Linux Selection Information Command Introduction and application 20170331

Before you introduce the command to select information, say the pipe symbol "|" With the TR command, because it is often used when multiple commands are used together.

One, using the pipe symbol provided by Linux "|" Separates the two commands, and the output from the left command of the pipe character is entered as the command to the right of the pipe. Continuous use

The pipeline means that the output of the first command will be entered as the second command, and the output of the second command will be entered as the third command, and so on. Let's see how the pipeline is applied in constructing a Linux command.

1. Use a pipeline

# Rpm-qa|grep Licq

This command uses a pipe symbol "|" Set up a pipeline. The pipeline lists the output of the RPM-QA command (including all installed RPM packages in the system) as input to the grep command, listing the RPM packets with LICQ characters.

2. Using multiple pipelines

# CAT/ETC/PASSWD | Grep/bin/bash | Wc-l

This command uses two pipelines, using the first pipe to send the output of the cat command (which displays the contents of the passwd file) to the grep command, and the grep command to find all rows containing "/bin/bash", and the second pipe to send the output of grep to the WC command. The WC command counts the number of rows in the input. The function of this command is to find out how many users in the system are using bash.

such as: $. Cat </ETC/MOTD |./a.out

< indicates the meaning of the input redirection, which is to replace the file with the < followed by the keyboard as the new input device.

| The meaning of a pipe can be understood as something flowing from one side of the pipe to the other side.

Your command means reading from the/ETC/MOTD file and then executing the a.out command with the contents read by the Cat command as an input parameter to the following command a.out.

3. Use the pipeline to filter the results using grep and enter the rows containing the specified information

Command | grep < matching information >

bash-4.1$ Cat Error-2015-12-22.log | grep ERROR

10:05:31.824 [http-/192.168.0.80:8080-10] ERROR c.e.p.f.fastdfs.fastdfsclientimpl[97]-recv Package

Size-1! = 10

15:54:26.458 [http-/192.168.0.80:8080-6] ERROR c.e.p.f.fastdfs.fastdfsclientimpl[97]-recv Package

Size-1! = 10<span style= "FONT-SIZE:18PX;" ><strong><span style= "color: #ff0000;" >

</span></strong></span>

The TR command can replace, compress, and delete characters from the standard input. It can turn a set of characters into another set of characters, often used to write graceful single-line commands, powerful.

Syntax TR (option)

(parameter) option-C or--complerment: Replaces all characters that are not part of the first character set;

-D or--delete: Deletes all characters belonging to the first character set;

-S or--squeeze-repeats: the consecutive repeating character is represented by a single character;

-T or--truncate-set1: First remove the characters from the first character set that are more than the second character set.

Parameters

Character Set 1: Specifies the original character set to be converted or deleted. When performing a conversion operation, the target character set of the transformation must be specified using the parameter "character Set 2". However, when performing a delete operation, the parameter "character Set 2" is not required;

Character Set 2: Specifies the target character set to convert to.

Third, grep

Command format

grep [OPTIONS] PATTERN [FILE ...]

1. Find out if the specified information exists in the file:

grep < Find information > < file name >

2. Find in multiple files:

grep < Find information > < file name > < filename > ....

3. Use-l to find the file name containing the specified information

Grep-l < Find information > < file name > < filename > ....

-I,--ignore-case ignore case

-X,--line-regexp full line match

Synonyms for-y "-I."

-W,--word-regexp word match

-V,--invert-match shows rows that are not matched by the pattern, matching rows are not displayed

General output Control:

-C,--count gets the number of matching rows. Example:

[Email protected] ~]$ grep-c-V "nologin"/etc/passwd

--color[=when],--colour[=when] match, highlight "default red font".

Example: [[email protected] ~]$ grep--color "Nologin"/etc/passwd

grep usage: http://blog.csdn.net/wangxin1982314/article/details/50464259

http://blog.csdn.net/woshizhangliang999/article/details/46859161

Iv. Find

Find Files

Find./-type F

Find a Directory

Find./-type D

Find a file or directory with the name test

Find./-name Test

Look for a file whose name matches the regular expression, and note the preceding '. * ' (found file with directory)

Find./-regex. *so.*\.gz

Find the directory and list the files under the directory (the LS command is executed separately for each directory found, no option-print the directory name is not displayed on the previous line of the file list)

Find./-type d-print-exec ls {} \;

Locate the directory and list the files in the directory (the LS command is executed separately for each directory found, and you need to confirm before executing the command)

Find./-type d-ok ls {} \;

Find the directory and list the files under the directory (add the found directory to the LS command one time after execution, the parameters will be executed multiple times when the parameter is too long)

Find./-type d-exec ls {} +

Find files with file names matching *.c

Find./-name \*.c

Prints the contents of the test file after printing the test filename

Find./-name test-print-exec cat {} \;

Do not print the test file name, only the contents of test files

Find./-name test-exec cat {} \;

Find files that are less than two days away from the current time of file update date

Find./-mtime-2

Files that are more than two days away from the current time when you find file update days

Find./-mtime +2

Find files that are less than two days away from the current time of day when files are updated

Find./-mtime 2

Find files that are less than two minutes from the current time when the file is updated

Find./-mmin-2

Find files that are more than two minutes from the current time when the file is updated

Find./-mmin +2

Find files that are less than two minutes away from the current time when a file is updated

Find./-mmin 2

Find file update time than file ABC content update time new file

Find./-newer ABC

Find file access times than file ABC content update time new files

Find./-anewer ABC

Find empty files or empty directories

Find./-empty

Find empty files and delete

Find./-empty-type F-print-delete

Find a file or directory with permission 644 (requires full compliance)

Find./-perm 664

Find files or directories where user/group permissions are read-write, other user rights are readable (other permissions are not limited)

Find./-perm-664

Find files or directories where the user has write permission or the group user has write permission

Find./-perm/220

Find./-perm/u+w,g+w

Find./-perm/u=w,g=w

Find directories or files with Read permission for owner permissions

Find./-perm-u=r

Find directories or files with Read permission for user group permissions

Find./-perm-g=r

Find directories or files with Read permission for other user rights

Find./-perm-o=r

Five, cut

Cut is a selection command that analyzes a piece of data and takes out what we want. In general, the selection of information is usually for "line" to analyze, not the entire information analysis.

(1) The syntax format is:

Cut [-bn] [file] or cut [-c] [file] or cut [-DF] [file]

Instructions for use

The cut command cuts bytes, characters, and fields from each line of the file and writes those bytes, characters, and fields to standard output.

If you do not specify a File parameter, the Cut command reads standard input. One of the-B,-C, or-f flags must be specified.

Main parameters

-B: Split in bytes. These byte locations will ignore multibyte character boundaries unless the-n flag is also specified.

-C: Split in characters.

-D: Custom delimiter, default is tab.

-F: Used with-D to specify which area to display.

-N: Cancels splitting multibyte characters. Used only with the-B flag. If the last byte of the character falls within the range of <br/> indicated by the List parameter of the-B flag, the character will be written out; otherwise, the character will be excluded.

(2) What is cut generally based on? In other words, how do I tell cut what I want to locate?

The cut command mainly accepts three positioning methods:

First, byte (bytes), with option-B

Second, character (characters), with option-C

Third, domain (fields), with option-f

(3) Positioning as "byte"

For example, when you execute the PS command, it will output something like this:

[email protected] programming]$ who

rocrocket:0 2009-01-08 11:07

Rocrocket pts/0 2009-01-08 11:23 (: 0.0)

Rocrocket pts/1 2009-01-08 14:15 (: 0.0)

If we want to extract the 3rd byte of each row, that's it:

[Email protected] programming]$ Who|cut-b 3

C

C

C

(4) If "byte" is located, I want to extract the 3rd, 4th, 5th and 8th bytes, what should I do?

-B supports the notation of form 3-5, and multiple positions are separated by commas. Let's take a look at examples:

[Email protected] programming]$ Who|cut-b 3-5,8

Croe

Croe

Croe

But one thing to note is that if the-B option is used for the cut command, the cut will sort all the positions after-B, from small to large, when the command is executed.

And then extract. Can not reverse the order of positioning Oh. This example can illustrate the problem:

[Email protected] programming]$ Who|cut-b 8,3-5

Croe

Croe

Croe

(5) What are the "3-5" tips, please?

[email protected] programming]$ who

rocrocket:0 2009-01-08 11:07

Rocrocket pts/0 2009-01-08 11:23 (: 0.0)

Rocrocket pts/1 2009-01-08 14:15 (: 0.0)

[Email protected] programming]$ Who|cut-b-3

Roc

Roc

Roc

[Email protected] programming]$ Who|cut-b 3-

crocket:0 2009-01-08 11:07

Crocket pts/0 2009-01-08 11:23 (: 0.0)

Crocket pts/1 2009-01-08 14:15 (: 0.0)

As you can see, 3 means from the first byte to the third byte, and 3-from the third byte to the end of a line. If you are careful, you can see that in both cases, the third byte "C" is included.

What do you think would happen if I executed Who|cut-b -3,3-? The answer is to output an entire line, without the occurrence of two consecutive overlapping c. See:

[Email protected] programming]$ Who|cut-b -3,3-

rocrocket:0 2009-01-08 11:07

Rocrocket pts/0 2009-01-08 11:23 (: 0.0)

Rocrocket pts/1 2009-01-08 14:15 (: 0.0)

(6) Give the simplest example of a character-based marker!

The following example you déjà vu, extract the 3rd, 4th, 5th and 8th characters:

[Email protected] programming]$ who|cut-c 3-5,8

Croe

Croe

Croe

But, what's the difference between looking and B? Does B and C function the same? In fact, it looks the same, just because this example is not good, who output is a single-byte character, so with-B and c no difference, if you extract Chinese, the difference is seen, to see the situation of Chinese extraction:

[email protected] programming]$ cat Cut_ch.txt

Monday

Tuesday

Wednesday

Thursday

[Email protected] programming]$ Cut-b 3 cut_ch.txt

?

?

?

?

[Email protected] programming]$ cut-c 3 cut_ch.txt

One

Two

Three

Four

See, with-C will be in character units, the output is normal, and-B will only be silly in bytes (8-bit bits) to calculate, the output is garbled.

Now that we have mentioned this point of knowledge, I would like to add that if you learn more, you can improve it.

When you encounter multibyte characters, you can use the-n option, which is used to tell the cut not to disassemble multibyte characters. Examples are as follows:

[email protected] programming]$ cat Cut_ch.txt |cut-b 2

?

?

?

?

[email protected] programming]$ cat Cut_ch.txt |CUT-NB 2

[email protected] programming]$ cat Cut_ch.txt |CUT-NB

Star

Star

Star

Star

(7) What's going on in the field? Explanation and explanation:)

Why is there a "domain" extraction, because the B and C just mentioned can only extract information in a fixed-format document, and for non-fixed-format information is helpless. This is where "domain" comes in handy. If you look at the/etc/passwd file, you will find that it is not the same format as the WHO output, but rather fragmented emissions. However, the colon plays a very important role in each line of the file, and the colon is used to separate each item.

We are fortunate that the cut command provides such an extraction method, specifically to set the "spacer", and then set the "Extract the first few domains", OK!

Take the first five elements of/etc/passwd as an example:

[Email protected] programming]$ Cat/etc/passwd|head-n 5

Root:x:0:0:root:/root:/bin/bash

Bin:x:1:1:bin:/bin:/sbin/nologin

Daemon:x:2:2:daemon:/sbin:/sbin/nologin

Adm:x:3:4:adm:/var/adm:/sbin/nologin

Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

[[email protected] programming]$ cat/etc/passwd|head-n 5|cut-d:-F 1

Root

Bin

Daemon

Adm

Lp

See, use-D to set the delimiter is a colon, and then use-F to set the first domain I want to take, and then press ENTER, all the user names are listed! Oh, there is a sense of accomplishment!

Of course, when you set-F, you can also use a format such as 3-5 or 4-similar:

[Email protected] programming]$ cat/etc/passwd|head-n 5|cut-d:-F 1,3-5

Root:0:0:root

Bin:1:1:bin

Daemon:2:2:daemon

Adm:3:4:adm

Lp:4:7:lp

[Email protected] programming]$ cat/etc/passwd|head-n 5|cut-d:-F 1,3-5,7

Root:0:0:root:/bin/bash

Bin:1:1:bin:/sbin/nologin

Daemon:2:2:daemon:/sbin/nologin

Adm:3:4:adm:/sbin/nologin

Lp:4:7:lp:/sbin/nologin

[Email protected] programming]$ cat/etc/passwd|head-n 5|cut-d:-f-2

Root:x

Bin:x

Daemon:x

Adm:x

Lp:x

(8) If you encounter spaces and tabs, how to distinguish it? I feel a little bit messy, how to do?

Sometimes the tab is really difficult to identify, there is a way to see whether a space is composed of a number of spaces or a tab character.

[email protected] programming]$ cat Tab_space.txt

This is tab finish.

This is several space finish.

[Email protected] programming]$ sed-n l tab_space.txt

This is tab\tfinish.$

This is several space finish.$

See, if it is a tab (tab), then it will be displayed as the \ t symbol, if it is a space, it will be displayed as is.

Tabs and spaces can be judged by this method.

Note that the character behind the sed-n is the lowercase letter of L. Oh, don't look wrong.

(9) What symbols should I use in cut-d to set tabs or spaces?

In fact, the default spacer of the-D option for cut is a tab, so when you are going to use a tab, you can omit the-D option and use-F to take the domain directly.

If you set a space as a spacer, that's it:

[email protected] programming]$ cat tab_space.txt |cut-d '-F 1

This

This

Note that there is a space between the two single quotes that you really want to have. Oh, don't be lazy.

Also, you can only set a space after-D, you don't have to set multiple spaces, because cut only allows the spacer to be one character.

[email protected] programming]$ cat tab_space.txt |cut-d '-F 1

Cut:the delimiter must is a single character

Try ' Cut--help ' for more information.

(ten) What are the defects and deficiencies of the cut?

Did you guess? Yes, when dealing with multiple spaces.

If some of the fields in the file are spaced by several spaces, then using cut is a bit of a hassle, because cut is only good at working with "one character interval" text content

Examples of selecting information commands:

Run the route command to get the routing information and then crawl the information that contains the default row

Then remove the extra space and compress it into a space.

Finally, the second area, the IP address, is displayed as a space separator.

if (RUNSYSCMD2 ("route | grep Default | Tr-s ' | Cut-d '-f2 ',

Gateway, sizeof (gateway)) = = ld_success)

Linux Selection Information Command Introduction and application 20170331