Accumulation
Suppose we have two files,
deposits
and
withdrawals,
of records containing a name field and an amount field.
For each name we want to print the net balance determined by
subtracting the total withdrawals from the total deposits for each name.
The net balance can be computed by the following program:
awk '
FILENAME == "deposits" { balance[$1] += $2 }
FILENAME == "withdrawals" { balance[$1] -= $2 }
END { for (name in balance)
print name, balance[name]
} ' deposits withdrawals
The first statement uses the array
balance
to accumulate the total amount for each name in the file
deposits.
The second statement subtracts associated withdrawals
from each total.
If only withdrawals are associated with a name,
an entry for that name is created by the second statement.
The
END
action prints each name with its net balance.
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