find command in Linux

find

find [pathnames] [conditions]

An extremely useful command for finding particular groups of files (numerous examples follow this description). find descends the directory tree beginning at each pathname and locates files that meet the specified conditions. The default pathname is the current directory. The most useful conditions include -name and -type (for general use), -exec and -size (for advanced use), and -mtime and -user (for administrators).

Conditions may be grouped by enclosing them in \( \) (escaped parentheses), negated with !, given as alternatives by separating them with -o, or repeated (adding restrictions to the match; usually only for -name, -type, or -perm). Note that "modification" refers to editing of a file's contents, whereas "change" means a modification, or permission or ownership changes. In other words, -ctime is more inclusive than -atime or -mtime.

Conditions and actions

-amin +n| -n| n

Find files last accessed more than n (+n), less than n (-n), or exactly n minutes ago.

-anewer file

Find files that were accessed after file was last modified. Affected by -follow when after -follow on the command line.

-atime +n| -n| n

Find files that were last accessed more than n (+n), less than n (-n), or exactly n days ago. Note that find changes the access time of directories supplied as pathnames.

-cmin +n| -n| n

Find files last changed more than n (+n), less than n (-n), or exactly n minutes ago.

-cnewer file

Find files that were changed after they were last modified. Affected by -follow when after -follow on the command line.

-ctime +n| -n| n

Find files that were changed more than n (+n), less than n (-n), or exactly n days ago. A change is anything that changes the directory entry for the file, such as a chmod.

-daystart

Calculate times from the start of the day today, not 24 hours ago.

-depth

Descend the directory tree, skipping directories and working on actual files first, and then the parent directories. Useful when files reside in unwritable directories (e.g., when using find with cpio).

-empty

Continue if file is empty. Applies to regular files and directories.

-exec command{ } \ ;

Run the Linux command, from the starting directory on each file matched by find (provided command executes successfully on that file—i.e., returns a 0 exit status). When command runs, the argument { } substitutes the current file. Follow the entire sequence with an escaped semicolon (\;). In some shells, the braces may need to be escaped as well.

-false

Return false value for each file encountered.

-follow

Follow symbolic links and track the directories visited (don't use with -type l).

-fstype type

Match files only on type filesystems. Acceptable types include minix, ext, ext2, xia, msdos, umsdos, vfat, proc, nfs, iso9660, hpfs, sysv, smb, and ncpfs.

-gid num

Find files with numeric group ID of num.

-group gname

Find files belonging to group gname. gname can be a group name or a group ID number.

-ilname pattern

A case-insensitive version of -lname.

-iname pattern

A case-insensitive version of -name.

-inum n

Find files whose inode number is n.

-ipath pattern

A case-insensitive version of -path.

-iregex pattern

A case-insensitive version of -regex.

-links n

Find files having n links.

-lname pattern

Search for files that are symbolic links, pointing to files named pattern. pattern can include shell metacharacters and does not treat / or . specially. The match is case-insensitive.

-maxdepth num

Do not descend more than num levels of directories.

-mindepth num

Begin applying tests and actions only at levels deeper than num levels.

-mmin +n| -n| n

Find files last modified more than n (+n), less than n (-n), or exactly n minutes ago.

-mount, -xdev

Search only for files that reside on the same filesystem as pathname.

-mtime +n| -n| n

Find files that were last modified more than n (+n), less than n (-n), or exactly n days ago. A modification is a change to a file's data.

-name pattern

Find files whose names match pattern. Filename metacharacters may be used but should be escaped or quoted.

-newer file

Find files that were modified more recently than file; similar to -mtime. Affected by -follow only if it occurs after -follow on the command line.

-nogroup

The file's group ID does not correspond to any group.

-noleaf

Normally, find assumes that each directory has at least two hard links that should be ignored (a hard link for its name and one for "."--i.e., two fewer "real" directories than its hard link count indicates). -noleaf turns off this assumption, a useful practice when find runs on non-Unix-style filesystems. This forces find to examine all entries, assuming that some might prove to be directories into which it must descend (a time-waster on Unix).

-nouser

The file's user ID does not correspond to any user.

-ok command { }\;

Same as -exec, but prompts user to respond with y before command is executed.

-path pattern

Find files whose names match pattern. Expect full pathnames relative to the starting pathname (i.e., do not treat / or . specially).

-perm nnn

Find files whose permission flags (e.g., rwx) match octal number nnn exactly (e.g., 664 matches -rw-rw-r--). Use a minus sign before nnn to make a "wildcard" match of any unspecified octal digit (e.g., -perm -600 matches -rw-******, where * can be any mode).

-print

Print the matching files and directories, using their full pathnames. Return true. This is the default behavior.

-regex pattern

Like -path, but uses grep-style regular expressions instead of the shell-like globbing used in -name and -path.

-size n[c]

Find files containing n blocks, or if c is specified, n characters long.

-type c

Find files whose type is c. c can be b (block special file), c (character special file), d (directory), p (fifo or named pipe), l (symbolic link), s (socket), or f (plain file).

-user user

Find files belonging to user (name or ID).

Examples

List all files (and subdirectories) in your home directory:

find $HOME -print

List all files named chapter1 in the /work directory:

find /work -name chapter1

List all files beginning with memo owned by ann:

find /work -name 'memo*' -user ann -print

Search the filesystem (begin at root) for manpage directories:

find / -type d -name 'man*' -print

Search the current directory, look for filenames that don't begin with a capital letter, and send them to the printer:

find . \! -name '[A-Z] *' -exec lpr { }\;

Find and compress files whose names don't end with .gz:

gzip `find . \! -name '*.gz' -print`

Remove all empty files on the system (prompting first):

find / -size 0 -ok rm { } \;

Search the system for files that were modified within the last two days (good candidates for backing up):

find / -mtime -2 -print

Recursively grep for a pattern down a directory tree:

find /book -print | xargs grep '[Nn] utshell'

If the files kt1 and kt2 exist in the current directory, their names can be printed with the command:

$ find . -name 'kt[0-9] ' ./kt1 ./kt2

Since the command prints these names with an initial ./ path, you need to specify the ./ when using the -path option:

$ find . -path './kt[0-9] ' ./kt1 ./kt2

The -regex option uses a complete pathname, like -path, but treats the following argument as a regular expression rather than a glob pattern (although in this case the result is the same):

$ find . -regex './kt[0-9] ' ./kt1 ./kt2

The Ultimate Rejection Letter

---

Herbert A. Millington
Chair - Search Committee
412A Clarkson Hall, Whitson University
College Hill, MA  34109

Dear Professor Millington,

Thank you for your letter of March 16.  After careful consideration, I
regret to inform you that I am unable to accept your refusal to offer me
an assistant professor position in your department.

This year I have been particularly fortunate in receiving an unusually
large number of rejection letters.  With such a varied and promising field
of candidates, it is impossible for me to accept all refusals.

Despite Whitson's outstanding qualifications and previous experience in
rejecting applicants, I find that your rejection does not meet my needs at
this time.  Therefore, I will assume the position of assistant professor
in your department this August.  I look forward to seeing you then.

Best of luck in rejecting future applicants.

Sincerely,
Chris L. Jensen

Xauthority Error in SSH connection.

xauth -b quit

This command will the xuthoirty locks after errors.

Reynolds number(雷诺数Re)

Reynolds number(雷诺数Re)

Reynolds number(雷诺数Re) 液体的流动状态可用雷诺数判断。 雷诺数定义为 式中，d—流束的特征长度，单位：m； V—流体的平均流速，单位m/s； ν—液体的运动粘度，单位：m2/s；或者，在CGS单位制中：cm2/s（斯）； μ—流体的动力粘度，也称绝对粘度，单位：Pa.s，它表示了单位速度梯度时内摩擦且应力的大小，μ之所以叫动力粘度，是因为在其量纲中存在动力学因素。 注： l 对于圆形截面管路，其特征长度一般取管路直径D； l 对于非圆形截面管路，雷诺数定义为 水力直径dH可用下式计算 式中，A—液流的有效面积；χ—液流的湿周（液流有效截面的周界长度）。 l 对外流问题，v、d一般取远前方来流速度和物体主要尺寸(如机翼弦长或圆球直径) 物理意义：流体力学中表示粘性影响的相似准数。Re是一个无因次量。 表示了流体流动时的惯性力Fg和粘性力(内摩擦力)Fm之比，它表示着流体流动的状态。 l 雷诺数Re小，意味着流体流动时各质点间的粘性力占主要地位，流体各质点平行于管路内壁有规则地流动，呈层流流动状态。 l 雷诺数Re大，意味着惯性力占主要地位，流体呈紊流流动状态， 一般管道雷诺数 Re＜2000为层流状态， Re＞4000为紊流状态， Re＝2000～4000为过渡状态。 在不同的流动状态下，流体的运动规律．流速的分布等都是不同的，因而管道内流体的平均流速υ与最大流速υmax的比值也是不同的。因此雷诺数的大小决定了粘性流体的流动特性。 外部条件几何相似时(几何相似的管子，流体流过几何相似的物体等)，若它们的雷诺数相等，则流体流动状态也是几何相似的(流体动力学相似)。这一相似规律正是流量测量节流装置标准化的基础。

tar command for bz2 files.

Use

In Unix, bzip2 can be used combined with or independently of tar: bzip2 file to compress and bzip2 -d file.bz2 to uncompress (the alias bunzip2 for decompression may also be used).

bzip2's command line flags are mostly the same as in gzip. So, to extract from a bzip2-compressed tar-file:

bzip2 -d <archivefile.tar.bz2 | tar -xvf -     or
bunzip2 <archivefile.tar.bz2 | tar -xvf -

To create a bzip2-compressed tar-file:

tar -cvf - filenames | bzip2 >archivefile.tar.bz2

GNU tar supports a -j flag, which allows creation of tar.bz2 files without a pipeline:

tar -cvjf archivefile.tar.bz2 file-list 

Decompressing in GNU tar:

tar -xvjf archivefile.tar.bz2