How to update glide list field through a script

[sam43]

How to update this glide_list field through a background script for 100 records?

[SanjivMeher]

var gr = new GlideRecord('table_name');

gr.addQuery('<add query to update the number of records you want to update>');

gr.query();

while (gr.next())

{

gr.field_name = '<sysid 1>,<sysid 2>';

gr.update();

}

[sam43]

How  to keep the old user and add new user in the list field.

when i run the above script, old data is replacing with new one?

[SanjivMeher]

var gr = new GlideRecord('table_name');

gr.addQuery('<add query to update the number of records you want to update>');

gr.query();

while (gr.next())

{

if (gr.field_name)

gr.field_name =gr.field_name+ ',<sysid 1>,<sysid 2>';

else

gr.field_name = '<sysid 1>,<sysid 2>';

gr.update();

}