シェルスクリプトの基礎と原理入門

$PATH 
SHELL The shell currently in use
UID Current user environment {0|other number}={root|other user}
HOME Current user directory
PWD Current directory	
HISTFILE History command path
PS1 #[\u@\h \W]\$ user@hostname\directory\$

-eq Test if two integers are equal (equal)
-ne Tests if two integers are unequal (unequal)
-gt Tests if a number is greater than a number (greater than)
-lt tests if a number is less than a number (less than)
-ge Tests if a number is greater than or equal to 
-le Tests if a number is less than or equal to

=~ Test if a regular expression matches
-z "string" tests if the character is null, true if null, false if not e.g.: [ -z "" ] is vacuum then true
-n "string" detects if the character is not empty, true if not empty, false if not empty
characters compare size with [[ ]], than the first letter (a-zA-Z) are uppercase or are lowercase compare ascii value the larger the larger
There are upper case and lower case then A>a B>b but A is not greater than the case of b
[root@slave02 ~]# [[ "A" < "B" ]]
[root@slave02 ~]# echo $?
0
[root@slave02 ~]# [[ "a" < "b" ]]
[root@slave02 ~]# echo $?
0

-e: whether the file exists or not   
-b: test for block device files
-c: test for character device files
-f: test for normal files
-d: test for directories
-h: test if symbolic link file
-L: test if it is a symbolic link file
-p: test if it is a named pipe file
-S: test if it is a socket file
Permissions related.
-r read
-w write
-x execute
Special permissions
-g
-u
-k
etc.

Options.
-p: specify the prompt character
-t: specify how long to wait for the prompt (in seconds)

Multi-branching.
if [ condition ];then
	statement1
.....
elif [ condition2 ];then
statement2
....
else
statement3
....
fi

case $variable name in            
	'value1')                
		 statement                
		 ...                
 ;;            
	'value2')                
 		statement                
 		...                
 ;;            
*)                
 		statement                
 		...                
 ;;        
esac

Wildcard characters supported by #case.
    * //any length arbitrary character
    ?           //any single character of any length
    [] //any single character in the word range
   start|START //both options

First one.
for ((expr1;expr2;expr3)) # expr1: initial value condition  
								# expr2: the range of the loop to exit  
								# expr3: the value of the variable to use
{
loop body
}
for ((expr1;expr2;expr3));do            
Loop body
done
Second type.
for variables in list; do
loop
done

The while loop is used in scenarios where the number of loops is not known, note that there is an exit condition
while [ condition ];do
	statement
	.....
done

[root@slave02 ~]# cat script01.sh 
#! /bina=$1
b=$2
c=$3
num1=$[$a+$b+$c]
num2=$[$a-$b-$c]
num3=$[$a*$b*$c]
echo "$a + $b + $c" = $num1
echo "$a - $b - $c" = $num2
echo "$a * $b * $c" = $num3
awk "BEGIN{printf \"$a/$b/$c=%.2f\n\",$a/$b/$c}"
[root@slave02 ~]# source script01.sh 100 10 9
100 + 10 + 9 = 119
100 - 10 - 9 = 81
100 * 10 * 9 = 9000
100/10/9 = 1.11

[root@master ~]# cat test03.sh 
#! /binnums=99
read -p "please enter a number: " num
if [ $num -gt $nums ];then
        echo "The number is bigger"
elif [ $num -lt $nums ];then
        echo "number is small"
else
        echo "Guess right"
fi        
[root@master ~]# . test03.sh 
please enter a number: 10
The number is small
[root@master ~]# . test03.sh
please enter a number: 100
The number is too large
[root@master ~]# . test03.sh
please enter a number: 99
Guess right

#$0 is nginx itself $1 is the variable corresponding to the following start|stop|restart|status
[root@192 init.d]# pwd
/etc/init.d
[root@192 init.d]# cat nginx 
#! /bincase $1 in
        'start')
          /usr/local/nginx/sbin          ;;
        'stop')
          /usr/local/nginx/sbin/nginx -s stop
          ;;
        'restart')
        /usr/local/nginx/sbin/nginx -s stop
        /usr/local/nginx/sbin          ;;
        'status')
          num=$(ps -ef |grep -v 'grep'|grep -c nginx:)
          if [ $num -eq 0 ];then
                 echo "nginx is stopped" 
          else
                 echo "nginx is running"
          fi
          ;;
        *)
              echo "Usage: service $0 start|stop|restart|status"
          ;;          
esac
		# When judging the number of nginx processes, the service is considered to be on, otherwise it is considered to have failed

# create users user1-100
[root@master ~]# cat test05.sh 
#! /binfor (( i=1;i<=100;i++));do
        useradd user$i
        id user$i &>/dev        if [ $? -eq 0 ];then # As long as the user is judged successful, $? will only show 0, if it shows 0, it means execute the next command, otherwise it shows user and existence
                echo "success"
        else	
        		echo "user is exis"    
        fi
done

[root@slave02 ~]# cat which.sh 
#! /bins=0 # initial value 0
i=1 # value to judge, eventually stop at 100
while [ $i -le 100 ];do
s=$[$s+$i]			 
i=$[$i+1] #Self-incrementing number
done
echo $s
[root@slave02 ~]# source which.sh 
5050
						# If you enter a random number for calculation, change 100 to $1

1. general project or script, file, put in the appropriate location, easy to find
[root@slave02 tmp]# pwd
[root@slave02 tmp]# ls
apache
[root@slave02 apache]# ls
install_apache.sh soft
[root@slave02 soft]# ls
apr-1.7.0.tar.bz2 apr-util-1.6.1.tar.bz2 httpd-2.4.48.tar.bz2 httpd.service
[root@slave02 apache]# cat install_apache.sh #! /bin/bash echo "Welcome to this script" apachedir=/usr/local/apache if [ $UID -ne 0 ];then
        echo "Dude, please run as administrator"
fi
echo "Installing dependency packages... "
yum -y install epel-release bzip2 "@Development Tools" &>/devyum -y install openssl-devel pcre-devel expat-devel libtool gcc gcc-c++ make &>/devid apache &>/devif [ $? -ne 0 ];then
        useradd -r -M -s /sbin/nologin apache
fi
cd /tmp/apache/softtar -xf apr-1.7.0.tar.bz2
tar -xf apr-util-1.6.1.tar.bz2
tar -xf httpd-2.4.48.tar.bz2
sed -i '/ $RM "$cfgfile"/d' apr-1.7.0echo "Compiling and installing apr, please listen to the song and relax ....... " 
cd apr-1.7.0[ ! -d /usr/local/apr ]
if [ $? -eq 0 ];then
        . /configure --prefix=/usr/local/apr && make && make install &>/develse
        echo "apr is installed"
fi
cd ... /apr-util-1.6.1[ ! -d /usr/local/apr-util ]
if [ $? -eq 0 ];then
        . /configure --prefix=/usr/local/apr-util --with-apr=/usr/local/apr && make && make install &/develse
        echo "apr-util is installed"
fi
cd ... /httpd-2.4.48[ ! -d /usr/local/apache/ ]
if [ $? -eq 0 ];then
. /configure --prefix=$apachedir \
        --sysconfdir=/etc/httpd24 \
        --enable-so \
        --enable-ssl \
        --enable-cgi \
        --enable-rewrite \
        --with-zlib \
        --with-pcre \
        --with-apr=/usr/local/apr \
        --with-apr-util=/usr/local/apr-util/ \
        --enable-modules=most \
        --enable-mpms-shared=all \
        --with-mpm=prefork
        make && make install &>/develse
        echo "httpd is installed"
fi
cd
# Add judgment if it has an effect, ignore if it doesn't
echo "export PATH=$apachedir/bin:\$PATH" > /etc/profile.d/httpd.sh
ln -s $apachedir/include/ /usr/include/apache &>/devgrep 'apache/man' /etc/man_db.conf &>/dev
if [ $? -eq 1 ];then
        sed -i "20aMANDATORY_MANPATH $apachedir/man" /etc/ma