_output.txt

 $ run_test simple 1024 1024
 $ local name=simple
 $ shift
 $ local first_size=1024
 $ shift
 $ local second_size=1024
 $ shift
 $ local start=1024
 $ rm -f simple.img
 $ truncate -s 3072KiB simple.img
 $ ls -lh simple.img
-rw-r--r-- 1 samuel users 3.0M Sep  3 17:50 simple.img
 $ ls -l simple.img
-rw-r--r-- 1 samuel users 3145728 Sep  3 17:50 simple.img
 $ cat
 $ cat script.sfdisk
label: dos
label-id: 0x012345678
start=1024KiB, size=1024KiB
start=2048KiB, size=1024KiB
 $ sfdisk simple.img
Checking that no-one is using this disk right now ... OK

Disk simple.img: 3 MiB, 3145728 bytes, 6144 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

>>> Script header accepted.
>>> Script header accepted.
>>> Created a new DOS disklabel with disk identifier 0x12345678.
simple.img1: Created a new partition 1 of type 'Linux' and of size 1 MiB.
simple.img2: Created a new partition 2 of type 'Linux' and of size 1 MiB.
simple.img3: Done.

New situation:
Disklabel type: dos
Disk identifier: 0x12345678

Device      Boot Start   End Sectors Size Id Type
simple.img1       2048  4095    2048   1M 83 Linux
simple.img2       4096  6143    2048   1M 83 Linux

The partition table has been altered.
Syncing disks.
 $ rm script.sfdisk
 $ run_test complex 13312 1024
 $ local name=complex
 $ shift
 $ local first_size=13312
 $ shift
 $ local second_size=1024
 $ shift
 $ local start=1024
 $ rm -f complex.img
 $ truncate -s 15360KiB complex.img
 $ ls -lh complex.img
-rw-r--r-- 1 samuel users 15M Sep  3 17:50 complex.img
 $ ls -l complex.img
-rw-r--r-- 1 samuel users 15728640 Sep  3 17:50 complex.img
 $ cat
 $ cat script.sfdisk
label: dos
label-id: 0x012345678
start=1024KiB, size=13312KiB
start=14336KiB, size=1024KiB
 $ sfdisk complex.img
Checking that no-one is using this disk right now ... OK

Disk complex.img: 15 MiB, 15728640 bytes, 30720 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

>>> Script header accepted.
>>> Script header accepted.
>>> Created a new DOS disklabel with disk identifier 0x12345678.
complex.img1: Created a new partition 1 of type 'Linux' and of size 13 MiB.
complex.img2: All space for primary partitions is in use.
Failed to add #2 partition: Invalid argument
Leaving.

weird-sfdisk.sh

#!/usr/bin/env bash

set -e
set -u
PS4=" $ "
set -x

run_test() {
	local name=$1        ; shift
	local first_size=$1  ; shift
	local second_size=$1 ; shift
	local start=1024
	rm -f "$name.img"
	truncate -s $((start+first_size+second_size))KiB "$name.img"
	ls -lh "$name.img"
	ls -l "$name.img"
	cat > script.sfdisk <<-EOF
	label: dos
	label-id: 0x012345678
	start=$((start))KiB, size=$((first_size))KiB
	start=$((start+first_size))KiB, size=$((second_size))KiB
	EOF
	cat script.sfdisk
	sfdisk "$name.img" < script.sfdisk
	rm script.sfdisk
}

# Simple, two parts, each 1MiB.
run_test simple  1024 1024

# 13MiB, so should stay aligned both to MiB and sectors.
# Somehow the second partition can't be created!
run_test complex $((1024 * 13)) 1024