Basic parsing of Linux operating system (iv)--linux essential Command Anatomy (2)

11.cat: External command

Features: Connect files and display connection results in standard output

Format: Cat [OPTION] ... [FILE] ...

Common options:

-A,--show-all: equivalent to-vet

-B,--number-nonblank: The contents of the output are numbered by row, but blank lines are not numbered

-e: Equivalent to-ve

-E,--show-ends: Displays the "$" character at the end of each line

-N,--number: A row number that is not differentiated by the contents of all outputs

-S,--squeeze-blank: Merge multiple lines of contiguous whitespace lines in a row

-T: equivalent to-VT

-T,--show-tabs: Displays tabs as "^i" characters

-V,--show-nonprinting: replace non-printable characters with "^" and "M" in addition to newline and tab stops

Exit Status:

If the command executes successfully, the status return value is 0, or if the command execution fails, the status return value is not 0.

Examples of Use:

[email protected] test]# Cat Windows.txt This is a file in Windows. From Windowsto linux OK [[e-mail protected] test]# cat-a windows.txt This was A file in windows.^m$ from Windo Ws^ito linux^m$ ok^m$

12.head: External command

Function: Displays the beginning of the file, the first 10 lines are displayed by default

Format: Head [OPTION] ... [FILE] ...

Common options:

-C,--bytes=[-]k: Displays the number of bytes of the first k in each file, and if "-" is used, it displays everything except the last K number of bytes in the file.

-N,--lines=[-]k: Displays the number of rows for the first k number of each file, rather than the first 10 lines of the file, and if you use "-", all the contents of the file except for the last number of k lines.

-Q,--quiet,--silent: Never display the file name as a header format

-V,--verbose: Always display the file name as a header format

K can have multiple suffixes: b, KB, K, MB 1000*1000, M 1024*1024, GB 1000*1000*1000, G 1024*1024*1024, for subsequent units T, P, E, Z, Y and so on. Use.

Exit Status:

If the command executes successfully, the status return value is 0, or if the command execution fails, the status return value is not 0.

Examples of Use:

[email protected] test]# cat file1 testend This is a test file hehe [[email protected] test]# Head-n 1 File1 testend [[email protected] test]# head-n-1 file1 testend This is a test file [[email protected] t est]#

13.tail: External command

Function: Outputs the section at the end of the specified file

Format: tail [OPTION] ... [FILE] ...

Common options:

-C,--bytes=k: The last K bytes of the output file, if +k is used, starts from the first K bytes of the file

-F,--follow[={name|descriptor}]: Tracks changes to the specified file, does not exit after output, and continues to monitor file changes

-F: Equivalent to the combination of--follow=name and--retry

-N,--lines=k: The last K line of the output file, if +k is used, starts from the file's K-line

-S,--sleep-interval=n: With the-f option, delay N seconds during two repeat checks.

Exit Status:

If the command executes successfully, the status return value is 0, or if the command execution fails, the status return value is not 0.

Examples of Use:

[[email protected] test]# cat windows.txt I AM in Windows now-a file of Windows there is a Tabhere OK end [[email protected] test]# Tail-n 2 windows.txt There is a tabhere ok end [[email protected] test]# Tail-n +2 windows.txt A file of Windows there is a tabhere ok end [[email protected] test]#

14.more: External command

Function: Using the monitor to display the file's intensive filtering program

Format: More [options] file [...]

Common options:

-num: Number of rows displayed at one time

-D: Display below the screen [press space to continue, ' Q ' to quit.] To prompt the user, if the user presses the wrong key, the [press ' H ' for instructions.] Instead of the ' beep ' sound

-L: Cancel the feature that pauses when meeting special characters ^l (paper feed)

-P: Do not scroll to display each page, but first clear the screen and then display the content

C: Similar to-P, the difference is to display the content before clearing other old information

-S: A blank line that is substituted for a row when it encounters a blank line that has more than two consecutive lines

+/pattern: Searches for the string (pattern) before each file is displayed, and then starts displaying after the string

+num: starting from Num line

More than some vi-based interactive commands

H,?: View Help Tips

Space, Z, F, ^f, S: page by screen

B, ^b: Page UP, but only when viewing the file, using the pipeline is not valid

Q, Q: Exit

V: Call VI Editor for file editing operations

: F: Displays the current file name and the current line number

.: Repeat the previous command

Exit Status:

A non-0 status value is returned only if the specified error is selected, and the other condition returns a value of 0.

15.less: External command

Features: pagination displays text document content, relative to more

Format: less [option] ... [FileName] ...

Common options:

-e: After the file content is displayed, automatic exit;

-F: Force the display of special files, such as devices, directories, or binaries;

-G: Do not highlight all search keywords, display only the currently displayed keywords, to improve the display speed;

-I: ignoring case when searching

-M: show percentages similar to more commands

-N: Line number is displayed at the beginning of each line;

-O < filename: Save less output in the specified file

-Q: Do not use warning tones

-S: Compress successive empty lines into one line;

-S: Displays longer content in a single line, without wrapping the display;

-x<: Displays the tab character as a specified number of space characters.

Less also has its own interactive commands, which are generally similar to more, but not exactly the same.

/string: Search down the function of "string"

String: The ability to search up "string"

N: Repeat the previous search (with/or?). About

N: Reverse repeats the previous search (and/or?) About

B: Turn back one page

D: Turn back half a page

H: Display Help interface

Q: Exit less command

U: Scroll forward half page

Y: Scrolls forward one line

SPACEBAR: Scrolls one line

Enter: Scroll one page

[PgDn]: Flip one PAGE Down

[PgUp]: Flip one page Up

Exit Status:

A non-0 status value is returned only if the parameter file does not exist, and the other condition returns a value of 0

16.date: External command

Function: Display and set the system date and time

Format:

Date [OPTION] ... [+format]

Date [-u|--utc|--universal] [MMDDHHMM[[CC]YY][.SS]]

Common options:

-D,--date=string: Displays the time description by ' STRING ' instead of the current time

-S,--set=string: Set the system time by ' STRING '

In addition to the options, the date command can support powerful format sequences:

If you need to display the date in the specified format, you can use the "+" character to connect any one of the following formats, and each "+" character can have only one format

%a: Abbreviated format of the week (SUN-SAT)

%A: Full name format of the week (Sunday-saturday)

%b: abbreviated format of the month (JAN-DEC)

%B: Full name format for month (January-december)

%c: Display date and time directly

%d: Day of January (01-31)

%d: show date directly (MM/DD/YY)

%F: Full date, equivalent to%y-%m-%d

%h: With%b

%H: Hours (00-23)

%I: Hours (01-12)

%j: The first day of the Year (001-366)

%k: Hours (0-23)

%l: Hours (1-12)

%m: Month (01-12)

%M: minutes (00-59)

%n: Next line

%p: Show local AM or PM

%r: Direct Display time (12-hour format, HH:MM:SS [ap]m)

%s: The number of seconds since January 1, 1970 00:00:00 to date

%s: Seconds (00-60)

%t: Jump grid

%T: Full time, equivalent to%h:%m:%s

%u: Week of the Year (00-53) (Sunday is the first day of the week)

%w: Day of the Week (0-6)

%W: Week of the Year (00-53) (with Monday as the first day of the week)

%x: equivalent (%h:%m:%s am| PM)

%x: Full Date (%m/%d/%y)

%y: Abbreviated year (00-99)

%Y: Full year (0000-9999)

%Z: Show time zone

These formats do not have to be remembered, only a few common ones. such as%f,%T,%Y,%m,%d,%H,%m,%s

Exit Status:

If the command executes successfully, the status return value is 0, or if the command execution fails, the status return value is not 0.

Examples of Use:

[[Email protected] test]# date Sun may 15:11:09 CST [[email protected] test]# date +%f 2016-05-22 [Email protected] test]# date +%t 15:11:49 [[email protected] test]# date +%a-d ' 2 days ago ' Friday [email Protected] test]# date +%a Sunday [[email protected] test]#

17.hwclock: External command

Function: query or set hardware clock (RTC)

Format: hwclock [function] [option ...]

Common options:

--set: Sets the hardware clock based on the time given by the--date option

-S,--hctosys: Adjusts the system time according to the hardware clock

-W,--SYSTOHC: Adjusts the hardware clock according to the system time

--SYSTZ: Set the kernel time zone and reset the system time based on the current time zone

Examples of Use:

[Email protected] ~]# hwclock--set--date= "2016/05/22 15:32:36" [[email protected] ~]# hwclock-s [[Email Prot Ected] ~]# date Sun may 15:32:44 CST 2016

18.tree: External command

Function: Display the contents of a directory using a tree-like structure list

Format: Tree [option] ... [Directory ...]

Common options:

-A: Shows those with "." or ".." The hidden file that starts with the default tree cannot be displayed when the

-D: Show only directory names

-L: Do not allow recursive querying of directory Symbolic links

-F: Each file is to be displayed with an absolute path

-X: Just stay on the current file system

-L Level: Indicates the maximum display depth for the directory tree

Examples of Use:

[Email protected] test]# pwd/test [[email protected] test]# Tree/test/test├──num.txt├──testdir    │├──dir1│└──dir2└──windows.txt 3 Directories, 2 files [[email protected] test]# tree-d/test /TEST└──TESTDIR├──DIR1└──DIR2 3 directories [[email protected] test]#

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Basic parsing of Linux operating system (iv)--linux essential Command Anatomy (2)