PL00, System programming

$ echo $PATH

$ sudo echo $PATH

$ whereis [command]

$ which [command]

$ sudo which [command]

$ [command]           # $echo $PATH;whereis [command];which [command]  : through environmental variables
$ ./[command]         # pwd : on current directory 

$ pwd

$ cd ~     # move user directory
$ cd /     # move root directory
$ cd -     # move previous working directory

$ ls
$ ls -l
$ ls -a
$ ls -al
$ ls | grep [pattern]
$ ls -i

$ rm *                    # remove all files
$ rm [file_name]
$ rm -rf [folder_name]

$ cat [file_name]
$ cat [file_name] | sort {-r}
$ cat [file_name] | sort {-r} | grep [pattern]
$ head [file_name]
$ head -n[number_of_lines] [file_name]
$ tail [file_name]
$ tail -n[number_of_lines] [file_name]
$ more [file_name]                            # spacebar : next page, enter : next line
$ less [file_name]                        

$ grep [pattern] [file_name]         # search conformable pattern(string) in file
$ grep [pattern] *                   # search conformable pattern(string) only in present directory

$ grep -i [pattern] [file_name]      # search conformable pattern(string) in file, regardless of capital and small letter
$ grep -v [pattern] [file_name]      # search unconformable pattern(string) in file
$ grep -n [pattern] [file_name]      # search conformable pattern(string) in file, numbering line on results for searching
$ grep -l [pattern] [file_name]      # search conformable pattern(string) in file, displaying only file name including pattern

$ grep -c [pattern] [file_name]      # search conformable pattern(string) in file, displaying the number of consistant pattern line on a file 
$ grep -c [pattern] *                # search conformable pattern(string) in file, displaying the number of consistant pattern line on present directory 
$ grep -c [pattern] [folder_name]    # search conformable pattern(string) in file, displaying the number of consistant pattern line per file on a folder

$ grep -r [pattern] *                # search conformable pattern(string) in present directory including sub-directory
$ grep -E "[pattern_1]|[pattern_2]|[pattern_3]" [file_name]        # search pattern 1 or pattern 2 or pattern 3 in file

$ find / -name [file_name]                        # from root directory
$ find / -size [file_size]                        # from root directory
$ find / -name [file_name] -size [file_size]      # from root directory
$ find . -name [file_name]                        # from current directory
$ find . -size [file_size]                        # from current directory
$ find . -name [file_name] -size [file_size]      # from current directory

$ cmp [file_name] [file_name]
$ diff [file_name] [file_name]
$ file [file_name]

$ tar -cf [file_name.tar] a b c        # tie and zip a b c files 
$ tar -zcf [file_name.tar.gz] a b c    # zip a b c files 
$ tar -xvf [file_name.tar]             # unzip .tar
$ tar -zxvf [file_name.tar.gz]         # unzip .tar.gz
$ gzip [file_name]                     # file_name to file_name.gz
$ gzip -d [file_name].gz               # file_name.gz to file_name
$ zip -r [folder_name].zip folder_a    # zip folder_a folder_name.zip
$ unzip [file_name].zip
$ unzip [file_name].zip [path]

$ cat *.tar.gz.* | tar xvfz -       # unzip .tar.gz
$ cat *.tar.* | tar xvfz -          # unzip .tar

$ systemctl –-user

$ who
$ users
$ last

$ whoami

$ passwd [user_name]         # change or create
$ passwd -d [user_name]      # delete
$ passwd -u [user_name]      # unlock
$ passwd -l [user_name]      # lock

$ adduser [user_name]

$ su [user_name]        # change id including my present .bashrc, .profile files.
$ su - [user_name]       # change id excluding my present .bashrc, .profile files.

$ exit

$ usermod -a -G sudo [user_name]

$ groupadd [group_name]                     # create group
$ usermod -a -G [group_name] [user_name]    # add user to group
$ groups [user_name]                        # list of groups including user

$ chmod u=rwx, g=rw, o=rx [file_name]
$ chmod 765 [file_name]

$ chmod u=rwx, g=rw, o=rx [folder_name]
$ chmod -R u=rwx, g=rw, o=rx [folder_name]

$ chmod 765 [folder_name]
$ chmod -R 765 [folder_name]

$ chown [owner:owner_group] [file_name]

$ chown [owner:] [file_name]

$ chown [:owner_group] [file_name]
$ chgrp [owner_group] [file_name]

$ chown [owner:owner_group] [folder_name]
$ chown -R [owner:owner_group] [folder_name]

$ chown [owner:] [folder_name]
$ chown -R [owner:] [folder_name]

$ chown [:owner_group] [folder_name]
$ chown -R [:owner_group] [folder_name]
$ chgrp [owner_group] [folder_name]
$ chgrp -R [owner_group] [folder_name]

$ passwd root       : create password
$ passwd -d root    : delete password

$ su
$ su -l
$ su --login
$ sudo

$ echo [arbitary_stdout]

$ [command] > [file_name]        # overwrite with stdout
$ [command] 1> [file_name]       # overwrite with stdout
$ [command] 2> [file_name]       # overwrite with stderr

$ [command] >> [file_name]       # add text of stdout at the end
$ [command] 1>> [file_name]      # add text of stdout at the end
$ [command] 2>> [file_name]      # add text of stderr at the end

$ [command] 1>&2                 # stdout to stderr
$ [command] 2>&1                 # stderr to stdout
$ [command] >& [file_name]       # overwrite with stdout and stderr

$ [command] < [file_name] 
$ [command] < [file_name_1] > [file_name_2]

:/etc$ ls | grep issue

$ ./[file_name] &                       # execute on background
$ jobs                                  # list of process
$ bg                                    # re-execute last stoped process on background
$ bg [job_number_of_stoped_process]     # re-execute stoped process on background
$ kill -9 %[number_of_process]          # terminate process  

$ jobs
$ fg                                 # execute process denoted '+' on foreground
$ fg %[number_of_process]            # execute process corresponding number on foreground

$ ps             # displaying list of process for me
$ ps -a          # displaying list of process for all users(Select all processes except both session leaders and processes not associated with a terminal.)
$ ps -u          # displaying details about owner of process
$ ps -l          # displaying details about process
$ ps -x          # displaying deamon process
$ ps aux         # frequently used(-a, -u, -x)
                 # ps aux | more
                 # ps aux | grep [pattern]
                 # '$ top' or '$ htop' 
$ ps -e          # displaying list of all process
$ ps -f          # displaying relationship about process

$ kill -9 [pid]

$ top

$ top
$ htop
$ df -h
$ du -sh
$ vmstat
$ vmstat 1

$ service --status-all
$ service [process] start
$ service [process] status
$ service [process] stop
$ service [process] restart

$ copy [origin_file_name] [new_file_name]       # copy : different inode for origin file,
                                                #        be live after deleting origin file
$ ln [origin_file_name] [new_file_name]         # hard : equal inode for origin file,
                                                #        be live after deleting origin file
$ ln -s [origin_file_name] [new_file_name]      # soft : different inode for origin file,
                                                #        be die after deleting origin file

$ apt update
$ apt upgrade
$ apt install gcc
$ gcc --version

$ cat /proc/sys/kernel/pid_max

$ ps -fe

$ kill -l

$ ./loop &
$ ./sigkill 1806 2
$ ps

$ ./sigloop &
$ ./sigkill 1894 2
$ ps
$ kill -9 1894

#!/bin/bash

$ chmod u+x [file_name]

#!/bin/bash

# comment

#!/bin/bash

mysql_id='root'
mysql_directory='/etc/mysql'

echo $mysql_id
echo $mysql_directory

#!/bin/bash

daemons=("a" 2 "2" "c")
echo ${daemons[0]}             # a
echo ${daemons[1]}             # 2
echo ${daemons[2]}             # 2
echo ${daemons[2]}             # c
echo ${daemons[*]}             # a 2 2 c
echo ${daemons[@]}             # a 2 2 c
echo ${#daemons[*]}            # 4
echo ${#daemons[@]}            # 4

filelist1=( $(ls) )            # ls="file1" "file2" "" "" ...
                               # (ls)=("file1" "file2" "" "" ...)
                               # $(ls)=$("file1" "file2" "" "" ...)
                               
echo ${filelist1[*]}           # file1 file2 file3

filelist2=$(ls)             
echo ${filelist2[*]}            

#!/bin/bash

daemons=("httpd" "mysqld" "vsftpd")
echo ${daemons[1]}             # $daemons 배열의 두 번째 인덱스에 해당하는 mysqld 출력
echo ${daemons[@]}             # $daemons 배열의 모든 데이터 출력
echo ${daemons[*]}             # $daemons 배열의 모든 데이터 출력
echo ${#daemons[@]}            # $daemons 배열 크기 출력

filelist=( $(ls) )             # 해당 쉘스크립트 실행 디렉토리의 파일 리스트를 배열로 $filelist 변수에 입력
echo ${filelist[*]}            # $filelist 모든 데이터 출력

#!/bin/bash

num=`expr \( 3 \* 5 \) / 4 + 7`
echo $num

#!/bin/bash


# if 1
if [ conditional sentence ]
then
    [command]
fi

# if 2
if [ conditional sentence ]; then [command]; fi


# if else
if [ conditional sentence ]
then
    [command]
else
    [command]
fi

#!/bin/bash


# for 1
for [variable] in value1 value2 ...
do
    [command]
done

# for 2
for [variable] in value1 value2 ...; do [command]; done


# while
while [ conditional sentence ]
do
    [command]
done

#!/bin/bash

if [ -z $1 ]||[ -z $2 ]; then
    echo usage: $0 sourcedir targetdir
else
    SRCDIR=$1
    DSTDIR=$2
    BACKUPFILE=backup.$(date +%y%m%d%H%M%S).tar.gz
    if [ -d $DSTDIR ]; then
        tar -cvzf $DSTDIR/$BACKUPFILE $SRCDIR
    else
        mkdir $DSTDIR
        tar -cvzf $DSTDIR/$BACKUPFILE $SRCDIR
    fi
fi

#!/bin/bash

LOGDIR=/var/log
GZIPDAY=1
DELDAY=2
cd $LOGDIR
echo "cd $LOGDIR"

sudo find . -type f -name '*log.?' -mtime +$GZIPDAY -exec bash -c "gzip {}" \; 2> /dev/null
sudo find . -type f -name '*.gz' -mtime +$DELDAY -exec bash -c "rm -f {}" \; 2> /

$ cat /proc/ioports