shell basic syntax

　　　　shell basic syntax

 

Shell pass parameters:

$#: the number of parameters passed to the script or function
$0: the name of the script itself
$n: the nth parameter of the script or function
$@: the list of all parameters passed to the script or function
$*: approximately equal to $@, a list of all parameters
$$: the PID of this script
$!: the PID of the last background command
executed $?: the return value of the last command executed

#!/bin/sh
echo "shell script name: $0"
echo "arg num: $#"
echo "args are: $@"
for arg in "$@"
do
    echo $arg
done
echo $*

 

1.for statement

#!/bin/sh

for file in $(ls /home/sfl/mytest/shell_test |grep sh)
do
    echo $file
done

for i in 0 1 2 3 4 5 6 7 8 9 # export 10th
 do
    echo $i
done

for i in  "0 1 2 3 4 5 6 7 8 9" #Only loop once, "" is a variable
 do
    echo $i
done

 

2. until statement

END_CONDITION=end

until [ "$var1" = "$END_CONDITION" ]
do
    echo "Input variable #1 "
    echo "($END_CONDITION to exit)"
    read var1
    echo "variable #1 = $var1"
    echo
done

exit 0

 

3.if statement

#!/bin/bash

echo "Input a number #1 "
read num #Get a parameter from the command line to num
echo "variable #1 = $num"
if [ $num -lt 60 ]
then
echo "you are not pass" 
elif [ $num -lt 70 ] && [ $num -ge 60 ] #Judgment of multiple conditions
then
echo "pass" 
elif [[ $num -lt 85 && $num -ge 70 ]] #If put together, pay attention to the double brackets, do not write it as [ $num -lt 85 && $num -ge 70 ]
then
echo "good" 
elif (( $num <= 100 )) && (( $num >= 85 )) #For those who have language foundation, this way of writing makes people feel very comfortable, don't forget the double parentheses
then
echo "very good"
else
echo "num is wrong"
fi #if must have an end tag, the root XML is very similar, if it is not closed, an error will be reported
exit 0

 

4. case statement

#!/bin/sh

#useage:./shell_case.sh start/stop/restart

case $1 in
start)
    echo "start ok"
;; #Note that it is a double semicolon
stop)
    echo "stop ok"
;;
restart)
    echo "restart ok"
;;
*)
    echo "no param"
;;
esac #watch out for closing tags

exit 0