Declares which interpreter the user uses to interpret the shell program:
#!{
bin/bash,bin/csh,bin/sh,bin/tcsh,bin/ksh
}
implement:{
chmod 755 run.sh,./run.sh
sh ./run.sh
}
terminal(command) < [import] file, terminal(command) > [overwrite] file, terminal(command) >> [append] file
pipe (command result output | command start input)
Special characters{
$ variable name (reference variable)
#Comment , the first line is declared as a special case
Quotes [ "$`\ are strings except for escaping)" , 'all are strings' , `when the command is executed` ]
}
variable{
system variable {
$#(Number of command line arguments)
$n($1...parameter)
$0 (current program name)
$? (previous command/function return value)
$* (save all parameters in the form of parameters 1, 2...)
$@ (save all parameters in the form of parameters 1, 2...)
$$(PID of this program)
$!(last command PID)
}
environment ( set in ~/.bash_profile or ~/.bashrc ) {
export new environment variable name=""
The PATH command search paths are separated by colons. The difference from DOS is that the current directory is not in the search.
HOME The pathname of the user's home directory is the default parameter of the cd command
COLUMNS defines the length of the command line used in command edit mode
Editor default line editor
Visual default visual editor
The editor used by the Fcedit command fc
Histfile command history file
Histsize command history file contains the maximum number of commands
The maximum number of lines to include in the Histfilesize command history file
Ifs defines the separator used by the shell
Logname User login name
Mail points to a file whose modification time needs to be monitored by the shell
Mailcheck shell checks the cycle of mail files
Mailpath ? message to user
The pathname of the shell shell
Term terminal type
Tmout shell automatic exit time defaults to 0 seconds (forbids shell exit)
Prompt_command specifies the command to execute before the main command prompt
Ps1 main command prompt
Used when data input is required during the execution of the Ps2 command.
Command Prompt for Ps3 select
Ps4 debug command prompt
Manpath looks for man page paths separated by colons
Ld_library_path looks for library paths separated by colons
}
user{
The naming rules are the same as c, case sensitive
No declaration required, assignment is declaration
There must be no spaces at both ends of the equal sign
Reference variable [($variable name), (${variable name} is recommended to use this)]
[unset variable name] on the command line (clear variable assignment)
[readonly variable name] in the command line (defining constants, then assigning errors)
Variables are global by default
[local variable name] (local variable)
array {
array name=(v,v,v,v,v)
array name=(k=v,k=v,,,,,)
array name[index]=v
Reference array: ${array name[index]}
Number/array declaration (declare):
declare –(open)/+(close)[i(integer)/a(array)/f(function)/r(readonly)/x(defined as output variable through environment)]
}
The operator is basically the same as c
flow control {
-lt <
-the <=
-gt >
-ge >=
-eq =
-ne ！=
}
branch {
test Judgment expression / [expression] (will not produce standard output, must be judged by the return value)
test parameter [files already exist -f (normal file)/s (number of bytes>0)/r (readable)/w (writable)/x (executable)/d (directory)] file
Operator {-a/-o/!,\(,\) escape brackets with spaces on both ends}
If expression; then expression; fi
If expression; then expression; else expression; fi
If expression; then expression; elif then expression{1,} ;fi
Case “$#” in
0) Echo…;;
1) Echo…;;
*) Echo…;;
esac
}
cycle{
For variable name in list (as long as it is a list, such as: ls*.txt, many strings separated by spaces, seq 1 9=1~9
Do
Statement (quoting variable ${variable name})
$(expr $a \* $b) evaluates the expression or [] also evaluates the expression
Done
While expression;
Do statement;
Done
Until expression;
Do statement;
Done
Interrupt statement [break, continue, exit (termination of the program and return value can be obtained with $?, exit return value, so specify the return value)]
}
}
function{
Declare before available
Function name{…[return]}
Name(){…[return]}
call: name parameter....
recursion {
a(){
local i=$1
if [$i –eq 0]
then echo 1
else
local j=`expr $i-1`
local k=`a $j` write the function name in slash quotes to implement the call
echo `expr $i \* $k `
be
}
interact {
echo escape {
\aBell
\bbackspace
\c Force newline
\eExit
\fClear screen
\nNewline
\r Enter
\t tab
\v vertical tab
\\
\onnn Octal({0,3})
\nnn Octal({1,3})
\xhh hex({1,2})
echo “dfdfdg\nsdgfsg”
}
user input {
read{
-a name read input into name array
-d is used to truncate the input character default newline\n
-n read in n characters
-p show a prompt
-r Unescape \n Display normally
-s quiet mode input characters do not display
-t timeout read automatically stops
eg: read -p "Please enter a string:" str will input the string to the str variable
echo $str shows str
}