Excel extract substring from string

This problem can be broken down into two steps:

1. Find the index in the string of your desired split character (in this case, "-" or " - ").
2. Get the prefix substring from the beginning of the original text to the split index.

The FIND and SEARCH commands each would return the index of a given needle in a haystack (FIND is case-sensitive, SEARCH is case-insensitive and allows wildcards). Given that, we have:

FIND(search_text, source_cell, start_index)

or in this case:

FIND(" - ", A1, 1)

Once we have the index, we need the prefix of source_cell to do the "split". MID does just that:

MID(source_cell, start_index, num_characters)

Putting them both together, we have:

=MID(A1,1,FIND(" - ",A1,1))

with A1 having text of ABC - DEF gives ABC.

Expanding upon Andrew's answer based on your edit: to find the character string to split at, we are using the FIND function. If the FIND fails to locate the string given, it returns a #VALUE? error. So we will need to check for this value and use a substitute value instead.

To check for any error value including #VALUE, we use the ISERROR function, thus:

=ISERROR(FIND(" - ", A1, 1))

that will be true if the FIND function can't find the " - " string in the A1 cell. So we use that to decide which value to use:

=IF(ISERROR(FIND(" - ", A1, 1)), A1, MID(A1, 1, FIND(" - ", A1, 1)))

That says that if the find command returns an error, use the unmodified A1 cell. Otherwise, do the MID function that Andrew already provided.