Note: `prism-shell.min.js` is actually not minimized JS file. Because I am using [MacDown](https://github.com/MacDownApp/macdown) locally, I am lazy to minimize the JS file. Just put it at `/Applications/MacDown.app/Contents/Resources/Prism/components/` and modifies your `components.js` and corresponding CSS file `my_macdown_style.css`.

components.js

...... other js codes ......

    "shell": {
      "title": "Shell",
      "owner": "sgon00" // based on zeitgeist87's bash
    },

...... other js codes ......

my_macdown_style.css

...... other css codes ......

.token.promptString {
  color: #880E4F;
}
.token.promptOthers {
  color: #222;
}
.token.cmdOut {
  font-style: italic;
  color: #999;
}

...... other css codes ......

prism-shell.min.js

(function(Prism) {
  var insideString = {
    variable: [
      // Arithmetic Environment
      {
        pattern: /\$?\(\([\w\W]+?\)\)/,
        inside: {
          // If there is a $ sign at the beginning highlight $(( and )) as variable
          variable: [{
              pattern: /(^\$\(\([\w\W]+)\)\)/,
              lookbehind: true
            },
            /^\$\(\(/,
          ],
          number: /\b-?(?:0x[\dA-Fa-f]+|\d*\.?\d+(?:[Ee]-?\d+)?)\b/,
          // Operators according to https://www.gnu.org/software/bash/manual/bashref.html#Shell-Arithmetic
          operator: /--?|-=|\+\+?|\+=|!=?|~|\*\*?|\*=|\/=?|%=?|<<=?|>>=?|<=?|>=?|==?|&&?|&=|\^=?|\|\|?|\|=|\?|:/,
          // If there is no $ sign at the beginning highlight (( and )) as punctuation
          punctuation: /\(\(?|\)\)?|,|;/
        }
      },
      // Command Substitution
      {
        pattern: /\$\([^)]+\)|`[^`]+`/,
        inside: {
          variable: /^\$\(|^`|\)$|`$/
        }
      },
      /\$(?:[a-z0-9_#\?\*!@]+|\{[^}]+\})/i
    ],
  };

  Prism.languages.shell = {
    'prompt': {
      pattern: /^[\w\d\[(@-]*((?!^)\ )?[\])~\/\w\d-]*[>%$#].*/m,
      inside: {
        'promptString': {
          pattern: /^[\w\d\[(@-]*((?!^)\ )?[\])~\/\w\d-]*[>%$#]/,
        },
        'comment': {
          pattern: /(^|[^"{\\])#.*/,
          lookbehind: true
        },
        'string': [
          //Support for Here-Documents https://en.wikipedia.org/wiki/Here_document
          {
            pattern: /((?:^|[^<])<<\s*)(?:"|')?(\w+?)(?:"|')?\s*\r?\n(?:[\s\S])*?\r?\n\2/g,
            lookbehind: true,
            inside: insideString
          },
          {
            pattern: /(["'])(?:\\\\|\\?[^\\])*?\1/g,
            inside: insideString
          }
        ],
        'variable': insideString.variable,
        // Originally based on http://ss64.com/bash/
        'function': {
          pattern: /(^|\s|;|\||&)(?:brew|flutter|alias|apropos|apt-get|aptitude|aspell|awk|basename|bash|bc|bg|builtin|bzip2|cal|cat|cd|cfdisk|chgrp|chmod|chown|chroot|chkconfig|cksum|clear|cmp|comm|command|cp|cron|crontab|csplit|cut|date|dc|dd|ddrescue|df|diff|diff3|dig|dir|dircolors|dirname|dirs|dmesg|du|egrep|eject|enable|env|ethtool|eval|exec|expand|expect|export|expr|fdformat|fdisk|fg|fgrep|file|find|fmt|fold|format|free|fsck|ftp|fuser|gawk|getopts|git|grep|groupadd|groupdel|groupmod|groups|gzip|hash|head|help|hg|history|hostname|htop|iconv|id|ifconfig|ifdown|ifup|import|install|jobs|join|kill|killall|less|link|ln|locate|logname|logout|look|lpc|lpr|lprint|lprintd|lprintq|lprm|ls|lsof|make|man|mkdir|mkfifo|mkisofs|mknod|more|most|mount|mtools|mtr|mv|mmv|nano|netstat|nice|nl|nohup|notify-send|nslookup|open|op|passwd|paste|pathchk|ping|pkill|popd|pr|printcap|printenv|printf|ps|pushd|pv|pwd|quota|quotacheck|quotactl|ram|rar|rcp|read|readarray|readonly|reboot|rename|renice|remsync|rev|rm|rmdir|rsync|screen|scp|sdiff|sed|seq|service|sftp|shift|shopt|shutdown|sleep|slocate|sort|source|split|ssh|stat|strace|su|sudo|sum|suspend|sync|tail|tar|tee|test|time|timeout|times|touch|top|traceroute|trap|tr|tsort|tty|type|ulimit|umask|umount|unalias|uname|unexpand|uniq|units|unrar|unshar|uptime|useradd|userdel|usermod|users|uuencode|uudecode|v|vdir|vi|vmstat|wait|watch|wc|wget|whereis|which|who|whoami|write|xargs|xdg-open|yes|zip)(?=$|\s|;|\||&)/,
          lookbehind: true
        },
        'keyword': {
          pattern: /(^|\s|;|\||&)(?:let|:|\.|if|then|else|elif|fi|for|break|continue|while|in|case|function|select|do|done|until|echo|exit|return|set|declare)(?=$|\s|;|\||&)/,
          lookbehind: true
        },
        'boolean': {
          pattern: /(^|\s|;|\||&)(?:true|false)(?=$|\s|;|\||&)/,
          lookbehind: true
        },
        'operator': /&&?|\|\|?|==?|!=?|<<<?|>>|<=?|>=?|=~/,
        'punctuation': /\$?\(\(?|\)\)?|\.\.|[{}[\];]/,
        'localFunction': {
          pattern: /\.\/\w+\ /,
          alias: 'function',
        },
        'promptOthers': /.*/,
      }
    },
    'comment': {
      pattern: /(^|[^"{\\])#.*/,
      lookbehind: true
    },
    'cmdOut': /\n.*/,
  };

  var inside = insideString.variable[1].inside;
  inside['function'] = Prism.languages.bash['function'];
  inside.keyword = Prism.languages.bash.keyword;
  inside.boolean = Prism.languages.bash.boolean;
  inside.operator = Prism.languages.bash.operator;
  inside.punctuation = Prism.languages.bash.punctuation;
})(Prism);

Note: prism-shell.min.js is actually not minimized JS file. Because I am using MacDown locally, I am lazy to minimize the JS file. For MacDown user, just put it at /Applications/MacDown.app/Contents/Resources/Prism/components/ and modifies your /Applications/MacDown.app/Contents/Resources/Prism/components.js and corresponding CSS file my_macdown_style.css at "/Users/<YOUR-USER-NAME>/Library/Application Support/MacDown/Styles".

@sgon00 You don't have to minify the files yourself. gulp will do that for you using the npx gulp command. It will also create components.js, so please make your changes in the .json.

On that note: The entry for bash in components.json has a shell alias which you should remove. Same for the line Prism.languages.shell = Prism.languages.bash in prism-bash.js.

As for the language itself:

1. Line 86 to 91 only work when prism-bash.js is loaded. Replacing Prism.languages.bash with Prism.languages.shell['prompt'].inside should fix that.
2. What does comment match (the one before cmdOut)? Can comments appear outside of prompt?
3. Use 'cmdOut': /.+/. That should work.

Also, when you make patterns for Prism, please be careful that they always match at least one character. Otherwise, they might cause an infinite number of zero-length matches, which causes Prism to abort at some point to prevent looping forever.