find version 4.1
find Primary Index
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'.
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:
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:
This manual describes how to perform each of those tasks, and more.
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
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:
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
-n
n
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.
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.
find /usr/local/doc -name '*.texi'
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
LOCATE_PATH to set the list of database files to search. The
option overrides the environment variable if both are used.
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.
*
?
[string]
\
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'.
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.
find . -lname '*sysdep.c'
find follows symbolic links to directories when searching
directory trees.
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.
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.
Each file has three time stamps, which record the last time that certain operations were performed on the file:
You can search for files whose time stamps are within a certain age range, or compare them to other time stamps.
These tests are mainly useful with ranges (`+n' and `-n').
find /u/bill -amin +2 -amin -6
find ~ -daystart -type f -mtime 1
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$$
find . -newer /bin/sh
b
c
k
w
The size does not count indirect blocks, but it does count blocks in sparse files that are not actually allocated.
b
c
d
p
f
l
s
chown or chgrp program.
See section File Permissions, for information on how file permissions are structured and how to specify them.
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.
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.
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.
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
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.
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:
The other way is to check the type of filesystem each file is on, and not descend directories that are on undesirable filesystem types:
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).
Operators build a complex expression from tests and actions. The operators are, in order of decreasing precedence:
( expr )
! expr
-not expr
expr1 expr2
expr1 -a expr2
expr1 -and expr2
expr1 -o expr2
expr1 -or expr2
expr1 , expr2
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:
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.
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.
204744 17 -rw-r--r-- 1 djm staff 17337 Nov 2 1992 ./lwall-quotes
The fields are:
POSIXLY_CORRECT is set, in which
case 512-byte blocks are used. See section Size, for how to find files based
on their size.
printf C function. Unlike `-print',
`-printf' does not add a newline at the end of the string.
The escapes that `-printf' and `-fprintf' recognize are:
\a
\b
\c
\f
\n
\r
\t
\v
\\
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).
`-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).
%p
%f
%h
%P
%H
%g
%G
%u
%U
%m
%k
%b
%s
%d
%F
%l
%i
%n
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
ctime function.
%Ak
%c
ctime
function.
%Ck
%t
ctime
function.
%Tk
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.
The following format directives print single components of the time.
H
I
k
l
p
Z
M
S
@
The following format directives print single components of the date.
a
A
b
h
B
m
d
w
j
U
W
Y
y
The following format directives print combinations of time and date components.
r
T
X
c
D
x
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.
Here is how to run a command on one file at a time.
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 ';'
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 $HOME -name '*.c' -print | grep -l sprintf
However, if the command needs to have its standard input be a terminal
(less, for example), you have to use the shell command
substitution method.
Because file names can contain quotes, backslashes, blank characters,
and even newlines, it is not safe to process them using xargs in its
default mode of operation. But since most files' names do not contain
blanks, this problem occurs only infrequently. If you are only
searching through files that you know have safe names, then you need not
be concerned about it.
In many applications, if xargs botches processing a file because
its name contains special characters, some data might be lost. The
importance of this problem depends on the importance of the data and
whether anyone notices the loss soon enough to correct it. However,
here is an extreme example of the problems that using blank-delimited
names can cause. If the following command is run daily from
cron, then any user can remove any file on the system:
find / -name '#*' -atime +7 -print | xargs rm
For example, you could do something like this:
eg$ 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
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.
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
--max-lines[=max-lines]
-l[max-lines]
--max-args=max-args
-n max-args
xargs will exit.
--max-chars=max-chars
-s max-chars
--max-procs=max-procs
-P max-procs
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.
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]
find bills -type f | xargs -iXX sort -o XX.sorted XXThe equivalent command using `find -exec' is:
find bills -type f -exec sort -o '{}.sorted' '{}' ';'
To ask the user whether to execute a command on a single file, you can
use the find primary `-ok' instead of `-exec':
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
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 \
\( -exec unstripped '{}' \; -fprint ubins -o -fprint sbins \)
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.
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.
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"
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.
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 \;
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.
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).
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.
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...'
--netpaths='path...'
--prunepaths='path...'
--output=dbfile
--netuser=user
su.
Default is daemon.
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.
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.
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)
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.
Each file has a set of permissions that control the kinds of access that users have to that file. The permissions for a file are also called its access mode. They can be represented either in symbolic form or as an octal number.
There are three kinds of permissions that a user can have for a file:
There are three categories of users who may have different permissions to perform any of the above operations on a file:
Files are given an owner and group when they are created. Usually the
owner is the current user and the group is the group of the directory
the file is in, but this varies with the operating system, the
filesystem the file is created on, and the way the file is created. You
can change the owner and group of a file by using the chown and
chgrp commands.
In addition to the three sets of three permissions listed above, a file's permissions have three special components, which affect only executable files (programs) and, on some systems, directories:
Symbolic modes represent changes to files' permissions as
operations on single-character symbols. They allow you to modify either
all or selected parts of files' permissions, optionally based on
their previous values, and perhaps on the current umask as well
(see section The Umask and Protection).
The format of symbolic modes is:
[ugoa...][[+-=][rwxXstugo...]...][,...]
The following sections describe the operators and other details of symbolic modes.
The basic symbolic operations on a file's permissions are adding, removing, and setting the permission that certain users have to read, write, and execute the file. These operations have the following format:
users operation permissions
The spaces between the three parts above are shown for readability only; symbolic modes can not contain spaces.
The users part tells which users' access to the file is changed. It consists of one or more of the following letters (or it can be empty; see section The Umask and Protection, for a description of what happens then). When more than one of these letters is given, the order that they are in does not matter.
u
g
o
a
The operation part tells how to change the affected users' access to the file, and is one of the following symbols:
+
-
=
The permissions part tells what kind of access to the file should be changed; it is zero or more of the following letters. As with the users part, the order does not matter when more than one letter is given. Omitting the permissions part is useful only with the `=' operation, where it gives the specified users no access at all to the file.
r
w
x
For example, to give everyone permission to read and write a file, but not to execute it, use:
a=rw
To remove write permission for from all users other than the file's owner, use:
go-w
The above command does not affect the access that the owner of the file has to it, nor does it affect whether other users can read or execute the file.
To give everyone except a file's owner no permission to do anything with that file, use the mode below. Other users could still remove the file, if they have write permission on the directory it is in.
go=
Another way to specify the same thing is:
og-rxw
You can base part of a file's permissions on part of its existing permissions. To do this, instead of using `r', `w', or `x' after the operator, you use the letter `u', `g', or `o'. For example, the mode
o+g
adds the permissions for users who are in a file's group to the permissions that other users have for the file. Thus, if the file started out as mode 664 (`rw-rw-r--'), the above mode would change it to mode 666 (`rw-rw-rw-'). If the file had started out as mode 741 (`rwxr----x'), the above mode would change it to mode 745 (`rwxr--r-x'). The `-' and `=' operations work analogously.
In addition to changing a file's read, write, and execute permissions, you can change its special permissions. See section Structure of File Permissions, for a summary of these permissions.
To change a file's permission to set the user ID on execution, use `u' in the users part of the symbolic mode and `s' in the permissions part.
To change a file's permission to set the group ID on execution, use `g' in the users part of the symbolic mode and `s' in the permissions part.
To change a file's permission to stay permanently on the swap device, use `o' in the users part of the symbolic mode and `t' in the permissions part.
For example, to add set user ID permission to a program, you can use the mode:
u+s
To remove both set user ID and set group ID permission from it, you can use the mode:
ug-s
To cause a program to be saved on the swap device, you can use the mode:
o+t
Remember that the special permissions only affect files that are executable, plus, on some systems, directories (on which they have different meanings; see section Structure of File Permissions). Using `a' in the users part of a symbolic mode does not cause the special permissions to be affected; thus,
a+s
has no effect. You must use `u', `g', and `o' explicitly to affect the special permissions. Also, the combinations `u+t', `g+t', and `o+s' have no effect.
The `=' operator is not very useful with special permissions; for example, the mode:
o=t
does cause the file to be saved on the swap device, but it also removes all read, write, and execute permissions that users not in the file's group might have had for it.
There is one more special type of symbolic permission: if you use `X' instead of `x', execute permission is affected only if the file already had execute permission or is a directory. It affects directories' execute permission even if they did not initially have any execute permissions set.
For example, this mode:
a+X
gives all users permission to execute files (or search directories) if anyone could before.
The format of symbolic modes is actually more complex than described above (see section Setting Permissions). It provides two ways to make multiple changes to files' permissions.
The first way is to specify multiple operation and permissions parts after a users part in the symbolic mode.
For example, the mode:
og+rX-w
gives users other than the owner of the file read permission and, if it is a directory or if someone already had execute permission to it, gives them execute permission; and it also denies them write permission to it file. It does not affect the permission that the owner of the file has for it. The above mode is equivalent to the two modes:
og+rX og-w
The second way to make multiple changes is to specify more than one simple symbolic mode, separated by commas. For example, the mode:
a+r,go-w
gives everyone permission to read the file and removes write permission on it for all users except its owner. Another example:
u=rwx,g=rx,o=
sets all of the non-special permissions for the file explicitly. (It gives users who are not in the file's group no permission at all for it.)
The two methods can be combined. The mode:
a+r,g+x-w
gives all users permission to read the file, and gives users who are in the file's group permission to execute it, as well, but not permission to write to it. The above mode could be written in several different ways; another is:
u+r,g+rx,o+r,g-w
If the users part of a symbolic mode is omitted, it defaults to
`a' (affect all users), except that any permissions that are
set in the system variable umask are not affected.
The value of umask can be set using the
umask command. Its default value varies from system to system.
Omitting the users part of a symbolic mode is generally not useful
with operations other than `+'. It is useful with `+' because
it allows you to use umask as an easily customizable protection
against giving away more permission to files than you intended to.
As an example, if umask has the value 2, which removes write
permission for users who are not in the file's group, then the mode:
+w
adds permission to write to the file to its owner and to other users who are in the file's group, but not to other users. In contrast, the mode:
a+w
ignores umask, and does give write permission for
the file to all users.
File permissions are stored internally as 16 bit integers. As an alternative to giving a symbolic mode, you can give an octal (base 8) number that corresponds to the internal representation of the new mode. This number is always interpreted in octal; you do not have to add a leading 0, as you do in C. Mode 0055 is the same as mode 55.
A numeric mode is usually shorter than the corresponding symbolic mode, but it is limited in that it can not take into account a file's previous permissions; it can only set them absolutely.
The permissions granted to the user, to other users in the file's group, and to other users not in the file's group are each stored as three bits, which are represented as one octal digit. The three special permissions are also each stored as one bit, and they are as a group represented as another octal digit. Here is how the bits are arranged in the 16 bit integer, starting with the lowest valued bit:
Value in Corresponding
Mode Permission
Other users not in the file's group:
1 Execute
2 Write
4 Read
Other users in the file's group:
10 Execute
20 Write
40 Read
The file's owner:
100 Execute
200 Write
400 Read
Special permissions:
1000 Save text image on swap device
2000 Set group ID on execution
4000 Set user ID on execution
For example, numeric mode 4755 corresponds to symbolic mode `u=rwxs,go=rx', and numeric mode 664 corresponds to symbolic mode `ug=rw,o=r'. Numeric mode 0 corresponds to symbolic mode `ugo='.
Below are summaries of the command line syntax for the programs discussed in this manual.
findfind [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
--version
find and exit.
locatelocate [option...] pattern...
--database=path
-d path
LOCATE_PATH to set the list of database files to search. The
option overrides the environment variable if both are used.
--help
locate and exit.
--version
locate and exit.
updatedbupdatedb [option...]
--localpaths='path...'
--netpaths='path...'
--prunepaths='path...'
--output=dbfile
--netuser=user
su(1).
Default is daemon.
xargsxargs [option...] [command [initial-arguments]]
xargs exits with the following status:
--null
-0
--eof[=eof-str]
-e[eof-str]
--help
xargs and exit.
--replace[=replace-str]
-i[replace-str]
--max-lines[=max-lines]
-l[max-lines]
--max-args=max-args
-n max-args
xargs will exit.
--interactive
-p
--no-run-if-empty
-r
--max-chars=max-chars
-s max-chars
--verbose
-t
--version
xargs and exit.
--exit
-x
--max-procs=max-procs
-P max-procs
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.
Jump to: -
This document was generated on 7 November 1998 using the texi2html translator version 1.52.