Linux Learning Diary--Basic Commands (4)--Text processing, redirection, pipelines

Open files have a Fd:file descriptor (file descriptor)

Standard input: Keyborad, 0
Standard output: monitor, 1
Standard error Output: monitor, 2

I/O redirection: Changing the standard location

output Redirect: command > New_pos, command >> new_pos
Overwrite redirect, the original content in the target file will be erased;
>>: Append redirect, the new content will append to the end of the target file;

# set-c: Suppresses the output of content to an existing file;
Forced Overwrite: >|
# Set +c:

2>: Overwrite redirect error output data stream;
2>>: Append redirect error output data stream;

The standard output and error outputs are directed to different locations:
COMMAND >/path/to/file.out 2>/path/to/error.out

Merge standard output and error output redirect for the same data stream:
&>: Overwrite redirect
&>>: Append redirect

COMMAND >/path/to/file.out 2> &1
COMMAND >>/path/to/file.out 2>> &1

>>x 2>>&1 Normal output to x error output to the same place as normal output (x)

Enter redirect:<

TR command: Convert or delete characters
TR [OPTION] ... SET1 [SET2] convert SET1 to SET2
-D Delete SET1 does not convert
Here documentation:<<
# cat << EOF input from terminal until EOF
# cat >/path/to/somefile << EOF

Pipeline:
COMMAND1 | COMMAND2 |  COMMAND3 | The execution of the previous command returns a value to the next command

Note: The last command executes in the child shell process of the current shell process;

Tee Command:
Tee [OPTION] ... [FILE] ...

Typically used in intermediate pipelines, the data entered into the process is output directly to a specified file, the other to the next command (through the pipeline), or directly to the screen

Text Processing tools: WC, cut, sort, uniq

WC Command: Statistics article details
WC [OPTION] ... [FILE] ...
-l:lines count rows
-w:words statistics of words
-c:characters count Words

Cut Command: Cut the article as required
Cut [OPTION] ... [FILE] ...
- D DELIMITER: Indicates delimiter
-F Fileds: Specifies that paragraphs are taken after splitting
#: Section # Fields
#,#[,#]: Discrete multiple fields, such as 1,3,6
#-#: Multiple consecutive fields, such as 1-6

Mixed use: 1-3,7
--output-delimiter=string

Sort command: Sort
Sort [OPTION] ... [FILE] ...
-F: Ignore character case
-R: Reverse order
- t DELIMITER: Field delimiter
-K #: Sort the specified fields as standard
-N: Sorting by numeric size
-u:uniq, after sorting, went heavy, near to heavy

uniq Command:
Uniq [OPTION] ... [FILE] ...
-C: Shows the number of repetitions of each line;
-D: Show only the rows that have been repeated;
-U: Displays only rows that have not been duplicated;

Linux Learning Diary--Basic Commands (4)--Text processing, redirection, pipelines