed by a null character.

Action: -fprint0 file

True; like ‘-print0’ but write to file like ‘-fprint’ (see section Print File Name).

3.3.2.3 Limiting Command Size

xargs gives you control over how many arguments it passes to the command each time it executes it. By default, it uses up to ARG_MAX - 2k, or 20k, whichever is smaller, characters per command. It uses as many lines and arguments as fit within that limit. The following options modify those values.

--no-run-if-empty

-r

If the standard input does not contain any nonblanks, do not run the command. By default, the command is run once even if there is no input.

--max-lines[=max-lines]

-l[max-lines]

Use at most max-lines nonblank input lines per command line; max-lines defaults to 1 if omitted. Trailing blanks cause an input line to be logically continued on the next input line, for the purpose of counting the lines. Implies ‘-x’.

--max-args=max-args

-n max-args

Use at most max-args arguments per command line. Fewer than max-args arguments will be used if the size (see the ‘-s’ option) is exceeded, unless the ‘-x’ option is given, in which case xargs will exit.

--max-chars=max-chars

-s max-chars

Use at most max-chars characters per command line, including the command and initial arguments and the terminating nulls at the ends of the argument strings.

--max-procs=max-procs

-P max-procs

Run up to max-procs processes at a time; the default is 1. If max-procs is 0, xargs will run as many processes as possible at a time. Use the ‘-n’, ‘-s’, or ‘-l’ option with ‘-P’; otherwise chances are that the command will be run only once.

3.3.2.4 Interspersing File Names

xargs can insert the name of the file it is processing between arguments you give for the command. Unless you also give options to limit the command size (see section Limiting Command Size), this mode of operation is equivalent to ‘find -exec’ (see section Single File).

--replace[=replace-str]

-i[replace-str]

Replace occurences of replace-str in the initial arguments with names read from standard input. Also, unquoted blanks do not terminate arguments. If replace-str is omitted, it defaults to ‘{}’ (like for ‘find -exec’). Implies ‘-x’ and ‘-l 1’. As an example, to sort each file the ‘bills’ directory, leaving the output in that file name with ‘.sorted’ appended, you could do:

find bills -type f | xargs -iXX sort -o XX.sorted XX

The equivalent command using ‘find -exec’ is:

find bills -type f -exec sort -o '{}.sorted' '{}' ';'

3.3.3 Querying

To ask the user whether to execute a command on a single file, you can use the find primary ‘-ok’ instead of ‘-exec’:

Action: -ok command ;

Like ‘-exec’ (see section Single File), but ask the user first (on the standard input); if the response does not start with ‘y’ or ‘Y’, do not run the command, and return false.

When processing multiple files with a single command, to query the user you give xargs the following option. When using this option, you might find it useful to control the number of files processed per invocation of the command (see section Limiting Command Size).

--interactive

-p

Prompt the user about whether to run each command line and read a line from the terminal. Only run the command line if the response starts with ‘y’ or ‘Y’. Implies ‘-t’.

3.4 Adding Tests

You can test for file attributes that none of the find builtin tests check. To do this, use xargs to run a program that filters a list of files printed by find. If possible, use find builtin tests to pare down the list, so the program run by xargs has less work to do. The tests builtin to find will likely run faster than tests that other programs perform.

For example, here is a way to print the names of all of the unstripped binaries in the ‘/usr/local’ directory tree. Builtin tests avoid running file on files that are not regular files or are not executable.

find /usr/local -type f -perm +a=x | xargs file | 
  grep 'not stripped' | cut -d: -f1

The cut program removes everything after the file name from the output of file.

If you want to place a special test somewhere in the middle of a find expression, you can use ‘-exec’ to run a program that performs the test. Because ‘-exec’ evaluates to the exit status of the executed program, you can write a program (which can be a shell script) that tests for a special attribute and make it exit with a true (zero) or false (non-zero) status. It is a good idea to place such a special test after the builtin tests, because it starts a new process which could be avoided if a builtin test evaluates to false. Use this method only when xargs is not flexible enough, because starting one or more new processes to test each file is slower than using xargs to start one process that tests many files.

Here is a shell script called unstripped that checks whether its argument is an unstripped binary file:

#!/bin/sh
file $1 | grep 'not stripped' > /dev/null

This script relies on the fact that the shell exits with the status of the last program it executed, in this case grep. grep exits with a true status if it found any matches, false if not. Here is an example of using the script (assuming it is in your search path). It lists the stripped executables in the file ‘sbins’ and the unstripped ones in ‘ubins’.

find /usr/local -type f -perm +a=x \
  \( -exec unstripped '{}' \; -fprint ubins -o -fprint sbins \)

4 Common Tasks

The sections that follow contain some extended examples that both give a good idea of the power of these programs, and show you how to solve common real-world problems.

4.1 Viewing And Editing

To view a list of files that meet certain criteria, simply run your file viewing program with the file names as arguments. Shells substitute a command enclosed in backquotes with its output, so the whole command looks like this:

less `find /usr/include -name '*.h' | xargs grep -l mode_t`

You can edit those files by giving an editor name instead of a file viewing program.

4.2 Archiving

You can pass a list of files produced by find to a file archiving program. GNU tar and cpio can both read lists of file names from the standard input—either delimited by nulls (the safe way) or by blanks (the lazy, risky default way). To use null-delimited names, give them the ‘--null’ option. You can store a file archive in a file, write it on a tape, or send it over a network to extract on another machine.

One common use of find to archive files is to send a list of the files in a directory tree to cpio. Use ‘-depth’ so if a directory does not have write permission for its owner, its contents can still be restored from the archive since the directory’s permissions are restored after its contents. Here is an example of doing this using cpio; you could use a more complex find expression to archive only certain files.

find . -depth -print0 |
  cpio --create --null --format=crc --file=/dev/nrst0

You could restore that archive using this command:

cpio --extract --null --make-dir --unconditional \
  --preserve --file=/dev/nrst0

Here are the commands to do the same things using tar:

find . -depth -print0 |
  tar --create --null --files-from=- --file=/dev/nrst0

tar --extract --null --preserve-perm --same-owner \
  --file=/dev/nrst0

Here is an example of copying a directory from one machine to another:

find . -depth -print0 | cpio -0o -Hnewc |
  rsh other-machine "cd `pwd` && cpio -i0dum"

4.3 Cleaning Up

This section gives examples of removing unwanted files in various situations. Here is a command to remove the CVS backup files created when an update requires a merge:

find . -name '.#*' -print0 | xargs -0r rm -f

You can run this command to clean out your clutter in ‘/tmp’. You might place it in the file your shell runs when you log out (‘.bash_logout’, ‘.logout’, or ‘.zlogout’, depending on which shell you use).

find /tmp -user $LOGNAME -type f -print0 | xargs -0 -r rm -f

To remove old Emacs backup and auto-save files, you can use a command like the following. It is especially important in this case to use null-terminated file names because Emacs packages like the VM mailer often create temporary file names with spaces in them, like ‘#reply to David J. MacKenzie<1>#’.

find ~ \( -name '*~' -o -name '#*#' \) -print0 |
  xargs --no-run-if-empty --null rm -vf

Removing old files from ‘/tmp’ is commonly done from cron:

find /tmp /var/tmp -not -type d -mtime +3 -print0 |
  xargs --null --no-run-if-empty rm -f

find /tmp /var/tmp -depth -mindepth 1 -type d -empty -print0 |
  xargs --null --no-run-if-empty rmdir

The second find command above uses ‘-depth’ so it cleans out empty directories depth-first, hoping that the parents become empty and can be removed too. It uses ‘-mindepth’ to avoid removing ‘/tmp’ itself if it becomes totally empty.

4.4 Strange File Names

find can help you remove or rename a file with strange characters in its name. People are sometimes stymied by files whose names contain characters such as spaces, tabs, control characters, or characters with the high bit set. The simplest way to remove such files is:

rm -i some*pattern*that*matches*the*problem*file

rm asks you whether to remove each file matching the given pattern. If you are using an old shell, this approach might not work if the file name contains a character with the high bit set; the shell may strip it off. A more reliable way is:

find . -maxdepth 1 tests -ok rm '{}' \;

where tests uniquely identify the file. The ‘-maxdepth 1’ option prevents find from wasting time searching for the file in any subdirectories; if there are no subdirectories, you may omit it. A good way to uniquely identify the problem file is to figure out its inode number; use

ls -i

Suppose you have a file whose name contains control characters, and you have found that its inode number is 12345. This command prompts you for whether to remove it:

find . -maxdepth 1 -inum 12345 -ok rm -f '{}' \;

If you don’t want to be asked, perhaps because the file name may contain a strange character sequence that will mess up your screen when printed, then use ‘-exec’ instead of ‘-ok’.

If you want to rename the file instead, you can use mv instead of rm:

find . -maxdepth 1 -inum 12345 -ok mv '{}' new-file-name \;

4.5 Fixing Permissions

Suppose you want to make sure that everyone can write to the directories in a certain directory tree. Here is a way to find directories lacking either user or group write permission (or both), and fix their permissions:

find . -type d -not -perm -ug=w | xargs chmod ug+w

You could also reverse the operations, if you want to make sure that directories do not have world write permission.

4.6 Classifying Files

If you want to classify a set of files into several groups based on different criteria, you can use the comma operator to perform multiple independent tests on the files. Here is an example:

find / -type d \( -perm -o=w -fprint allwrite , \
  -perm -o=x -fprint allexec \)

echo "Directories that can be written to by everyone:"
cat allwrite
echo ""
echo "Directories with search permissions for everyone:"
cat allexec

find has only to make one scan through the directory tree (which is one of the most time consuming parts of its work).

5 File Name Databases

The file name databases used by locate contain lists of files that were in particular directory trees when the databases were last updated. The file name of the default database is determined when locate and updatedb are configured and installed. The frequency with which the databases are updated and the directories for which they contain entries depend on how often updatedb is run, and with which arguments.

5.1 Database Locations

There can be multiple file name databases. Users can select which databases locate searches using an environment variable or a command line option. The system administrator can choose the file name of the default database, the frequency with which the databases are updated, and the directories for which they contain entries. File name databases are updated by running the updatedb program, typically nightly.

In networked environments, it often makes sense to build a database at the root of each filesystem, containing the entries for that filesystem. updatedb is then run for each filesystem on the fileserver where that filesystem is on a local disk, to prevent thrashing the network. Here are the options to updatedb to select which directories each database contains entries for:

--localpaths='path…'

Non-network directories to put in the database. Default is ‘/’.

--netpaths='path…'

Network (NFS, AFS, RFS, etc.) directories to put in the database. Default is none.

--prunepaths='path…'

Directories to not put in the database, which would otherwise be. Default is ‘/tmp /usr/tmp /var/tmp /afs’.

--output=dbfile

The database file to build. Default is system-dependent, but typically ‘/usr/local/var/locatedb’.

--netuser=user

The user to search network directories as, using su. Default is daemon.

5.2 Database Formats

The file name databases contain lists of files that were in particular directory trees when the databases were last updated. The file name database format changed starting with GNU locate version 4.0 to allow machines with diffent byte orderings to share the databases. The new GNU locate can read both the old and new database formats. However, old versions of locate and find produce incorrect results if given a new-format database.

5.2.1 New Database Format

updatedb runs a program called frcode to front-compress the list of file names, which reduces the database size by a factor of 4 to 5. Front-compression (also known as incremental encoding) works as follows.

The database entries are a sorted list (case-insensitively, for users’ convenience). Since the list is sorted, each entry is likely to share a prefix (initial string) with the previous entry. Each database entry begins with an offset-differential count byte, which is the additional number of characters of prefix of the preceding entry to use beyond the number that the preceding entry is using of its predecessor. (The counts can be negative.) Following the count is a null-terminated ASCII remainder—the part of the name that follows the shared prefix.

If the offset-differential count is larger than can be stored in a byte (+/-127), the byte has the value 0x80 and the count follows in a 2-byte word, with the high byte first (network byte order).

Every database begins with a dummy entry for a file called ‘LOCATE02’, which locate checks for to ensure that the database file has the correct format; it ignores the entry in doing the search.

Databases can not be concatenated together, even if the first (dummy) entry is trimmed from all but the first database. This is because the offset-differential count in the first entry of the second and following databases will be wrong.

5.2.2 Sample Database

Sample input to frcode:

/usr/src
/usr/src/cmd/aardvark.c
/usr/src/cmd/armadillo.c
/usr/tmp/zoo

Length of the longest prefix of the preceding entry to share:

0 /usr/src
8 /cmd/aardvark.c
14 rmadillo.c
5 tmp/zoo

Output from frcode, with trailing nulls changed to newlines and count bytes made printable:

0 LOCATE02
0 /usr/src
8 /cmd/aardvark.c
6 rmadillo.c
-9 tmp/zoo

(6 = 14 - 8, and -9 = 5 - 14)

5.2.3 Old Database Format

The old database format is used by Unix locate and find programs and earlier releases of the GNU ones. updatedb produces this format if given the ‘--old-format’ option.

updatedb runs programs called bigram and code to produce old-format databases. The old format differs from the new one in the following ways. Instead of each entry starting with an offset-differential count byte and ending with a null, byte values from 0 through 28 indicate offset-differential counts from -14 through 14. The byte value indicating that a long offset-differential count follows is 0x1e (30), not 0x80. The long counts are stored in host byte order, which is not necessarily network byte order, and host integer word size, which is usually 4 bytes. They also represent a count 14 less than their value. The database lines have no termination byte; the start of the next line is indicated by its first byte having a value <= 30.

In addition, instead of starting with a dummy entry, the old database format starts with a 256 byte table containing the 128 most common bigrams in the file list. A bigram is a pair of adjacent bytes. Bytes in the database that have the high bit set are indexes (with the high bit cleared) into the bigram table. The bigram and offset-differential count coding makes these databases 20-25% smaller than the new format, but makes them not 8-bit clean. Any byte in a file name that is in the ranges used for the special codes is replaced in the database by a question mark, which not coincidentally is the shell wildcard to match a single character.

6 File Permissions

7 Reference

Below are summaries of the command line syntax for the programs discussed in this manual.

7.1 Invoking find

find [file…] [expression]

find searches the directory tree rooted at each file name file by evaluating the expression on each file it finds in the tree.

find considers the first argument that begins with ‘-’, ‘(’, ‘)’, ‘,’, or ‘!’ to be the beginning of the expression; any arguments before it are paths to search, and any arguments after it are the rest of the expression. If no paths are given, the current directory is used. If no expression is given, the expression ‘-print’ is used.

find exits with status 0 if all files are processed successfully, greater than 0 if errors occur.

See section find Primary Index, for a summary of all of the tests, actions, and options that the expression can contain.

find also recognizes two options for administrative use:

--help

Print a summary of the command-line argument format and exit.

--version

Print the version number of find and exit.

7.2 Invoking locate

locate [option…] pattern…

--database=path

-d path

Instead of searching the default file name database, search the file name databases in path, which is a colon-separated list of database file names. You can also use the environment variable LOCATE_PATH to set the list of database files to search. The option overrides the environment variable if both are used.

--help

Print a summary of the options to locate and exit.

--version

Print the version number of locate and exit.

7.3 Invoking updatedb

updatedb [option…]

--localpaths='path…'

Non-network directories to put in the database. Default is ‘/’.

--netpaths='path…'

Network (NFS, AFS, RFS, etc.) directories to put in the database. Default is none.

--prunepaths='path…'

Directories to not put in the database, which would otherwise be. Default is ‘/tmp /usr/tmp /var/tmp /afs’.

--output=dbfile

The database file to build. Default is system-dependent, but typically ‘/usr/local/var/locatedb’.

--netuser=user

The user to search network directories as, using su(1). Default is daemon.

7.4 Invoking xargs

xargs [option…] [command [initial-arguments]]

xargs exits with the following status:

0

if it succeeds

123

if any invocation of the command exited with status 1-125

124

if the command exited with status 255

125

if the command is killed by a signal

126

if the command cannot be run

127

if the command is not found

1

if some other error occurred.

--null

-0

Input filenames are terminated by a null character instead of by whitespace, and the quotes and backslash are not special (every character is taken literally). Disables the end of file string, which is treated like any other argument.

--eof[=eof-str]

-e[eof-str]

Set the end of file string to eof-str. If the end of file string occurs as a line of input, the rest of the input is ignored. If eof-str is omitted, there is no end of file string. If this option is not given, the end of file string defaults to ‘_’.

--help

Print a summary of the options to xargs and exit.

--replace[=replace-str]

-i[replace-str]

Replace occurences of replace-str in the initial arguments with names read from standard input. Also, unquoted blanks do not terminate arguments. If replace-str is omitted, it defaults to ‘{}’ (like for ‘find -exec’). Implies ‘-x’ and ‘-l 1’.

--max-lines[=max-lines]

-l[max-lines]

Use at most max-lines nonblank input lines per command line; max-lines defaults to 1 if omitted. Trailing blanks cause an input line to be logically continued on the next input line, for the purpose of counting the lines. Implies ‘-x’.

--max-args=max-args

-n max-args

Use at most max-args arguments per command line. Fewer than max-args arguments will be used if the size (see the ‘-s’ option) is exceeded, unless the ‘-x’ option is given, in which case xargs will exit.

--interactive

-p

Prompt the user about whether to run each command line and read a line from the terminal. Only run the command line if the response starts with ‘y’ or ‘Y’. Implies ‘-t’.

--no-run-if-empty

-r

If the standard input does not contain any nonblanks, do not run the command. By default, the command is run once even if there is no input.

--max-chars=max-chars

-s max-chars

Use at most max-chars characters per command line, including the command and initial arguments and the terminating nulls at the ends of the argument strings.

--verbose

-t

Print the command line on the standard error output before executing it.

--version

Print the version number of xargs and exit.

--exit

-x

Exit if the size (see the -s option) is exceeded.

--max-procs=max-procs

-P max-procs

Run up to max-procs processes at a time; the default is 1. If max-procs is 0, xargs will run as many processes as possible at a time.

find Primary Index

This is a list of all of the primaries (tests, actions, and options) that make up find expressions for selecting files. See section find Expressions, for more information on expressions.

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