내부 변수(Internal Variables)

PATH 설정에 . 이 없는 이유

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# PATH=.:$PATH
# echo $PATH
.:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/java/bin:/root/bin

# useradd linux
# install /dev/null ~linux/ls
# cat << EOF >> ~linux/ls
> #!/bin/sh
> 
> echo rm -rf /
> EOF
# cd ~linux
# ls
rm -rf /
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IFS 환경변수

고전해킹의 일종

google.com 검색

http://www.linuxlab.co.kr/docs/12-3.htm
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# echo $PPID
9624
[root@fw ~]# ps
  PID TTY          TIME CMD
 9632 pts/4    00:00:00 bash
 9712 pts/4    00:00:00 ps
[root@fw ~]# LANG=C
[root@fw ~]# pstree -p | grep $PPID
        |-sshd(31905)---sshd(9624)---bash(9632)-+-grep(9714)
[root@fw ~]# pstree -p | grep 9624 
        |-sshd(31905)---sshd(9624)---bash(9632)-+-grep(9716)
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PS1
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PS2

# ls \
> -l \
> -a \
> -i

# echo $PS2
>
# PS2="----> "
# ls \
----> -a
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PS3 : 3차 프롬프트로 select 루프문에서 표시된다

[root@fw ~]# select vegetable in "콩" "당근" "감자" "양파" "순무"
----> do
---->   echo
---->   echo "제일 좋아하는 야채가 $vegetable 이네요."
---->   echo "깔깔~~"
---->   echo
---->   break  # 여기에 'break'가 없으면 무한 루프를 돕니다.
----> done
1) 콩
2) 당근
3) 감자
4) 양파
5) 순무
#? 
1) 콩
2) 당근
3) 감자
4) 양파
5) 순무
#? 
[root@fw ~]# echo $PS3

[root@fw ~]# PS3="<--->"
[root@fw ~]# select vegetable in "콩" "당근" "감자" "양파" "순무"
----> do
---->   echo
---->   echo "제일 좋아하는 야채가 $vegetable 이네요."
---->   echo "깔깔~~"
---->   echo
---->   break  # 여기에 'break'가 없으면 무한 루프를 돕니다.
----> done
1) 콩
2) 당근
3) 감자
4) 양파
5) 순무
<--->
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PS4

[root@fw ~]# PS4="dkdkdk"
[root@fw ~]# ./testps4.sh 
+ A=10
+ B=20
+ C=30
+ echo 10
10
+ echo 20
20
+ echo 30
30
[root@fw ~]# export PS4="dkdkdk"
[root@fw ~]# ./testps4.sh 
dkdkdkA=10
dkdkdkB=20
dkdkdkC=30
dkdkdkecho 10
10
dkdkdkecho 20
20
dkdkdkecho 30
30

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TMOUT, PATH, IFS 
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보안과 직접적으로 연관되어 있는 환경변수들
TMOUT, PATH, IFS, HISTFILE, HISTFILESIZE, HISTSIZE
TMOUT : /etc/profile  TMOUT=300; export TMOUT
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