The balance command prints out the summarized balances of all my
top-level accounts, excluding sub-accounts.  In order to see the
balances for a specific account, just specify a regular expression
after the balance command:

@example
ledger balance expenses:food
@end example

This will show all the money that's been spent on food, since the
beginning of the ledger.  For food spending just this month
(September), use:

@example
ledger -p sep balance expenses:food
@end example

Or maybe you want to see all of your assets, in which case the -s
(show sub-accounts) option comes in handy:

@example
ledger -s balance ^assets
@end example

To exclude a particular account, use a regular expression with a
leading minus sign.  The following will show all expenses, but without
food spending:

@example
ledger balance expenses -food
@end example