Unix Shell Programming Notes series (i)

I. Review of BASIC commands

Date//day and time displayed

WHO//view all users logged in to the system

echo//Display the input content

File Operation class

LS//List file list

CAT//Display file contents

Number of words in WC//statistics file

CP//Copy files

MV//File renaming

RM//Delete Files

Directory Operation class

PWD//show Current working directory

CD//change current working directory

mkdir//Create a directory

ln//Link file

Ln-s source file Destination file//link source file to destination file

RmDir//Delete directory

Character matching

*//Match 0 or more characters

? Match any one character

[ABC]//Match a single A or B or C

[0-9]//Match one character from 0 to 9, the ordinal of the first character of the specified range must be less than the next character

Example:

[a-np-z]*//matches a file name that starts with any letter from a-Z other than O

! Non -

Example:

[!a-z]//match any character except lowercase letters A to Z

*[!o]//matches any file name that does not end with a lowercase letter O

LS [a-z]*[0-9]//List of filenames that begin with a lowercase letter and end with a number

Standard input, Output

In the case of WHO, the WHO command writes a list of users logged into the system to a standard output device.

Input and output redirection

>//output redirect, overwrite existing content

>>//Append output redirection, do not overwrite existing content

Multiple files can be connected with cat (catenate)//After multiple files

Such as:

Cat a B >> c//Append the contents of A and B files to the C file

> File//Create an empty document named files with a length of 0 characters

Wc-l A//calculate the number of rows in a file

Pipeline

| Pipe character

W.H.O. | WC-L//The output of the WHO command is fed back to wc-l as input

Filter filters

Refers to the acceptance of input from the standard input, the input is processed, the results are written to the standard output of any program, such as SORT,WC, but LS does not count;

Standard error

2>//Standard error redirection

; Delimited commands, such as Date;pwd

&//For the back of the command, indicating background execution

PS//Display system running process information

Second, what is the shell?

Init->getty->login->sh

If a particular program is to be executed, the shell will search the disk and find the specified program, and when found, the shell requests the kernel to initialize the program, and then the shell goes to "sleep" until the program finishes executing.

Program Name parameter table

Shell role:

implementation procedures;

Interpreting programming languages;

Environmental control;

Pipe line Connection;

I/O redirection;

Variable and file name substitution;

The shell determines the starting and ending position of the program name and the starting and ending position of the parameter table by a specific character, with empty characters, tabs, and line Terminators (collectively, the whitespace characters);

The shell automatically ignores whitespace characters;

Unix Shell Programming Notes series (i)