[shell] Shell command to sum integers, one per line?

dc -f infile -e '[+z1<r]srz1<rp'

Note that negative numbers prefixed with minus sign should be translated for dc, since it uses _ prefix rather than - prefix for that. For example, via tr '-' '_' | dc -f- -e '...'.

Edit: Since this answer got so many votes "for obscurity", here is a detailed explanation:

The expression [+z1<r]srz1<rp does the following:

[   interpret everything to the next ] as a string
  +   push two values off the stack, add them and push the result
  z   push the current stack depth
  1   push one
  <r  pop two values and execute register r if the original top-of-stack (1)
      is smaller
]   end of the string, will push the whole thing to the stack
sr  pop a value (the string above) and store it in register r
z   push the current stack depth again
1   push 1
<r  pop two values and execute register r if the original top-of-stack (1)
    is smaller
p   print the current top-of-stack

As pseudo-code:

1. Define "add_top_of_stack" as:
   1. Remove the two top values off the stack and add the result back
   2. If the stack has two or more values, run "add_top_of_stack" recursively
2. If the stack has two or more values, run "add_top_of_stack"
3. Print the result, now the only item left in the stack

To really understand the simplicity and power of dc, here is a working Python script that implements some of the commands from dc and executes a Python version of the above command:

### Implement some commands from dc
registers = {'r': None}
stack = []
def add():
    stack.append(stack.pop() + stack.pop())
def z():
    stack.append(len(stack))
def less(reg):
    if stack.pop() < stack.pop():
        registers[reg]()
def store(reg):
    registers[reg] = stack.pop()
def p():
    print stack[-1]

### Python version of the dc command above

# The equivalent to -f: read a file and push every line to the stack
import fileinput
for line in fileinput.input():
    stack.append(int(line.strip()))

def cmd():
    add()
    z()
    stack.append(1)
    less('r')

stack.append(cmd)
store('r')
z()
stack.append(1)
less('r')
p()