• prompts
  • settings
  • colors
  • functions
• character
  • metacharacter
• process substitution
  • example: run script without download
  • example: merge lines of file
    • nstalling tools via running random scripts from unknown sites
  • strace
• basic commands
  • du
  • sort
    • sort result via human-readable format
  • others
    • you have new mail
    • crontab
• tricky
  • unicode
  • useful functions
  • search manual page

prompts

settings

[!NOTE|label:inputrc]

• * iMarlso: inputrc
• * marslo/mylinux/inputrc

# https://marslo.github.io/ibook/screenshot/colors/ansi/color-formatting.png
fgc=$(RGBcolor 5 6 8)                             # 240;  fgc=$(RGBcolor 5 6 5)  # 237
COL_SD_GREEN='\[\033[32;2m\]'                     # COL_SD_GREEN='\[\033[2;32m\]'
COL_IF_SL_RED='\[\033[0\;31m\]'
COL_DEFAULT="\[\033[38;5;${fgc}m\]"               # "\[$(tput setaf ${fgc})\]"; $"\e[38;5;${fgc}m";
COL_IF_DEFAULT="\[\033[38\;5\;${fgc}m\]"          # COL_IF_DEFAULT="\[\033[1\;38\;5\;${fgc}m\]"  | COL_IF_DEFAULT="${COL_IF_SD_GREEN}"
COL_RESET='\[\033[1m\]'                           # COL_RESET="\[$(tput sgr0)\]" | COL_RESET='\[\033[1m\]'
COL_NONE='\[\033[0m\]'                            # COL_NONE='\[\033[38;5;3m\]'

PS1="\\n${COL_RESET}${COL_DEFAULT}╭╶ (\\u@\\h${COL_RESET} "
PS1+="${COL_SL_RED}\\w${COL_RESET}${COL_DEFAULT}) "
PS1+="\$(__git_ps1 \"- (${COL_SD_GREEN}%s${COL_NONE}${COL_DEFAULT}) \")${COL_RESET}"
PS1+="${COL_DEFAULT}\`if [ \$? = 0 ]; then echo ${COL_IF_DEFAULT}\⏵; else echo ${COL_IF_SL_RED}\⏵; fi\`${COL_RESET}"
PS1+="\\n${COL_DEFAULT} \$ ${COL_RESET}"
PS1+="${COL_NONE}"
PS2="${COL_DEFAULT}  -> ${COL_RESET}${COL_NONE}"
PS4=' ${BASH_SOURCE}:$FUNCNAME:$LINENO: '

PS1="\\n${COL_RESET}${COL_DEFAULT}╭╶ (\\u@\\h${COL_RESET} "
PS1+="${COL_SL_RED}\\w${COL_RESET}${COL_DEFAULT}) "
PS1+="\`__git_ps1 '- (%s) '\`"
PS1+="${COL_RESET}${COL_DEFAULT}->${COL_RESET}"
PS1+="\\n${COL_DEFAULT}╰╶ ${COL_RESET}"
PS1+="\`if [ \$? = 0 ]; then echo ${COL_IF_DEFAULT}\\$; else echo ${COL_IF_SL_RED}\\$; fi\` ${COL_RESET}"
PS1+="${COL_NONE}"
# PS2="${COL_DEFAULT} |-> ${COL_RESET}${COL_NONE}"
PS2="${COL_DEFAULT}  -> ${COL_RESET}${COL_NONE}"
PS4=' ${BASH_SOURCE}:$FUNCNAME:$LINENO: '

export PS1 PS2 PS4

UMARK='\[\033(0\]l\[\033(B\]'
DMARK='\[\033(0\]m\[\033(B\]'
LMARK='\[\033(0\]q\[\033(B\]'

COL_SL_GREEN='\[\033[32;0m\]'
COL_SD_GREEN='\[\033[32;2m\]'                     # COL_SD_GREEN='\[\033[2;32m\]'
COL_SD_YELLOW='\[\033[2;33m\]'
COL_SL_YELLOW='\[\033[0;33m\]'
COL_B_YELLOW='\[\033[2;33m\]'
COL_IF_SD_YELLOW='\[\033[2\;33m\]'

COL_D_BLACK='\[\033[30;1m\]'
COL_L_BLACK='\[\033[30;0m\]'
COL_SD_BLACK='\[\033[1;30m\]'
COL_SL_BLACK='\[\033[0;30m\]'
COL_SD_RED='\[\033[1;31m\]'
COL_SL_RED='\[\033[0;31m\]'
COL_SD_BLUE='\[\033[1;34m\]'
COL_SL_BLUE='\[\033[0;34m\]'
COL_L_RED='\[\033[31;0m\]'
COL_D_RED='\[\033[31;1m\]'

COL_IF_D_BLACK='\[\033[30\;1m\]'
COL_IF_L_BLACK='\[\033[30\;0m\]'
COL_IF_SD_BLACK='\[\033[1\;30m\]'
COL_IF_SL_BLACK='\[\033[0\;30m\]'
COL_IF_SL_YELLOW='\[\033[0\;33m\]'
COL_IF_D_RED='\[\033[31\;1m\]'
COL_IF_SD_RED='\[\033[1\;31m\]'
COL_IF_SL_RED='\[\033[0\;31m\]'
COL_IF_SL_GREEN='\[\033[0\;32m\]'
COL_IF_SD_GREEN='\[\033[2\;32m\]'
COL_IF_SL_BLUE='\[\033[0\;34m\]'
COL_IF_SD_BLUE='\[\033[1\;34m\]'

if [ -z "$DISPLAY" ]; then
  export PS1="\n${COL_D_BLACK}┌─ (\u@\h ${COL_RESET} ${COL_D_RED}\w${COL_RESET}${COL_D_BLACK}) ->${COL_RESET}\n${COL_D_BLACK}└─ ${COL_RESET}\`if [ \$? = 0 ]; then echo ${COL_SD_BLACK}\\$ ${COL_RESET}; else echo ${COL_SD_RED}\\$ ${COL_RESET}; fi\`${COL_NONE}"
  export PS2="${COL_D_BLACK} -> ${COL_RESET}${COL_NONE}"
else
  export PS1="\n${COL_D_BLACK}${UMARK}${LMARK} (\u@\h ${COL_RESET} ${COL_D_RED}\w${COL_RESET}${COL_D_BLACK}) ->${COL_RESET}\n${COL_D_BLACK}${DMARK}${LMARK} ${COL_RESET}\`if [ \$? = 0 ]; then echo ${COL_SD_BLACK}\\$ ${COL_RESET}; else echo ${COL_SD_RED}\\$ ${COL_RESET}; fi\`${COL_NONE}"
  export PS2="${COL_D_BLACK} ->${LMARK} ${COL_RESET}${COL_NONE}"
fi

# for mac os -> Solarized Dark
export PS1="\n${COL_DEFAULT}┌─ (\u@\h${COL_RESET} ${COL_SD_RED}\w${COL_RESET}${COL_DEFAULT}) ->${COL_RESET}\n${COL_DEFAULT}└─ ${COL_RESET}\`if [ \$? = 0 ]; then echo ${COL_IF_DEFAULT}\\$ ${COL_RESET}; else echo ${COL_IF_SL_RED}\\$ ${COL_RESET}; fi\`${COL_NONE}"

colors

• Bash tips: Colors and formatting (ANSI/VT100 Control sequences)

  # https://misc.flogisoft.com/bash/tip_colors_and_formatting
  #  ----+---+---+----+---+----       --------+--------     ----+------+------
  # | ⌌・| ⠋ | ⌜ | ╭╶ | ┌ | ┌─ |    | 0\;xxm | Normal |    | \e | \033 | \x1B |
  # | ⌎・| ⠦ | ⌞ | ╰╶ | └ | └─ |    | 1\;xxm | Bright |     ----+------+------
  #  ----+---+---+----+---+----      --------+--------
  #
  #  ---+--------------++---------------------++----------------------+    +-----------------
  # | # |  color name  ||      foregrand      ||      background      |    |   attribute     |
  #  ---+--------------++---------------------++----------------------+    +---+-------------
  # | 9 | Default      ||      \e[0;39m       ||       e[0;49m        |    | 0 | Normal      |
  # | 0 | Black        || \e[0;30m |          || \e[0;40m |           |    | 1 | Bold        |
  # | 1 | Red          || \e[0;31m |          || \e[0;41m |           |    | 2 | Faint       |
  # | 2 | Green        || \e[0;32m |          || \e[0;42m |           |    | 3 | Italic      |
  # | 3 | Yellow       || \e[0;33m |          || \e[0;43m |           |    | 4 | Underline   |
  # | 4 | Blue         || \e[0;34m |          || \e[0;44m |           |    | 5 | Slow Blink  |
  # | 5 | Purple       || \e[0;35m |          || \e[0;45m |           |    | 6 | Rapid Blink |
  # | 6 | Cyan         || \e[0;36m |          || \e[0;46m |           |    | 7 | reverse     |
  # | 7 | Light Gray   || \e[0;37m |          || \e[0;47m |           |     ---+-------------
  # | 0 | Dark Gray    || \e[1;30m | \e[0;90m || \e[1;40m | \e[0;100m |     ---------------------
  # | 1 | Light Red    || \e[1;31m | \e[0;91m || \e[1;41m | \e[0;101m |    |       others        |
  # | 2 | Light Green  || \e[1;32m | \e[0;92m || \e[1;42m | \e[0;102m |     -------------+-------
  # | 3 | Light Yellow || \e[1;33m | \e[0;93m || \e[1;43m | \e[0;103m |    | color none  | \e[0m |
  # | 4 | Light Blue   || \e[1;34m | \e[0;94m || \e[1;44m | \e[0;104m |    | color reset | \e[1m |
  # | 5 | Light Purple || \e[1;35m | \e[0;95m || \e[1;45m | \e[0;105m |     -------------+-------
  # | 6 | Light Cyan   || \e[1;36m | \e[0;96m || \e[1;46m | \e[0;106m |     ----------------+---------------------------------
  # | 7 | White        ||      \e[0;97m       ||      \e[0;107m       |    | \[\e[xx;0m]\]  | system color                    |
  #  ---+--------------++---------------------++----------------------     | \[\e[xx\;0m]\] | system color in ``              |
  # |   |              ||  \e[38;5;{0..255}m# ||  \e[48;5;{0..255}m#  |    | \[\e[0;xxm]\]  | profile color (solarized)       |
  #  ---+--------------++---------------------++----------------------     | \[\e[0\;xxm]\] | profile color (solarized) in `` |
  #                                                                         ----------------+---------------------------------
  #  ------------+-------------------------------------------------------   ----------------+-------------------------------
  # |                   256 colors standard format                       | |                   comments                     |
  #  ------------+-------------------------------------------------------   ----------------+-------------------------------
  # | attributes | 0 1 2 3 4 5 6 7                                       | | COL_NONE       | no color                      |
  # | foregrand  | {0..255}                                              | | COL_RESET      | reset color                   |
  # | background | {30..37} {90..97} 39                                  | | COL_DEFAULT    | default color                 |
  #  ------------+-------------------------------------------------------  | COL_IF_DEFAULT | default color in if-statement |
  # | usage : \e[${attributes};{background};5;${foreground}m <str> \e[0m |  ----------------+-------------------------------
  #  ------------+-------------------------------------------------------
  #
  # Solarized color table from http://ethanschoonover.com/solarized.
  #
  # | SOLARIZED | HEX     | ANSI      | TERMCOL   | cmd.exe     | PowerShell  | ColorTable | DWORD    |
  # |-----------|---------|-----------|-----------|-------------|-------------|------------|----------|
  # | base03    | #002b36 | ESC[0;30m | brblack   | Black       | Black       | 00         | 00362b00 |
  # | base02    | #073642 | ESC[1;30m | black     | Gray        | DarkGray    | 08         | 00423607 |
  # | base01    | #586e75 | ESC[0;32m | brgreen   | Green       | DarkGreen   | 02         | 00756e58 |
  # | base00    | #657b83 | ESC[0;33m | bryellow  | Yellow      | DarkYellow  | 06         | 00837b65 |
  # | base0     | #839496 | ESC[0;34m | brblue    | Blue        | DarkBlue    | 01         | 00969483 |
  # | base1     | #93a1a1 | ESC[0;36m | brcyan    | Aqua        | DarkCyan    | 03         | 00a1a193 |
  # | base2     | #eee8d5 | ESC[0;37m | white     | White       | Gray        | 07         | 00d5e8ee |
  # | base3     | #fdf6e3 | ESC[1;37m | brwhite   | BrightWhite | White       | 15         | 00e3f6fd |
  # | yellow    | #b58900 | ESC[1;33m | yellow    | LightYellow | Yellow      | 14         | 000089b5 |
  # | orange    | #cb4b16 | ESC[0;31m | brred     | Red         | DarkRed     | 04         | 00164bcb |
  # | red       | #dc322f | ESC[1;31m | red       | LightRed    | Red         | 12         | 002f32dc |
  # | magenta   | #d33682 | ESC[1;35m | magenta   | LightPurple | Magenta     | 13         | 008236d3 |
  # | violet    | #6c71c4 | ESC[0;35m | brmagenta | Purple      | DarkMagenta | 05         | 00c4716c |
  # | blue      | #268bd2 | ESC[1;34m | blue      | LightBlue   | Blue        | 09         | 00d28b26 |
  # | cyan      | #2aa198 | ESC[1;36m | cyan      | LightAqua   | Cyan        | 11         | 0098a12a |
  # | green     | #859900 | ESC[1;32m | green     | LightGreen  | Green       | 10         | 00009985 |
  

  PS1="\[$(tput setaf 0) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 1) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 2) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 3) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 4) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 5) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 6) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 7) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 8) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 9) \]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 10)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 11)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 12)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 13)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 14)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 15)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 16)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 17)\]my prompt\[$(tput sgr0)\]> "
  PS1="\[$(tput setaf 18)\]my prompt\[$(tput sgr0)\]> "
  

  

  • or ps1 with conditions

    $ DEFAULT="\[$(tput setaf 3)\]"         # or '\[\033[1;38;5;3m\]'     or '\[\e[1;33m\]'
    $ ifDEFAULT='\[\e[1\;33m\]'             # or '\[\033[1\;38\;5\;3m\]'
    $ ifRED='\[\e[1\;31m\]'                 # or '\[\033[1\;38\;5\;1m\]'
    $ PS1="${DEFAULT}my prompt${RESET} \$( if [ \$? != 0 ]; then echo -e ${ifRED}\\$; else echo -e ${ifDEFAULT}\\$; fi) ${RESET}"
    

    

functions

function showKeyMap() { RET=$?; bind -v | awk '/keymap/ {print $NF}'; return "${RET}"; }
function rightPrompt() {
  if [ "$(bind -v | awk '/keymap/ {print $NF}')" == 'emacs' ]; then
    kmap=⌁
  else
    kmap=⚙︎
  fi
  printf "%*s" $COLUMNS "${kmap}"
}

PS1+="- [\$(showKeyMap)] "
PS1+="- [\$(tput sc; rightPrompt; tput rc)]"

• right prompt

  rightprompt() { printf "%*s" $COLUMNS "right prompt"; }
  PS1='\[$(tput sc; rightprompt; tput rc)\]left prompt > '
  

  

character

metacharacter

process substitution

[!TIP] Process substitution is a form of redirection where the input or output of a process (some sequence of commands) appear as a temporary file. reference:

• chapter 23. process substitution Command list enclosed within parentheses

  >(command_list)
  <(command_list)
  

  Process substitution uses /dev/fd/<n> files to send the results of the process(es) within parentheses to another process. [1]

$ while read branch; do
    git fetch --all --force;
  done < <(git rev-parse --abbrev-ref HEAD)

$ echo >(true)
/dev/fd/63
$ echo <(true)
/dev/fd/63

$ echo >(true) <(true)
/dev/fd/63 /dev/fd/62

$ echo <(date)
/dev/fd/63
$ cat <(date)
Tue Dec 15 22:32:08 CST 2020

named pipe similar

$ wc <(cat /usr/share/dict/words)
 235886  235886 2493109 /dev/fd/63
$ cat /usr/share/dict/words | wc
 235886  235886 249310

$ wc <(grep script /usr/share/dict/words)
    176     176    5414 /dev/fd/63
$ grep script /usr/share/dict/words | wc
    176     176    5414

# https://superuser.com/a/1059790/112396
$ cat file | while read line; do ((count++)); done
$ while read line; do ((count++)); done < <(cat file)

get diff in two folders

$ diff <(ls ibook) <(ls mbook)
1c1,2
< book.json
---
> _book
> book.json
3a5
> node_modules

$ diff <(sleep 4; date) <(sleep 5; date)
1c1
< Tue Dec 15 22:48:31 CST 2020
---
> Tue Dec 15 22:48:32 CST 2020

example: run script without download

$ bash < <(wget -qO - https://raw.githubusercontent.com/ubports/unity8-desktop-install-tools/master/install.sh)

• via curl

  $ python < <(curl -s https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/meminfo.py)
  

  • or

    $ curl -so - https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/meminfo.py | python
    

• via wget

  $ python < <(wget -O - -q -t 1 https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/meminfo.py)
  

  • or

    $ wget -qO - https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/meminfo.py | python
    

• or

  $ python < <(curl -s https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/meminfo.py)
  MEMORY
  ------
  Total      :   16.0G
  Available  :    5.8G
  Percent    :    63.8
  Used       :    8.8G
  Free       :  204.5M
  Active     :    5.4G
  Inactive   :    5.6G
  Wired      :    3.4G
  
  SWAP
  ----
  Total      :    1.0G
  Used       :  269.2M
  Free       :  754.8M
  Percent    :    26.3
  Sin        :   38.3G
  Sout       :   63.9M
  

• or

  $ python < <(curl -s https://raw.githubusercontent.com/giampaolo/psutil/master/scripts/disk_usage.py)
  Device               Total     Used     Free  Use %      Type  Mount
  /dev/disk1s5        233.5G    10.6G    70.6G    13%      apfs  /
  /dev/disk1s1        233.5G   149.6G    70.6G    67%      apfs  /System/Volumes/Data
  /dev/disk1s4        233.5G     2.0G    70.6G     2%      apfs  /private/var/vm
  /Library/Input Methods/SogouInput.app   233.5G   149.1G    71.1G    67%    nullfs  /private/var/folders/s3/mg_f3cv54nn7y758j_t46zt40000gn/T/AppTranslocation/E29031DE-FE63-4ABC-BA3D-E99C743E57D2
  

example: merge lines of file

inspired by here and here

$ cat a
t1
t2
t3
t4
$ cat b
11
22
33
44

$ paste <(cat a) <(cat b)
t1  11
t2  22
t3  33
t4  44

• additional usage

  $ cat a | paste -d'\t' - - - -
  a b c d
  e f
  

  or

  $ cat a | paste -d, - -
  a,b
  c,d
  e,f
  

• /dev/fd/63 is not a regular file

  $ more <( ls -l )
  /dev/fd/63 is not a regular file (use -f to see it)
  
  $ more -f <( ls -l )
  total 12
  -rw-r--r--  1 marslo staff 3457 Nov  2 15:53 README.md
  -rw-r--r--  1 marslo staff 4314 Nov  2 15:53 SUMMARY.md
  drwxr-xr-x  6 marslo staff  192 Oct 12 22:10 artifactory
  drwxr-xr-x  8 marslo staff  256 Sep 29 17:40 cheatsheet
  drwxr-xr-x 12 marslo staff  384 Oct 15 15:27 devops
  drwxr-xr-x  7 marslo staff  224 Sep 28 22:17 jenkins
  drwxr-xr-x 11 marslo staff  352 Sep 28 22:17 kubernetes
  drwxr-xr-x  8 marslo staff  256 Oct  9 19:15 linux
  drwxr-xr-x  8 marslo staff  256 Nov  2 15:51 osx
  drwxr-xr-x  6 marslo staff  192 Sep 28 22:17 programming
  drwxr-xr-x 45 marslo staff 1440 Nov  2 13:56 screenshot
  drwxr-xr-x 11 marslo staff  352 Oct 14 21:22 tools
  

nstalling tools via running random scripts from unknown sites

$ ( wget -O - pi.dk/3 || lynx -source pi.dk/3 || curl pi.dk/3/ || \
    fetch -o - http://pi.dk/3 ) > install.sh

strace

[!NOTE|label:reference]

• What's the difference between <<, <<< and < < in bash?

basic commands

du

• top biggest directories under [path]

  $ du -a [path] | sort -n -r | head -n 5
  

• display the largest files according to human-readable format

  $ du -hs * | sort -rh | head -5
  

• display the largest folders/files including the sub-directories

  $ du -Sh | sort -rh | head -5
  

• biggest file sizes

  $ find -type f -exec du -Sh {} + | sort -rh | head -n 5
  
  # or
  $ find [PATH] -type f -printf "%s %p\n" | sort -rn | head -n 5
  

sort

sort result via human-readable format

$ sudo du -ahx --max-depth=1 <path> | sort -k1 -rh

• or

  $ du -sk * | sort -g | awk '{
  
      numBytes = $1 * 1024;
      numUnits = split("B K M G T P", unit);
      num = numBytes;
      iUnit = 0;
  
      while(num >= 1024 && iUnit + 1 < numUnits) {
          num = num / 1024;
          iUnit++;
      }
  
      $1 = sprintf( ((num == 0) ? "%6d%s " : "%6.1f%s "), num, unit[iUnit + 1]);
      print $0;
  
  }'
  
  # or in one-line
  $ du -sk * | sort -g | awk '{ numBytes = $1 * 1024; numUnits = split("B K M G T P", unit); num = numBytes; iUnit = 0; while(num >= 1024 && iUnit + 1 < numUnits) { num = num / 1024; iUnit++; } $1 = sprintf( ((num == 0) ? "%6d%s " : "%6.1f%s "), num, unit[iUnit + 1]); print $0; }'
  

• or

  #! /usr/bin/env bash
  ducks () {
      du -cks -x | sort -n | while read size fname; do
          for unit in k M G T P E Z Y; do
              if [ $size -lt 1024 ]; then
                  echo -e "${size}${unit}\t${fname}"
                  break
              fi
              size=$((size/1024))
          done
      done
  }
  ducks > .ducks && tail .ducks
  

• or

  $ du -k ./* |
       sort -nr |
       awk '{ split("KB,MB,GB",size,","); }
            { x = 1;while ($1 >= 1024) {$1 = $1 / 1024;x = x + 1} $1 = sprintf("%-4.2f%s", $1, size[x]); print $0; }'
  

others

you have new mail

• remove

  $ mail
  ? delete *
  No applicable messages.
  ? q
  

  • or

    $ mail -N
    ? d *
    ? quit
    

crontab

[!NOTE|label:references:]

• Linux / UNIX Crontab File Location
• * cron.help
  • Cron Examples
• Cron Jobs: The Complete Guide for 2023

• format

  *    *    *    *    *   /home/user/bin/somecommand.sh
  |    |    |    |    |            |
  |    |    |    |    |    Command or Script to execute
  |    |    |    |    |
  |    |    |    | Day of week(0-6 | Sun-Sat)
  |    |    |    |
  |    |    |  Month(1-12)
  |    |    |
  |    |  Day of Month(1-31)
  |    |
  |   Hour(0-23)
  |
  Min(0-59)
  

• tips

  • every odd hours

    0 1-23/2 * * *
    

  • every even hours

    0 */2 * * *
    

• sample

  • delete .DS_

    15 */2 * * 1-5 /usr/local/bin/fd --type f --hidden --follow --unrestricted --color=never --exclude .Trash --glob '*\.DS_*' $HOME | xargs -r rm
    # or
    30 */2 * * 1-5 /usr/local/bin/fd -Iu --glob '*\.DS_*' $HOME | xargs -r rm
    # or
    30 */2 * * 1-5 /usr/local/bin/rg --hidden --smart-case --color=never --files "$HOME" -g '*\.DS_*' | xargs -r rm
    

  • flush disk cache

    0 * * * * /usr/sbin/purge
    

  • flush DNS

    0 1-23/6 * * * /usr/bin/killall -HUP mDNSResponder
    

• localtion

  • macos

    $ sudo ls -Altrh /usr/lib/cron/tabs/<USERNAME>
    

  • freebsd/openbsd/netbsd

    $ sudo ls -Altrh /var/cron/tabs/<USERNAME>
    

  • centos/rhel/fedora/scientific/rocky/alma linux

    $ sudo ls -Altrh /var/spool/cron/<USERNAME>
    

  • debian/ubuntu/mint linux

    $ sudo ls -Altrh /var/spool/cron/crontabs/<USERNAME>
    

  • p-ux unix

    $ sudo ls -Altrh /var/spool/cron/crontabs/<USERNAME>
    

  • ibm aix unix

    $ sudo ls -Altrh /var/spool/cron/<USERNAME>
    

tricky

unicode

$ echo $'\xc3a9'
a9

$ echo $'\xe2\x98\xa0'
☠
$ echo $'(U+2620) \U02620' | xxd
00000000: 2855 2b32 3632 3029 20e2 98a0 0a         (U+2620) ....

# test
for (( i=0x2500; i<0x2600; i++ )); do
    UnicodePointToUtf8 $i
    [ "$(( i+1 & 0x1f ))" != 0 ] || echo ""
done
─━│┃┄┅┆┇┈┉┊┋┌┍┎┏┐┑┒┓└┕┖┗┘┙┚┛├┝┞┟
┠┡┢┣┤┥┦┧┨┩┪┫┬┭┮┯┰┱┲┳┴┵┶┷┸┹┺┻┼┽┾┿
╀╁╂╃╄╅╆╇╈╉╊╋╌╍╎╏═║╒╓╔╕╖╗╘╙╚╛╜╝╞╟
╠╡╢╣╤╥╦╧╨╩╪╫╬╭╮╯╰╱╲╳╴╵╶╷╸╹╺╻╼╽╾╿
▀▁▂▃▄▅▆▇█▉▊▋▌▍▎▏▐░▒▓▔▕▖▗▘▙▚▛▜▝▞▟
■□▢▣▤▥▦▧▨▩▪▫▬▭▮▯▰▱▲△▴▵▶▷▸▹►▻▼▽▾▿
◀◁◂◃◄◅◆◇◈◉◊○◌◍◎●◐◑◒◓◔◕◖◗◘◙◚◛◜◝◞◟
◠◡◢◣◤◥◦◧◨◩◪◫◬◭◮◯◰◱◲◳◴◵◶◷◸◹◺◻◼◽◾◿

## test harness
for (( i=0x2500; i<0x2600; i++ )); do
    unichr $i
done
─━│┃┄┅┆┇┈┉┊┋┌┍┎┏┐┑┒┓└┕┖┗┘┙┚┛├┝┞┟┠┡┢┣┤┥┦┧┨┩┪┫┬┭┮┯┰┱┲┳┴┵┶┷┸┹┺┻┼┽┾┿╀╁╂╃╄╅╆╇╈╉╊╋╌╍╎╏═║╒╓╔╕╖╗╘╙╚╛╜╝╞╟╠╡╢╣╤╥╦╧╨╩╪╫╬╭╮╯╰╱╲╳╴╵╶╷╸╹╺╻╼╽╾╿▀▁▂▃▄▅▆▇█▉▊▋▌▍▎▏▐░▒▓▔▕▖▗▘▙▚▛▜▝▞▟■□▢▣▤▥▦▧▨▩▪▫▬▭▮▯▰▱▲△▴▵▶▷▸▹►▻▼▽▾▿◀◁◂◃◄◅◆◇◈◉◊○◌◍◎●◐◑◒◓◔◕◖◗◘◙◚◛◜◝◞◟◠◡◢◣◤◥◦◧◨◩◪◫◬◭◮◯◰◱◲◳◴◵◶◷◸◹◺◻◼◽◾◿

# https://stackoverflow.com/a/55639328/2940319
$ echo -e "\U1F304"
�
$ echo -e "�" | hexdump -C
00000000  f0 9f 8c 84 0a                                    |.....|
00000005

• unicode to utf8

  UnicodePointToUtf8()
  {
      local x="$1"               # ok if '0x2620'
      x=${x/\\u/0x}              # '\u2620' -> '0x2620'
      x=${x/U+/0x}; x=${x/u+/0x} # 'U-2620' -> '0x2620'
      x=$((x)) # from hex to decimal
      local y=$x n=0
      [ $x -ge 0 ] || return 1
      while [ $y -gt 0 ]; do y=$((y>>1)); n=$((n+1)); done
      if [ $n -le 7 ]; then       # 7
          y=$x
      elif [ $n -le 11 ]; then    # 5+6
          y=" $(( ((x>> 6)&0x1F)+0xC0 )) \
              $(( (x&0x3F)+0x80 ))"
      elif [ $n -le 16 ]; then    # 4+6+6
          y=" $(( ((x>>12)&0x0F)+0xE0 )) \
              $(( ((x>> 6)&0x3F)+0x80 )) \
              $(( (x&0x3F)+0x80 ))"
      else                        # 3+6+6+6
          y=" $(( ((x>>18)&0x07)+0xF0 )) \
              $(( ((x>>12)&0x3F)+0x80 )) \
              $(( ((x>> 6)&0x3F)+0x80 )) \
              $(( (x&0x3F)+0x80 ))"
      fi
      printf -v y '\\x%x' $y
      echo -n -e $y
  }
  

• unichr

  fast_chr() {
      local __octal
      local __char
      printf -v __octal '%03o' $1
      printf -v __char \\$__octal
      REPLY=$__char
  }
  
  function unichr {
      local c=$1  # Ordinal of char
      local l=0   # Byte ctr
      local o=63  # Ceiling
      local p=128 # Accum. bits
      local s=''  # Output string
  
      (( c < 0x80 )) && { fast_chr "$c"; echo -n "$REPLY"; return; }
  
      while (( c > o )); do
          fast_chr $(( t = 0x80 | c & 0x3f ))
          s="$REPLY$s"
          (( c >>= 6, l++, p += o+1, o>>=1 ))
      done
  
      fast_chr $(( t = p | c ))
      echo -n "$REPLY$s"
  }
  

useful functions

• universal extract

  function extract () {
    case $1 in
      *.tar.bz2) tar xjf "$1" ;;
      *.tar.gz) tar xzf "$1" ;;
      *.tar.xz) tar Jxvf "$1" ;;
      *.tar.Z) tar xzf "$1" ;;
      *.tar) tar xf "$1" ;;
      *.taz) tar xzf "$1" ;;
      *.tb2) tar xjf "$1" ;;
      *.tbz) tar xjf "$1" ;;
      *.tbz2) tar xjf "$1" ;;
      *.tgz) tar xzf "$1" ;;
      *.txz) tar Jxvf "$1" ;;
      *.zip) unzip "$1" ;;
      *.gz) gunzip "$1" ;;
      *) echo "'$1' cannot be extracted" ;;
    esac
  }
  

  search manual page

• whatis -r <string>
• apropos -r <string>