기본2

TIP

• 보안 관련

  • eval 사용하지 말기

  • $PATH 변수 보호하기

  • 사용자 input은 항상 quote 하기

  • SUID 에 대해 걱정 말기. (쉘 스크립트에 의해 이미 사용할 수 없음)

if 문 짧게 개선하기

# BEFORE
if [ -z $1 1]
then
  echo no argument provided
exit 1
elif [ ! -e $1]
then
  echo $1 does not exist
exit 2
elif [ -d $1 ]
then
  echo $1 is a directory
elif [ ! -f $1 ]
then
  echo $1 is a not a directory and not a file
elif [ -x $1]
then
  echo $1 is an executable file
elif grep '#!/bin/bash' $1
then
  echo $1 is a non-executable bash script
chmod +x $1
else
  echo I don\'t know what this is
fi

# AFTER
[ -z $1 ] && echo no argument provided && exit 1
[ ! -e $1 ] && echo $1 does not exist && exit 2
[ -d $1 ] && echo $1 is a directory && exit
[ ! -f $1 ] && echo $1 is not a directory or file && exit
[ -x $1 ] && echo $1 is executable && exit
grep '#!/bin/bash' $1 && echo $1 is a non-executable shell script && chmod +x $1 && exit
echo I don\'t know what this is

패턴 매칭

BLAH=rababarabarabarara
clear
echo BLAH is $BLAH
echo 'the result of ##*ba is' ${BLAH##*ba}
echo 'the result of #*ba is' ${BLAH#*ba}
echo 'the result of %ba* is' ${BLAH%%ba**}
echo 'the result of %ba* is' ${BLAH%ba*}

## ————————— 결과 —————————
#BLAH is rababarabarabarara
#the result of ##*ba is rara
#the result of #*ba is barabarabarara
#the result of %ba* is ra
#the result of %ba* is rababarabara

declare: 변수 read-only로 만들기

• 특정 입력이 주어져야 할때 주로 사용

declare -r n=10
echo "n=$n"
n=20
echo "n=$n"

# ————————— 결과 —————————
#n=10
#advanced.sh:8: read-only variable: n

select

echo 'choose a directory: '
select dir in /bin /usr /etc
do
  if [ -n "$dir" ] # only continue if user has selected something
   then
    DIR=$dir
    echo you have selected $DIR
    export DIR
    break
  else
    echo invalid choice
  fi
done

## ————————— 결과 —————————
#choose a directory:
#1) /bin  2) /usr  3) /etc
#?# 4
#/Users/yoochulkim/IdeaProjects/SelfStudy/Bash/advanced.sh:14: command not found: x
#invalid choice
#?# 1
#/Users/yoochulkim/IdeaProjects/SelfStudy/Bash/advanced.sh:14: command not found: x
#you have selected /bin

while

• 남은 시간, 늦은 시간 카운트

COUNTER=$1
COUNTER=$(( COUNTER * 60 )) # 1 -> 60 (즉, 1분으로 변경)

mineen(){
  COUNTER=$(( COUNTER - 1))
  sleep 1
}

while [ $COUNTER -gt 0 ]
do
  echo you still have $COUNTER seconds
  mineen
done

[ $COUNTER = 0 ] && echo out of time && mineen
[ $COUNTER = "-1" ] && echo you are one second late && mineen

while true
do
  echo you are ${COUNTER#*-} seconds late
  mineen
done

## ————————— 결과 —————————
#you still have 60 seconds
#...
#out of time
#...
#you are 2 second late
#...

for: 현재 디렉토리 모드 출력

for i in *; do echo $i; done

case:

echo "how are you?"
read answer
answer=`echo $answer | tr a-z A-Z` # 소문자 -> 대문자 변경
[ -z $answer ] && exit 1 # empty 확인

case $answer in
 GOOD)
   echo "nice!";;
 BAD)
   echo "too bad for you";;
 *)
   echo "I don't understand your answer";;
esac

# ————————— 결과 —————————
#how are you?
#good
#nice!

array

array=(one two three four [5]=five)

echo "Array size: ${#array[*]}"

echo "Array items:"
for item in ${array[*]}
do
  printf "  %s\n" $item
done

echo "Array items and indexes:"
for index in ${!array[*]}
do
  printf "%4d: %s\n" $index ${array[$index]}
done

# ————————— 결과 —————————
#Array size: 5
#Array items:
#  one
#  two
#  three
#  four
#  five
#Array items and indexes:
#   0: one
#   1: two
#   2: three
#   3: four
#   5: five

Random 숫자 출력

for (( i = 0; i < 100; i++ )); do
    echo $((RANDOM%3))
done

Function 이용 구구단 만들기

NUMBER=0
NUMBER1=0
NUMBER2=0
CORRECT_ANSWER=0
ANSWER=0
CORRECT=0
MAX_TRIES=3

function generate_question(){
  generate_numbers
  determine_operation
  QUESTION="$NUMBER1 $OPERATION $NUMBER2"
}
function generate_numbers(){
  generate_number
  NUMBER1=$NUMBER
  generate_number
  NUMBER2=$NUMBER
}
function generate_number(){
  NUMBER=$((RANDOM%10+1))
}
function determine_operation(){
  RAND=$((RANDOM%3))
  case $RAND in
    0) OPERATION='*';;
    1) OPERATION='+';;
    2) OPERATION='-';;
  esac
}

function calculate_answer(){
  CORRECT_ANSWER="$(echo "$QUESTION" | bc)" # echo 1 + 2 | bc -> 3 나옴
}

function check_answer(){
  if [ $ANSWER -eq $CORRECT_ANSWER 2>/dev/null ] ; then
      echo "Correct!"
      CORRECT=1
    if [ $TRY -ne 1 ]; then
      write_log
    fi
  else
    if [ $TRY -eq $MAX_TRIES ]; then
      TRY=$(($MAX_TRIES +1))
      write_log
      echo "The correct answer was  "
      echo "Let's try the next one (press any key)"
      read
    else
      TRY=$(($TRY+1))
      echo "Nope sorry, please try again... (attempt $TRY)"
    fi
  fi
}

function init_log(){
  echo "------------- Log for $(date +%d-%m-%Y' '%H:%M)" >> log
}

function write_log(){
  if [ $TRY -le $MAX_TRIES ]; then
    echo "Answer to $QUESTION ($CORRECT_ANSWER) given in $TRY tries" >> log
  else
    echo "Answer to $SQUESTION ($CORRECT_ANSWER) not given" >> log
  fi
}

while true
do
  CORRECT=0
  TRY=1
  generate_question
  calculate_answer
  echo "How much is $QUESTION ? (attempt $TRY)"
  #echo "(Correct answer is $CORRECT_ANSWER)"
  while [ $CORRECT -ne 1 ] && [ $TRY -le $MAX_TRIES ]
  do 
    read "ANSWER" # 보안상 사용자 입력은 꼭 quote 하기
    check_answer
  done
done

exit 0

# ————————— 결과 —————————
#How much is 3 - 7 ? (attempt S1)
#-4
#Correct!
#(Correct answer is -4)
#How much is 8 + 5 ? (attempt S1)
#13
#Correct!
#(Correct answer is 13)
#How much is 2 * 9 ? (attempt S1)
#18
#Correct!