This shell script prepares package.xml file and downloads metadata in source format.

DownloadMetadataInSourceFormat.sh

#!/bin/bash

prepare_wildcard_package (){
    echo "  <types>" >> package_temp.xml
    echo "    <members>*</members>" >> package_temp.xml
    echo "    <name>$1</name>" >> package_temp.xml
    echo "  </types>" >> package_temp.xml
}

rm -f temp.txt
rm -f package_temp.xml
echo "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>\n" >> package_temp.xml
echo "<Package xmlns=\"http://soap.sforce.com/2006/04/metadata\">" >> package_temp.xml

sfdx force:mdapi:listmetadata --metadatatype=EmailFolder --targetusername=$1 --json | jq '.result[].fullName' > temp.txt
input="temp.txt"
echo "  <types>" >> package_temp.xml
while IFS= read -r line
do
    folderName="${line//\"/}" 
    #folderName="'$id'"
    echo "$folderName"
    rm -f temp_1.txt
    sfdx force:mdapi:listmetadata --metadatatype=EmailTemplate --folder=$folderName --targetusername=$1 --json | jq '.result[].fullName' >> temp_1.txt
    while IFS= read -r line1
    do
        templateName="${line1//\"/}"
        echo "    <members>$templateName</members>" >> package_temp.xml
    done < "temp_1.txt"
    rm -f temp_1.txt
done < "$input"
echo "    <name>EmailTemplate</name>" >> package_temp.xml
echo "  </types>" >> package_temp.xml
rm -f temp.txt

# this below section prepares package.xml for CustomObject type.
echo "  <types>" >> package_temp.xml
sfdx force:mdapi:listmetadata --metadatatype=CustomObject --targetusername=$1 --json | jq '.result[].fullName' > temp.txt
input="temp.txt"
while IFS= read -r line
do
  objName="${line//\"/}"
  echo "    <members>$objName</members>" >> package_temp.xml
done < "$input"
echo "    <name>CustomObject</name>" >> package_temp.xml
echo "  </types>" >> package_temp.xml
rm -f temp.txt


#this below section prepares package.xml for Layout.
echo "  <types>" >> package_temp.xml
sfdx force:mdapi:listmetadata --metadatatype=Layout --targetusername=$1 --json | jq '.result[]' | jq '"\(.fullName)____\(.manageableState)____\(.namespacePrefix)"' > temp.txt
input="temp.txt"
while IFS= read -r line
do
    line="${line//\"/}"
    layoutType=$(awk -F'____' '{print $2}' <<< $line) # this gives whether it is installed or unmanaged
    if [ $layoutType == "installed" ] 
    then
        fullLayoutName=$(awk -F'____' '{print $1}' <<< $line)
        objName=$(awk -F'-' '{print $1}' <<< $fullLayoutName)
        layOutName=$(awk -F'-' '{print $2}' <<< $fullLayoutName)
        nameSpacePrefix=$(awk -F'____' '{print $3}' <<< $line)
        fixedLayoutName=$objName-$nameSpacePrefix"__"$layOutName
        echo "    <members>$fixedLayoutName</members>" >> package_temp.xml
    else
        fullLayoutName=$(awk -F'____' '{print $1}' <<< $line)
        echo "    <members>$fullLayoutName</members>" >> package_temp.xml
    fi
done < "$input"
echo "    <name>Layout</name>" >> package_temp.xml
echo "  </types>" >> package_temp.xml
rm -f temp.txt


prepare_wildcard_package ApexClass
prepare_wildcard_package ApexTrigger
prepare_wildcard_package ApexComponent
prepare_wildcard_package ApexPage
prepare_wildcard_package AuraDefinitionBundle
prepare_wildcard_package LightningComponentBundle
prepare_wildcard_package Flow
prepare_wildcard_package CustomMetadata


echo "  <version>46.0</version>" >> package_temp.xml
echo "</Package>" >> package_temp.xml
cat package_temp.xml

sfdx force:source:retrieve --targetusername=$1 --manifest=package_temp.xml 

rm -f force-app/main/default/flows/dat_case_closure_survey.flow-meta.xml
rm -f force-app/main/default/objects/Survey/listViews/My\ Surveys.listView-meta.xml