Get all users from the sharepoint group

public static string GetAllGroupUsers(string GroupName)
        {
            string userList = string.Empty;

            SPSite spSite = new SPSite(SPContext.Current.Site.ID);
            using (SPWeb spWeb = spSite.RootWeb)
            {
                try
                {
                    SPGroup spGroup = spWeb.SiteGroups[GroupName];
                    if (spGroup != null)
                    {
                        foreach (SPUser spUser in spGroup.Users)
                        {
                            userList += spUser.Email + ";";
                        }
                    }
                }
                catch (Exception ex)
                {
                   
                }
            }
            return userList;
        }

Copy Users from One SharePoint Group to Another using PowerShell

Recently, I had a requirement to copy users from one SharePoint group to another group. Unfortunately, SharePoint doesn't support nested groups. Simply renaming the group didn't help us! Well, There is no direct way to copy users from one group to another, but without having to retype each user IDs, you can use this trick to save time in copy-move SharePoint users: 

• Go to Site Actions >> Site Settings
• Click on "People and Groups" under Users and Permissions group
• Pick required users from the source group. Click on "E-mail Users" from "Actions" menu.
  
• This launches the default E-mail client such as Outlook. Now you can copy those IDs.
• Head-on to the Target SharePoint group >> Add users and paste those copied IDs.

The above method could be relatively simpler when you have to copy or move few users between SharePoint groups. Wouldn't it be better to use the scripted way to copy multiple users in bulk?

PowerShell Script to Copy/Move Users from One SharePoint Group to Another :

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Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue   #Input variables $WebURL = "http://sharepoint.crescent.com/sites/Operations/" $SourceGroupName="Operations Members" $TargetGroupName="Operations Owners"   #Get the Web $web = Get-SPWeb $WebURL   #Get the Source and Target Groups $SourceGroup = $web.groups | where {$_.name -eq $SourceGroupName } $TargetGroup = $web.groups | where {$_.name -eq $TargetGroupName }   #Iterate through each users in the source group foreach ($user in $SourceGroup.users) {    $TargetGroup.AddUser($user)     Write-Host "Copied $user from $SourceGroup to $TargetGroup"     #To move users, Just remove them from source group     #$SourceGroup.RemoveUser($user) }

Copy users from one SharePoint site collection to another using PowerShell:
The above script copies users between SharePoint groups of the same site. Can we copy users between groups in different site collections? Why not? Lets change the above script slightly to copy users from one SharePoint site group to another.

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Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue   #Input variables $SourceWebURL = "http://sharepoint.crescent.com/sites/Operations/" $TargetWebURL = "http://sharepoint.crescent.com/sites/Marketing/" $SourceGroupName="Operations Members" $TargetGroupName="Marketing Members"   #Get the Webs $SourceWeb = Get-SPWeb $SourceWebURL $TargetWebURL= Get-SPWeb $TargetWebURL   #Get the Source and Target Groups $SourceGroup = $SourceWeb.groups | where {$_.name -eq $SourceGroupName } $TargetGroup = $TargetWebURL.groups | where {$_.name -eq $TargetGroupName }   #Iterate through each users in the source group foreach ($user in $SourceGroup.users) {    $TargetGroup.AddUser($user)     Write-Host "Copied $user from $SourceGroup to $TargetGroup"     #To move users, Just remove them from source group     #$SourceGroup.RemoveUser($user) }

Reference:
http://www.sharepointdiary.com/2014/04/copy-users-from-one-sharepoint-group-to-another-using-powershell.html