Access Safari Bookmarks in Macos Mojave Programmatically

Access safari bookmarks in macOS Mojave programmatically

You cannot access ~/Library/Safari/Bookmarks.plist anymore because of the stricter security rules in Mojave.

I don't think there's an API to do this specific action yet, so the solution for now is to add the application yourself to System Preferences > Security > Confidentiality > Disk access.

For example if you add Terminal.app to this Confidentiality subgroup, this will grant access to the whole disk to all commands executed in Terminal, inluding using cat/vim/... to access ~/Library/Safari/Bookmarks.plist.

How to create and manage macOS Safari bookmarks programmatically?

tl;dr It's necessary to edit Safari's Bookmarks.plist to create bookmarks programmatically. Checkout the "Using a Python script" section below. It entails utilizing a XSLT stylesheet in a Bash script and invoking it via your .py file. All tooling required to achieve this are builtin on macOS.

Important: Using macOS Mojave (10.14.x)+ you need to perform steps 1-10 in the "MacOS Mojave Restrictions" section below. Those changes permit modifications to Bookmarks.plist.

Before proceeding create a copy of Bookmarks.plist which can be found at ~/Library/Safari/Bookmarks.plist. You can run the following command to copy it to your Desktop:

cp ~/Library/Safari/Bookmarks.plist ~/Desktop/Bookmarks.plist

To restore Bookmarks.plist later run:

cp ~/Desktop/Bookmarks.plist ~/Library/Safari/Bookmarks.plist

Property Lists

MacOS has builtin Property List (.plist) related command line tools, namely plutil, and defaults, which lend themselves to editing application preferences that typically contain flat data structures. However Safari's Bookmarks.plist has a deeply nested structure, which neither of these tools are good at editing.

Tranforming .plist files to XML

plutil provides a -convert option to transform .plist from binary to XML. For instance:

plutil -convert xml1 ~/Library/Safari/Bookmarks.plist

Similarily, the following command transforms to binary:

plutil -convert binary1 ~/Library/Safari/Bookmarks.plist

Converting to XML enables use of XSLT which is ideal for transforming complex XML structures.

Using a XSLT Stylesheet

This custom XSLT stylesheet transforms Bookmarks.plist adding element nodes to create bookmarks:

template.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:strip-space elements="*"/>
  <xsl:output
    method="xml"
    indent="yes"
    doctype-system="http://www.apple.com/DTDs/PropertyList-1.0.dtd"
    doctype-public="-//Apple//DTD PLIST 1.0//EN"/>

  <xsl:param name="bkmarks-folder"/>
  <xsl:param name="bkmarks"/>
  <xsl:param name="guid"/>
  <xsl:param name="keep-existing" select="false" />

  <xsl:variable name="bmCount">
    <xsl:value-of select="string-length($bkmarks) -
          string-length(translate($bkmarks, ',', '')) + 1"/>
  </xsl:variable>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()" />
    </xsl:copy>
  </xsl:template>

  <xsl:template name="getNthValue">
    <xsl:param name="list"/>
    <xsl:param name="n"/>
    <xsl:param name="delimiter"/>

    <xsl:choose>
      <xsl:when test="$n = 1">
        <xsl:value-of select=
              "substring-before(concat($list, $delimiter), $delimiter)"/>
      </xsl:when>
      <xsl:when test="contains($list, $delimiter) and $n > 1">
        <!-- recursive call -->
        <xsl:call-template name="getNthValue">
          <xsl:with-param name="list"
              select="substring-after($list, $delimiter)"/>
          <xsl:with-param name="n" select="$n - 1"/>
          <xsl:with-param name="delimiter" select="$delimiter"/>
        </xsl:call-template>
      </xsl:when>
    </xsl:choose>
  </xsl:template>

  <xsl:template name="createBmEntryFragment">
    <xsl:param name="loopCount" select="1"/>

    <xsl:variable name="bmInfo">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bkmarks"/>
        <xsl:with-param name="delimiter" select="','"/>
        <xsl:with-param name="n" select="$loopCount"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmkName">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="1"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmURL">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="2"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmGUID">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="3"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:if test="$loopCount > 0">
      <dict>
        <key>ReadingListNonSync</key>
        <dict>
          <key>neverFetchMetadata</key>
          <false/>
        </dict>
        <key>URIDictionary</key>
        <dict>
          <key>title</key>
          <string>
            <xsl:value-of select="$bmkName"/>
          </string>
        </dict>
        <key>URLString</key>
        <string>
          <xsl:value-of select="$bmURL"/>
        </string>
        <key>WebBookmarkType</key>
        <string>WebBookmarkTypeLeaf</string>
        <key>WebBookmarkUUID</key>
        <string>
          <xsl:value-of select="$bmGUID"/>
        </string>
      </dict>
      <!-- recursive call -->
      <xsl:call-template name="createBmEntryFragment">
        <xsl:with-param name="loopCount" select="$loopCount - 1"/>
      </xsl:call-template>
    </xsl:if>
  </xsl:template>

  <xsl:template name="createBmFolderFragment">
    <dict>
      <key>Children</key>
      <array>
        <xsl:call-template name="createBmEntryFragment">
          <xsl:with-param name="loopCount" select="$bmCount"/>
        </xsl:call-template>
        <xsl:if test="$keep-existing = 'true'">
          <xsl:copy-of select="./array/node()|@*"/>
        </xsl:if>
      </array>
      <key>Title</key>
      <string>
        <xsl:value-of select="$bkmarks-folder"/>
      </string>
      <key>WebBookmarkType</key>
      <string>WebBookmarkTypeList</string>
      <key>WebBookmarkUUID</key>
      <string>
        <xsl:value-of select="$guid"/>
      </string>
    </dict>
  </xsl:template>

  <xsl:template match="dict[string[text()='BookmarksBar']]/array">
    <array>
      <xsl:for-each select="dict">
        <xsl:choose>
          <xsl:when test="string[text()=$bkmarks-folder]">
            <xsl:call-template name="createBmFolderFragment"/>
          </xsl:when>
          <xsl:otherwise>
            <xsl:copy>
              <xsl:apply-templates select="@*|node()" />
            </xsl:copy>
          </xsl:otherwise>
        </xsl:choose>
      </xsl:for-each>

      <xsl:if test="not(./dict/string[text()=$bkmarks-folder])">
        <xsl:call-template name="createBmFolderFragment"/>
      </xsl:if>
    </array>
  </xsl:template>

</xsl:stylesheet>

Running a transformation:

This .xsl requires parameters that specify the properties of each required bookmark.

Firstly ensure that Bookmarks.plits is XML formatted:

plutil -convert xml1 ~/Library/Safari/Bookmarks.plist

Utilize the builtin xsltproc to apply template.xsl to Bookmarks.plist.

Firstly, cd to where template.xsl resides, and run this compound command:

guid1=$(uuidgen) && guid2=$(uuidgen) && guid3=$(uuidgen) && xsltproc --novalid --stringparam bkmarks-folder "QUUX" --stringparam bkmarks "r/Android https://www.reddit.com/r/Android/ ${guid1},r/Apple https://www.reddit.com/r/Apple/ ${guid2}" --stringparam guid "$guid3" ./template.xsl - <~/Library/Safari/Bookmarks.plist > ~/Desktop/result-plist.xml

This creates result-plist.xml on your Desktop containing a new bookmarks folder named QUUX with two new bookmarks.

Let's further understand each part in the aforementioned compound command:
- uuidgen generates three UUID's that are required in the new Bookmarks.plist (one for the folder, and one for each bookmark entry). We generate them upfront and pass them to the XSLT because:
  - XSLT 1.0 doesn't have a feature for UUID generation.
  - xsltproc requires XSLT 1.0
- xsltproc's --stringparam option denotes custom arguments as follows:
  - --stringparam bkmarks-folder <value> - Name of the bookmark folder.
  - --stringparam bkmarks <value> - Properties for each bookmark.
    Each bookmark spec is delimited with a comma (,). Each delimited string has three values; the name of bookmark, the URL, and GUID. These 3 values are space delimited.
  - --stringparam guid <value> - GUID for the bookmark folder.
- The last parts:
```
./template.xsl - <~/Library/Safari/Bookmarks.plist > ~/Desktop/result-plist.xml
```
  define paths to; the .xsl, source XML, and destination.
To evaluate the transformation that just occurred utilize diff to display differences between the two files. For instance run:
```
diff -yb --width 200 ~/Library/Safari/Bookmarks.plist ~/Desktop/result-plist.xml | less
```
Then press the F key several times to navigate forward to each page until you see > symbols in the middle of the two columns - they indicate where new element nodes have been addede. Press the B key to move back a page, and type Q to exit diff.

Using a Bash script.

We can now utilize the aforementioned .xsl in a Bash script.

script.sh

#!/usr/bin/env bash

declare -r plist_path=~/Library/Safari/Bookmarks.plist

# ANSI/VT100 Control sequences for colored error log.
declare -r fmt_red='\x1b[31m'
declare -r fmt_norm='\x1b[0m'
declare -r fmt_green='\x1b[32m'
declare -r fmt_bg_black='\x1b[40m'

declare -r error_badge="${fmt_red}${fmt_bg_black}ERR!${fmt_norm}"
declare -r tick_symbol="${fmt_green}\\xE2\\x9C\\x94${fmt_norm}"

if [ -z "$1" ] || [ -z "$2" ]; then
  echo -e "${error_badge} Missing required arguments" >&2
  exit 1
fi

bkmarks_folder_name=$1
bkmarks_spec=$2

keep_existing_bkmarks=${3:-false}

# Transform bookmark spec string into array using comma `,` as delimiter.
IFS=',' read -r -a bkmarks_spec <<< "${bkmarks_spec//, /,}"

# Append UUID/GUID to each bookmark spec element.
bkmarks_spec_with_uuid=()
while read -rd ''; do
  [[ $REPLY ]] && bkmarks_spec_with_uuid+=("${REPLY} $(uuidgen)")
done < <(printf '%s\0' "${bkmarks_spec[@]}")

# Transform bookmark spec array back to string using comma `,` as delimiter.
bkmarks_spec_str=$(printf '%s,' "${bkmarks_spec_with_uuid[@]}")
bkmarks_spec_str=${bkmarks_spec_str%,} # Omit trailing comma character.

# Check the .plist file exists.
if [ ! -f "$plist_path" ]; then
  echo -e "${error_badge} File not found: ${plist_path}" >&2
  exit 1
fi

# Verify that plist exists and contains no syntax errors.
if ! plutil -lint -s "$plist_path" >/dev/null; then
  echo -e "${error_badge} Broken or missing plist: ${plist_path}" >&2
  exit 1
fi

# Ignore ShellCheck errors regarding XSLT variable references in template below.
# shellcheck disable=SC2154
xslt() {
cat <<'EOX'
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:strip-space elements="*"/>
  <xsl:output
    method="xml"
    indent="yes"
    doctype-system="http://www.apple.com/DTDs/PropertyList-1.0.dtd"
    doctype-public="-//Apple//DTD PLIST 1.0//EN"/>

  <xsl:param name="bkmarks-folder"/>
  <xsl:param name="bkmarks"/>
  <xsl:param name="guid"/>
  <xsl:param name="keep-existing" select="false" />

  <xsl:variable name="bmCount">
    <xsl:value-of select="string-length($bkmarks) -
          string-length(translate($bkmarks, ',', '')) + 1"/>
  </xsl:variable>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()" />
    </xsl:copy>
  </xsl:template>

  <xsl:template name="getNthValue">
    <xsl:param name="list"/>
    <xsl:param name="n"/>
    <xsl:param name="delimiter"/>

    <xsl:choose>
      <xsl:when test="$n = 1">
        <xsl:value-of select=
              "substring-before(concat($list, $delimiter), $delimiter)"/>
      </xsl:when>
      <xsl:when test="contains($list, $delimiter) and $n > 1">
        <!-- recursive call -->
        <xsl:call-template name="getNthValue">
          <xsl:with-param name="list"
              select="substring-after($list, $delimiter)"/>
          <xsl:with-param name="n" select="$n - 1"/>
          <xsl:with-param name="delimiter" select="$delimiter"/>
        </xsl:call-template>
      </xsl:when>
    </xsl:choose>
  </xsl:template>

  <xsl:template name="createBmEntryFragment">
    <xsl:param name="loopCount" select="1"/>

    <xsl:variable name="bmInfo">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bkmarks"/>
        <xsl:with-param name="delimiter" select="','"/>
        <xsl:with-param name="n" select="$loopCount"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmkName">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="1"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmURL">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="2"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:variable name="bmGUID">
      <xsl:call-template name="getNthValue">
        <xsl:with-param name="list" select="$bmInfo"/>
        <xsl:with-param name="delimiter" select="' '"/>
        <xsl:with-param name="n" select="3"/>
      </xsl:call-template>
    </xsl:variable>

    <xsl:if test="$loopCount > 0">
      <dict>
        <key>ReadingListNonSync</key>
        <dict>
          <key>neverFetchMetadata</key>
          <false/>
        </dict>
        <key>URIDictionary</key>
        <dict>
          <key>title</key>
          <string>
            <xsl:value-of select="$bmkName"/>
          </string>
        </dict>
        <key>URLString</key>
        <string>
          <xsl:value-of select="$bmURL"/>
        </string>
        <key>WebBookmarkType</key>
        <string>WebBookmarkTypeLeaf</string>
        <key>WebBookmarkUUID</key>
        <string>
          <xsl:value-of select="$bmGUID"/>
        </string>
      </dict>
      <!-- recursive call -->
      <xsl:call-template name="createBmEntryFragment">
        <xsl:with-param name="loopCount" select="$loopCount - 1"/>
      </xsl:call-template>
    </xsl:if>
  </xsl:template>

  <xsl:template name="createBmFolderFragment">
    <dict>
      <key>Children</key>
      <array>
        <xsl:call-template name="createBmEntryFragment">
          <xsl:with-param name="loopCount" select="$bmCount"/>
        </xsl:call-template>
        <xsl:if test="$keep-existing = 'true'">
          <xsl:copy-of select="./array/node()|@*"/>
        </xsl:if>
      </array>
      <key>Title</key>
      <string>
        <xsl:value-of select="$bkmarks-folder"/>
      </string>
      <key>WebBookmarkType</key>
      <string>WebBookmarkTypeList</string>
      <key>WebBookmarkUUID</key>
      <string>
        <xsl:value-of select="$guid"/>
      </string>
    </dict>
  </xsl:template>

  <xsl:template match="dict[string[text()='BookmarksBar']]/array">
    <array>
      <xsl:for-each select="dict">
        <xsl:choose>
          <xsl:when test="string[text()=$bkmarks-folder]">
            <xsl:call-template name="createBmFolderFragment"/>
          </xsl:when>
          <xsl:otherwise>
            <xsl:copy>
              <xsl:apply-templates select="@*|node()" />
            </xsl:copy>
          </xsl:otherwise>
        </xsl:choose>
      </xsl:for-each>

      <xsl:if test="not(./dict/string[text()=$bkmarks-folder])">
        <xsl:call-template name="createBmFolderFragment"/>
      </xsl:if>
    </array>
  </xsl:template>

</xsl:stylesheet>
EOX
}

# Convert the .plist to XML format
plutil -convert xml1 -- "$plist_path" >/dev/null || {
  echo -e "${error_badge} Cannot convert .plist to xml format" >&2
  exit 1
}

# Generate a UUID/GUID for the folder.
folder_guid=$(uuidgen)

xsltproc --novalid \
    --stringparam keep-existing "$keep_existing_bkmarks" \
    --stringparam bkmarks-folder "$bkmarks_folder_name" \
    --stringparam bkmarks "$bkmarks_spec_str" \
    --stringparam guid "$folder_guid" \
    <(xslt) - <"$plist_path" > "${TMPDIR}result-plist.xml"

# Convert the .plist to binary format
plutil -convert binary1 -- "${TMPDIR}result-plist.xml" >/dev/null || {
  echo -e "${error_badge} Cannot convert .plist to binary format" >&2
  exit 1
}

mv -- "${TMPDIR}result-plist.xml" "$plist_path" 2>/dev/null || {
  echo -e "${error_badge} Cannot move .plist from TMPDIR to ${plist_path}" >&2
  exit 1
}

echo -e "${tick_symbol} Successfully created Safari bookmarks."

Explanation

script.sh provides the following features:

Simplified API that will be beneficial when executing via Python.
Verifies the .plist is not broken.
Error handling/logging.
Transforms .plist via xsltproc using template.xsl inlined.
Creates GUID(s) for passing to XSLT based on the no. of bookmarks specified in the given arguments.
Converts .plist to XML, and back to binary.
Writes a new file to the OS's temp folder, then moves it to the Bookmarks.plist directory, effectively replacing the orginal.

Running the shell script

cd to where script.sh resides and run the following chmod command to make script.sh executable:
```
chmod +ux script.sh
```
Run the following command:
```
./script.sh "stackOverflow" "bash https://stackoverflow.com/questions/tagged/bash,python https://stackoverflow.com/questions/tagged/python"
```
The following is then printed to your CLI:

✔ Successfully created Safari bookmarks.
Safari now has a bookmarks folder named stackOverflow containing two bookmarks (bash and python).

Using a Python script

There's a couple of ways to execute script.sh via your .py file.

Method A: External shell script

The following .py file executes the external script.sh file. Let's name the file create-safari-bookmarks.py and save it in the same folder as script.sh.

create-safari-bookmarks.py

#!/usr/bin/env python

import subprocess

def run_script(folder_name, bkmarks):
    subprocess.call(["./script.sh", folder_name, bkmarks])

def tuple_to_shell_arg(tup):
    return ",".join("%s %s" % t for t in tup)

reddit_bkmarks = [
    ('r/Android', 'https://www.reddit.com/r/Android/'),
    ('r/Apple', 'https://www.reddit.com/r/Apple/'),
    ('r/Mac', 'https://www.reddit.com/r/Mac/'),
    ('r/ProgrammerHumor', 'https://www.reddit.com/r/ProgrammerHumor/'),
    ('r/gaming', 'https://www.reddit.com/r/gaming/')
]

so_bkmarks = [
    ('bash', 'https://stackoverflow.com/questions/tagged/bash'),
    ('python', 'https://stackoverflow.com/questions/tagged/python'),
    ('xslt', 'https://stackoverflow.com/questions/tagged/xslt'),
    ('xml', 'https://stackoverflow.com/questions/tagged/xml')
]

run_script('subreddit', tuple_to_shell_arg(reddit_bkmarks))
run_script("stackOverflow", tuple_to_shell_arg(so_bkmarks))

Explanation:

The first def statement defines a run-script function. It has two parameters; folder_name and bkmarks. The subprocess modules call method essentially executes script.sh with the required arguments.
The second def statement defines a tuple_to_shell_arg function. It has one parameter tup. The String join() method transforms a list of tuples into a format required by script.sh. It essentially transforms a list of tuples such as:
```
[
    ('foo', 'https://www.foo.com/'),
    ('quux', 'https://www.quux.com')
]
```
and returns a string:
```
foo https://www.foo.com/,quux https://www.quux.com
```
The run_script function is invoked as follows:
```
run_script('subreddit', tuple_to_shell_arg(reddit_bkmarks))
```
This passes two arguments; subreddit (the name of the bookmarks folder), and the spec for each required bookmark (formatted as previously described in point no. 2).

Running create-safari-bookmarks.py

Make create-safari-bookmarks.py executable:
```
chmod +ux ./create-safari-bookmarks.py
```
Then invoke it with:
```
./create-safari-bookmarks.py
```

Method B: Inline shell script

Depending on your exact use case, you may want to consider inlining script.sh in your .py file instead of calling an external .sh file. Let's name this file create-safari-bookmarks-inlined.py and save it to the same directory where create-safari-bookmarks.py resides.

Important:

You'll need to copy and paste all the content from script.sh into create-safari-bookmarks-inlined.py where indicated.
Paste it on the next line following the bash_script = """\ part.
The """ part in create-safari-bookmarks-inlined.py should be on it's own line following the last line of the pasted script.sh content.
Line 31 of script.sh when inlined in .py must have the '%s\0' part (\0 is a null character) escaped with another backslash, i.e. line 31 of script.sh should appear like this:
```
...
done < <(printf '%s\\0' "${bkmarks_spec[@]}")
                   ^
...
```
This line will probably be on line 37 in create-safari-bookmarks-inlined.py.

create-safari-bookmarks-inlined.py

#!/usr/bin/env python

import tempfile
import subprocess

bash_script = """\
# <--- Copy and paste content of `script.sh` here and modify its line 31.
"""

def run_script(script, folder_name, bkmarks):
    with tempfile.NamedTemporaryFile() as scriptfile:
        scriptfile.write(script)
        scriptfile.flush()
        subprocess.call(["/bin/bash", scriptfile.name, folder_name, bkmarks])

def tuple_to_shell_arg(tup):
    return ",".join("%s %s" % t for t in tup)

reddit_bkmarks = [
    ('r/Android', 'https://www.reddit.com/r/Android/'),
    ('r/Apple', 'https://www.reddit.com/r/Apple/'),
    ('r/Mac', 'https://www.reddit.com/r/Mac/'),
    ('r/ProgrammerHumor', 'https://www.reddit.com/r/ProgrammerHumor/'),
    ('r/gaming', 'https://www.reddit.com/r/gaming/')
]

so_bkmarks = [
    ('bash', 'https://stackoverflow.com/questions/tagged/bash'),
    ('python', 'https://stackoverflow.com/questions/tagged/python'),
    ('xslt', 'https://stackoverflow.com/questions/tagged/xslt'),
    ('xml', 'https://stackoverflow.com/questions/tagged/xml')
]

run_script(bash_script, "subreddit", tuple_to_shell_arg(reddit_bkmarks))
run_script(bash_script, "stackOverflow", tuple_to_shell_arg(so_bkmarks))

Explanation

This file achieves the same result as create-safari-bookmarks.py.
This modified .py script includes a modified run_script function that utilizes Python's tempfile module to save the inline shell script to a temporary file.
Python's subprocess modules call method then executes the temporary created shell file.

Running create-safari-bookmarks-inlined.py

Make create-safari-bookmarks-inlined.py executable:
```
chmod +ux ./create-safari-bookmarks-inlined.py
```
Then invoke it by running:
```
./create-safari-bookmarks-inlined.py
```

Additional Note: Appending bookmarks to an existing folder

Currently, each time the aforementioned scripts/commands are run again we are effectively replacing any existing named Safari bookmark folder, (which has the same name as the given bookmark folder name), with a completely new one and creating the specified bookmarks.

However, if you wanted to append bookmarks to an exiting folder then template.xsl includes one additional parameter/argument to be passed to it. Note the part on line 14 that reads:

<xsl:param name="keep-existing" select="false" />

It's default value is false. So, if we were to change the run_script function in let's say create-safari-bookmarks.py to the following.

def run_script(folder_name, bkmarks, keep_existing):
        subprocess.call(["./script.sh", folder_name, bkmarks, keep_existing])

That is to add a third parameter named keep_existing, and include a reference to it in the subprocess.call([...]), i.e. so that it gets passed as the third argument to script.sh (...and subsequently to the XSLT stylesheet).

We can then invoke the run_script function and pass in an additional String argument, either "true" or "false" like so:

run_script('subreddit', tuple_to_shell_arg(reddit_bkmarks), "true")
run_script("stackOverflow", tuple_to_shell_arg(so_bkmarks), "false")

However, making the changes above, (i.e. passing in "true" to keep existing bookmarks), does have potential to result in duplicate bookmarks being created. For example; duplicate bookmarks will occur when we have an exiting bookmark (name and URL) which is then reprovided with the same name and URL at a later time.

macOS Hight Sierra / Mojave: Programmatically get value of System Preferences - Accessibility - Display - Increase contrast

Starting on macOS 10.10 you can use this API of NSWorkspace.

Access Safari Bookmarks in Macos Mojave Programmatically