Shell 스 크 립 트 빠 른 입문

#!/bin/bash

a=35
name="williams"
_o="o"
_ld='ld'
_old="$_o$_ld" #    `$`       （         ）

echo $name is $a years $_old #   

unset _o #     （  ）

williams is 35 years old

func1() {
    echo $1 # $1           
    echo $# # $#          
}

func2() {
    return $(($1+$2)) #                 （        ）
}

a=3
func1 "oops" 233 #     
func2 $a 2

echo $? #        /      

oops
2
6

txts=`ls | egrep *.\.txt` #   ls        ，  egrep  .txt  
#       txts=$(ls | egrep *.\.txt)
echo $txts #      txt   

text=`cat hello.txt` # => text      hello.txt     
username=`whoami` # => username          
echo $username # =>      ，  root

text1="hello,"
text2="world!"
echo -n $text1 > hello.txt #         (n      )
echo $text2 >> hello.txt #      hello.txt 

#!/bin/bash
# A + B Problem ~
read a
read b
c=$(($a+$b))
echo $a + $b = $c # => e.g. 1 + 3 = 4

text="eureka!"
text=`echo $text | tr 'a-z' 'A-Z'` #  tr             
echo $text

a=2
b=$(( ($a + 1) / 2 )) # => b = (2 + 1) / 2 = 1
rd=$((RANDOM % 100)) # => rd  0~99    
c=$(( $a > 1 )) # =>    a > 1 ，    1 (true)
d=$(expr $a + $b) # =>     $(($a + $b))

a=2; b=1; c=3; #               
str='ray-tracing'

[ $a -gt $b ] #        ， [$a -gt $b]      
echo $? #         $?   =>     0 (true)

[ $c -eq $c ] #     test $c -eq $c
echo $? #     0 (true)

[ $a -ne 1 -a $c -eq 3 ] #        a != 1 && c == 3
[ $a -ne 1 -o $c -ne 3 ] #        a != 1 || c != 3

[ $str != 'ray-tracing' ] #     1 (false)
[ $str = 'ray' ] #     1 (false)

[[ a + b = 3 && a != b ]] #     0 (true)
#       bash    

read a
echo -n $a is

b=$(( $a % 2 ))
if [ $b -eq 0 ]; then #    a      
	echo " even"
else
	echo " odd"
fi

if [ `whoami` = 'root' ]; then
	echo "and you are root ?"
elif [ `whoami` = 'phosphorus15' ]; then #     C    else if
	echo "seriously ?"
else
	echo "alright ~"
fi

if [ `whoami` = 'root' ]; then #     ！
else
	echo "oops !"
fi

a=1; b=0;
while [ $a -le 100 ]; do	#        while (( $a <= 100 )); do
	b=$(($a+$b))
	a=$(($a+1)) # bash      ((a++))
done
echo $b #     5050

a=1; b=0;
until [ $a -gt 100 ]; do
	b=$(($a+$b))
	a=$(($a+1))
done
echo $b #     5050

for i in Apple Juice Cake; do
	echo do you like $i ?
done

for j in `seq 0 3`; do
	echo $j
done

for k in `seq 65 70`; do
	echo $k | awk '{printf("%c", $1)}' #  ascii       
	# bash       printf,   printf \\x$(printf %x $k)
done

for c in {0..8..2}; do # 0~8       
	echo $c
done
#   ，      bash   

do you like Apple ?
do you like Juice ?
do you like Cake ?
0
1
2
3
ABCDEF

s=0
for i in `seq 1 100`; do #      1   100    
	s=$(($s+$i))
done
echo $s

for file in $(ls); do #       
        #   file         ，        
        if [ "$(file $file | grep -o directory)" != 'directory' ] 
        then
                cp $file "$file.bak" #   cp     
                echo backup $file
        fi
done

for((i=0;i<10;i++));
do
	echo $(expr 10 - $i) #     $((10 - $i))
done

a=(2 7 5 6 8 1 3 0 4 9)

b=({0..9}) # 0 1 2 3 4 5 6 7 8 9
c=({0..9..2} {1..9..2}) # 0 2 4 6 8 1 3 5 7 9

strs=("tomato" "potato" "onion" "lettuce" "okra")
misc=("str1" 1 "str2" 5 1)

echo ${a[0]} ${a[3]} # =>    2 6
echo ${b[@]} # =>    b       ，  ： 0 1 2 3 4 5 6 7 8 9

b[0]=10 #          10

echo ${b[@]} # =>    b       ，  ： 10 1 2 3 4 5 6 7 8 9
echo ${#misc[@]} # =>    misc    ，  5
echo ${strs[@]:1:3} # =>     1~3    ，  : potato onion lettuce

unset c[3] # =>       3    

for e in ${c[@]}; do
	echo -n "$e "
done
#              ，      0 2 4 8 1 3 5 7 9

#!/bin/sh
factorial() {
    if [ $1 -eq 0 ]; then return 1; fi
    s=1
    for i in `seq 1 $1`; do
    	s=$(($s*$i)) #   
    	trace[$(expr $i - 1)]=$s #       
    done
    echo calculation trace [${trace[@]}] #   
    return $s
}

if [ `whoami` = 'root' ]; then
	echo root is not allow to execute this script!
	exit
fi

if [ $# -lt 2 ]; then
	echo usage : sh fac.sh [n] [output] > /dev/stderr #       
elif [ $1 -lt 0 ]; then
	echo n cannot be less than zero ! > /dev/stderr
elif [ -z "$2" ]; then #       
	echo output file cannot be null ! > /dev/stderr
else
	factorial $1
	echo $1!=$? > "$2"
fi

phosphorus15@ubuntu:~/Documents$ sh fac.sh 
usage : sh fac.sh [n] [output]
phosphorus15@ubuntu:~/Documents$ sh fac.sh 1
usage : sh fac.sh [n] [output]
phosphorus15@ubuntu:~/Documents$ sh fac.sh 1 fac.txt
calculation trace [1]
phosphorus15@ubuntu:~/Documents$ file fac.txt
fac.txt: ASCII text
phosphorus15@ubuntu:~/Documents$ cat fac.txt
1!=1
phosphorus15@ubuntu:~/Documents$ sh fac.sh 5 fac.txt
calculation trace [1 2 6 24 120]
phosphorus15@ubuntu:~/Documents$ cat fac.txt
5!=120
phosphorus15@ubuntu:~/Documents$ sudo sh fac.sh 5 fac.txt
[sudo] password for phosphorus15: 
root is not allow to execute this script!