ERROR: COPY delimiter must be a single one-byte character

If you are using Vertica, you could use E'\t'or U&'\0009'

To indicate a non-printing delimiter character (such as a tab), specify the character in extended string syntax (E'...'). If your database has StandardConformingStrings enabled, use a Unicode string literal (U&'...'). For example, use either E'\t' or U&'\0009' to specify tab as the delimiter.

Unfortunatelly there is no way to load flat file with multiple characters delimiter ~,~ in Postgres unless you want to modify source code (and recompile of course) by yourself in some (terrific) way:

/* Only single-byte delimiter strings are supported. */
if (strlen(cstate->delim) != 1)
    ereport(ERROR,
        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
    errmsg("COPY delimiter must be a single one-byte character")));

What you want is to preprocess your input file with some external tool, for example sed might to be best companion on GNU/Linux platfom, for example:

sed s/~,~/\\t/g inputFile

The obvious thing to do is what all other answers advised. Edit import file. I would do that, too.

However, as a proof of concept, here are two ways to accomplish this without additional tools.

1) General solution

CREATE OR REPLACE FUNCTION f_import_file(OUT my_count integer)
  RETURNS integer AS
$BODY$
DECLARE
    myfile    text;  -- read xml file into that var.
    datafile text := '\path\to\file.txt'; -- !pg_read_file only accepts relative path in database dir!
BEGIN

myfile := pg_read_file(datafile, 0, 100000000);  -- arbitrary 100 MB max.

INSERT INTO public.my_tbl
SELECT ('(' || regexp_split_to_table(replace(myfile, '~,~', ','), E'\n') || ')')::public.my_tbl;

-- !depending on file format, you might need additional quotes to create a valid format.

GET DIAGNOSTICS my_count = ROW_COUNT;

END;
$BODY$
  LANGUAGE plpgsql VOLATILE;

This uses a number of pretty advanced features. If anybody is actually interested and needs an explanation, leave a comment to this post and I will elaborate.

2) Special case

If you can guarantee that '~' is only present in the delimiter '~,~', then you can go ahead with a plain COPY in this special case. Just treat ',' in '~,~' as an additional columns. Say, your table looks like this:

CREATE TABLE foo (a int, b int, c int);

Then you can (in one transaction):

CREATE TEMP TABLE foo_tmp ON COMMIT DROP (
 a int, tmp1 "char"
,b int, tmp2 "char"
,c int);

COPY foo_tmp FROM '\path\to\file.txt' WITH DELIMITER AS '~';

ALTER TABLE foo_tmp DROP COLUMN tmp1;
ALTER TABLE foo_tmp DROP COLUMN tmp2;

INSERT INTO foo SELECT * FROM foo_tmp;

Not quite sure if you're looking for a postgresql solution or just a general one.

If it were me, I would open up a copy of vim (or gvim) and run the commend :%s/~,~/~/g
That replaces all "~,~" with "~".

you can use a single character delimiter, open notepad press ctrl+h replace ~,~ with something will not interfere. like |