（7） Process control

#!/bin/bash
# shell The process control of cannot be empty 
:<<EOF
<?php
if (isset($_GET["q"])) {
    
    search(q);
}
else {
    
    //  Not doing anything 
}
 stay  sh/bash  You can't write that in , If  else  Branch has no statement execution , Don't write this  else.
EOF

# 1. if else

# 1.1 if  grammar 
:<<EOF
if condition
then
    command1
    command2
    ...
    commandN
fi

 Write in a line （ For terminal command prompt ）
if [ $(ps -ef | grep -c "ssh") -gt 1 ]; then echo "true"; fi
EOF

# 1.2 if else  grammar 
:<<EOF
if condition
then
    command1
    command2
    ...
    commandN
else
    command
fi
EOF

# 1.3 if else-if else  grammar 
:<<EOF
if condition1
then
    command1
elif condition2
then
    command2
else
    commandN
fi
EOF

# 1.4  example 
a=10
b=20
if test ${
    a} -eq ${
    b} # if [ $a= $b]
then
  echo "a  and  b equal "
elif test ${
    a} -gt ${
    b} # elif [ $a -gt $b ]
then
  echo "a  Greater than  b"
elif test ${
    a} -lt ${
    b} # [ $a -lt $b ]
then
  echo "a  Less than  b"
else
  echo " Not qualified "
fi

# 2. for  loop 
#  grammar 
:<<EOF
for var in item1 item2 ... itemN
do
  command1
  command2
  ...
  commandN
done

#  Write in a line 
for var in item1 item2 ... itemN; do command1; command2… done;
EOF

for loop in 1 2 3 40
do
  echo "The value is: ${loop}"
done

for str in This is a string.
do
  echo ${
    str}
done

# 3. while  sentence 
# 3.1  grammar 
:<<EOF
while condition
do
  command
done
EOF

#  example 
num1=1
while (( $num1<=5))
do
  echo "${num1}"
  let "num1++"
done
#  The above example uses  Bash let  command , It is used to execute one or more expressions ,
#  There is no need to add  $  To represent a variable 

# 3.2  Read keyboard information 
echo -n ' Enter your favorite website name : ' #  When -n  Options , Then cancel the trailing newline 
while read FILM
do
    echo " Yes ！$FILM  It's a good website "
    break
done

# 3.3  Infinite loop 
:<<EOF
#  The first one is 
while :
do
    command
done

#  The second kind 
while true
do
    command
done

#  The third kind of 
for (( ; ; ))
EOF

# 4. until  loop 
# until  Loop through a series of commands until the condition is  true  Stop when .
# until  Circulation and  while  The cycle is the opposite of the way it's handled .

# 4.1  Grammar format 
:<<EOF
until condition
do
  command1
done
EOF

#  example 
a=0
until [ ! $a -lt 10 ]
do
   echo $a
   a=`expr $a + 1`
done

# 5. case ... esac
# case ... esac  Select multiple statements for , And in other languages  switch ... case  Statements like ,
#  It's a multi branched selection structure , Every  case  The branch begins with a right parenthesis , Use two semicolons  ;;  Express  break, The end of execution ,
#  Jump out of the whole  case ... esac  sentence ,esac（ Namely  case  In turn, ） As the closing tag .
#
#  It can be used  case  Statement matches a value with a pattern , If the match is successful , Execute the matching command .

# 5.1  grammar 
:<<EOF
case  value  in
 Pattern 1)
    command1
    command2
    ...
    commandN
    ;;
 Pattern 2）
    command1
    command2
    ...
    commandN
    ;;
esac
EOF

#  Value must be followed by word  in, The first mock exam must be closed with right brackets. .
#  Value can be variable or constant , Match found that after the first mock exam meets a certain pattern, , During this period, all commands are executed until  ;;.
#  Value will detect every matching pattern . Once the patterns match , After the corresponding command of matching mode is executed, other modes will not be continued .
#  If there is no matching pattern , Use the asterisk  *  Capture the value , Then execute the following command .

#  example 1—— The number 
echo " Input 1-4 Integer between "
echo " The value you entered is ："
read num11
case $num11 in
1) echo " You entered 1"
  ;;
2) echo " You entered 2"
  ;;
3) echo " You entered 3"
  ;;
4) echo " You entered 4"
  ;;
*) echo " You entered other numbers "
  ;;
esac
#  example 2—— character string 
site="runoob"
case "${site}" in
   "runoob") echo " Novice tutorial "
   ;;
   "google") echo "Google  Search for "
   ;;
   "taobao") echo " TaoBao "
   ;;
esac

# 6  Out of the loop 
# 6.1 break： Out of the loop 
# 6.2 continue： Jump out of current loop