shell note

# double quote
name="hel\"lo"

# single quote
name='hello'

name="hello${str1}"

name="hello"${str2}"world"

name="hello${str}world"

# for loop
for file in `ls`; do
    echo ${file}
done

# count string total char
echo ${#str1}

# string slice
echo ${str:4:2}

echo "hello" "world"

# find index
echo `expr index ${str} sub`

# array
arr=("he" "llo" "wo" "rld")

# asign to array
arr[0]="yesido"

# no boundry limit
arr[90]="lastone"

echo ${arr[90]}

# get all
echo ${arr[@]}

# count array total element
length=${#arr[@]}

# count array total element
echo ${#arr[*]}

# count string total char
echo ${#arr[2]}

# comment
# this is comment

# filename of this sh
$0

# nth argument
$1 $2 $3 $4

# count total argument
$#

# current process id
$$

# last deamon process id
$!

# last process return value
$?

# all arguments in a string
$*

# all arguments in a array
"$*"

arr2=(a b ccc DDD "yes" 'sss' 12)
echo ${arr2[@]}

# space!!
res=`expr 2 + 2`

res=`expr 7 \* 89`

# + - \* / % == !=

# space!!
if [ ${a} == ${b} ]
then
    #
fi

# compare
# -eq -nq -gt -lt -ge -le

# logical
# ! -o -a

# logical
# && ||

# check
# -d -b -c -f -p -r -w -x -s -e

if [ -e "/etc/apt/sources.list" ]

path="/etc/src"

if [ -d $path ]

echo "this is string"

echo this is string

# read stdin to string
read line

echo "new line is ${line}"

# -e enable escape
echo -e "firstline\nsecondline"

# \c disable change line
echo -e "lastline\c"

# > redirect stdout, < redirect stdin
echo "anything" > filename.suffix

# tee redirect to file also to stdout
echo "anything" | tee filename.suffix

# single quote, disable variable parse and escape
echo 'something&{name}$n\ame'

echo `date`

# printf usage
# printf format-string arguments

printf "hello world\n"

printf "%-10s%5s\n" "hello" "worlds"

# %-10s %4.2f %2s %d

# \a \c \t \n \\ \v \f \b

# flow control
if test 1 == 2

if test $num1 -eq ${num2}

if test -d file

if [ 1 == 2 ]
then
    echo 1
    echo 2
    echo "eq"
fi

# single line, ;
if test 1 -eq 2; then echo "eq"; fi

# if then elif else fi
if [ $a -gt $b ]
then
    echo $a
elif [ $a -ge 7 ]
then
    echo 7
else
    echo "none"
fi

echo $[ 2+ 4]

echo `expr 2 + 4`

# for in do done
for num in 1 2 3 4 5; do
    echo $num
done

# while do done
while test 1 == 2; do echo hello; done;

i=0
while test $i -le 5
do
    echo $i
    let "i++"
done

# forever loop
while :
do
    echo "loop forever"
done

while true
do
    echo "loop forever"
done

# util do done
util test 1 == 2
do
    echo "1 will never equal to 2"
done

# case
case $value in
    1) echo 1
    ;;
    "hello") echo "he"; echo "llo"
    ;;
    *) echo "handle default"
    ;;
esac

# break continue -> for while-do util-do

# function definition
func_name(){
    echo $1 $2 $3 $# $*
    return 255
}

# call function
func_name 1 2 3 4 5

# get function result
echo $?

echo "hello" > filename

# redirect to file, add
echo "add" >> filename

# > >> < << >& <&

# 0 1 2 stdin stdout stderr

# command < input > output
# command > file 2>1
# command > file 2>&1

wc -l << EOF
    "doc"
EOF

# discard stdout
echo "anything" > /dev/null

# marge stderr to stdout, then discard stdout
echo "any stdout any error" > /dev/null 2>&1

# include external sh
. /path/to/external/sh