How to expand PS1?

user_96588 0
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I have a shell script that runs the same command in several directories (fgit). For each directory, I would like it to show the current prompt + the command which will be run there. How do I get the string that corresponds to the decoded (expanded)PS1? For example, my default PS1 is

${debian_chroot:+($debian_chroot)}\[\e[1;32m\]\u\[\e[0m\]@\[\e[1;32m\]\h\[\e[0m\]:\[\e[1;34m\]\w\[\e[0m\]$(__git_ps1 ' (%s)')$

and I'd like to echo the resulting prompt username@hostname:/path$, preferably (but not necessarily) with the nice colors. A cursory look at the Bash manual didn't reveal any definite answer, and echo -e $PS1 only evaluates the colors.

ps1 bash
7 Answers
  1. Expand it with ps=${ps@P} (bash 4.4)
  2. Remove between \x01 and \x02 (created by bash replacing the \[ and \] placeholder.
  3. Check all characters left
ps1_size(){
  # Ref1: https://stackoverflow.com/questions/3451993/how-to-expand-ps1
  >&2 echo -e "\nP0: Raw"
  local ps=$PS1
  echo -n "$ps" | xxd >&2 

  >&2 echo -e "\nP1: Expanding (require bash 4.4)"
  ps=${ps@P}
  echo -n "$ps" | xxd >&2 

  >&2 echo -e "\nP2: Removing everything 01 and 02"
  shopt -s extglob
  ps=${ps//$'\x01'*([^$'\x02'])$'\x02'}
  echo -n "$ps" | xxd >&2 

  >&2 echo -e "\nP3: Checking"
  if [[ "$ps" =~ [\x07\x1b\x9c] ]]; then
    # Check if escape inside
    # 07 => BEL
    # 1b => ESC
    # 9C => ST
    >&2 echo 'Warning: There is an escape code in your PS1 which is not betwwen \[ \]'
    >&2 echo "Tip: put \[ \] around your escape codes (ctlseqs + associated parameters)"
    echo -n "$ps" | xxd >&2
  # Check printable characters <= 20 .. 7e, and newline
  # -- Remove the trailing 0x0a (BEL)
  elif [[ "$ps" =~ [^[:graph:][:space:]] ]]; then
    >&2 echo 'Warning: There is a non printable character in PS1 which is not between \[ \]'
    >&2 echo "Tip: put \[ \] around your escape codes (ctlseqs + associated parameters)"
    echo "$ps"
    echo -n "$ps" | xxd >&2 
  fi

  # Echo result
  echo -n "${#ps}"
}

ps1_size

Should output something like this:

~/Software/Bash/Mouse (master)$ source ../ps1_size.sh

P0: Raw
00000000: 5c5b 5c65 5d30 3b60 7061 7273 655f 7469  \[\e]0;`parse_ti
00000010: 746c 6560 5c30 3037 5c5d 5c5b 5c65 5b33  tle`\007\]\[\e[3
00000020: 326d 5c5d 5c77 205c 5b5c 655b 3333 6d5c  2m\]\w \[\e[33m\
00000030: 5d60 7061 7273 655f 6769 745f 6272 616e  ]`parse_git_bran
00000040: 6368 605c 5b5c 655b 306d 5c5d 2420       ch`\[\e[0m\]$

P1: Expanding (require bash 4.4)
00000000: 011b 5d30 3b7e 2f53 6f66 7477 6172 652f  ..]0;~/Software/
00000010: 4261 7368 2f4d 6f75 7365 0702 011b 5b33  Bash/Mouse....[3
00000020: 326d 027e 2f53 6f66 7477 6172 652f 4261  2m.~/Software/Ba
00000030: 7368 2f4d 6f75 7365 2001 1b5b 3333 6d02  sh/Mouse ..[33m.
00000040: 286d 6173 7465 7229 011b 5b30 6d02 2420  (master)..[0m.$

P2: Removing everything 01 and 02
00000000: 7e2f 536f 6674 7761 7265 2f42 6173 682f  ~/Software/Bash/
00000010: 4d6f 7573 6520 286d 6173 7465 7229 2420  Mouse (master)$

P3: Checking
32~/Software/Bash/Mouse (master)$

If some control characters are present, you can remove it as stated in this stackoverflow: Removing ANSI color codes from text stream. I used the following to remove SCI and OSC in github: mouse_xterm.

  # Sanitize, in case
  ps=$(LC_ALL=C sed '
    # Safety
    s/\x01\|\x02//g;
    # Safety Remove OSC https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Operating-System-Commands
    # 20 .. 7e => printable characters
    # 07 => BEL
    # 9C => ST
    # 1b 5C => ESC + BS
    s/\x1b\][0-9;]*[\x20-\x7e]*\([\x07\x9C]\|\x1b\\\)//g;
    # Safety: Remove all escape sequences https://superuser.com/questions/380772/removing-ansi-color-codes-from-text-stream
    s/\x1b\[[0-9;]*[a-zA-Z]//g;
  ' <<< "$ps")
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