Bash for Loops: Expansion Rules Explained

Bash for loops stop being confusing once you understand that the loop itself is simple—the complexity comes from how Bash expands words, globs, and command substitutions before the loop even runs. This article explains those expansion rules clearly, then shows you how to use them to write predictable loops.

Formula

The calculator above works out your average pace and speed for a run, ride, or walk. You enter the finish time in minutes and the distance in kilometers; the calculator returns your average pace in minutes per kilometer and your average speed in kilometers per hour.

The formulas are simple:

• Pace = finish time (min) ÷ distance (km)
• Speed = distance (km) ÷ (finish time (min) ÷ 60)

Where:

• t = finish time in minutes
• d = distance in kilometers
• pace = minutes per kilometer (min/km)
• speed = kilometers per hour (km/h)

Worked Example

Using the default values from the calculator (finish time = 50 minutes, distance = 10 km):

1. Pace = 50 ÷ 10 = 5.00 min/km
2. Speed = 10 ÷ (50 ÷ 60) = 10 ÷ 0.8333 = 12.00 km/h

The calculator shows the same results: 5.00 min/km and 12.00 km/h.

What the Result Means

Your pace tells you how many minutes it takes to cover one kilometer. A lower pace means you are moving faster. Your speed tells you how many kilometers you cover in one hour. These two numbers are just two ways of expressing the same performance—pace is useful for planning splits, while speed is handy for comparing with other activities or machines.

For example, a 5:00 min/km pace is the same as 12 km/h. If you run a 10 km race in 50 minutes, you held exactly that pace for the whole distance. If you run a 5 km in 25 minutes, your pace is also 5:00 min/km, but your speed is still 12 km/h—the distance does not change the relationship.

Common Mistakes

• Mixing units: If you enter distance in miles but the formula expects kilometers, your pace will be wrong. Convert miles to kilometers first (1 mile = 1.60934 km).
• Using seconds instead of minutes: If you enter a finish time of 3000 seconds instead of 50 minutes, the pace becomes 300 min/km. Always convert to minutes.
• Rounding too early: If you round the pace to 5.0 and then compute speed, you get 12.0, which is fine. But if you round 5.33 to 5.3 and then use it, your speed will be slightly off. Keep full precision until the final answer.

Limits of This Formula

This formula assumes a constant pace. In reality, you might start faster and slow down, or run hills and flats. The average pace is still useful, but it does not tell you about variations. For interval training or hilly routes, you might want to track each segment separately.

The formula also ignores rest stops, traffic lights, or terrain. If you stop for a minute at a water fountain, your moving pace is faster than your elapsed pace. Decide which one you want to measure and be consistent.

When to Use This Calculator

Use it to:

• Plan a race pace: if you want to finish a 10 km in under 50 minutes, you need to run faster than 5:00 min/km.
• Check a training run: after a run, enter your time and distance to see what pace you actually held.
• Compare activities: cycling at 20 km/h is not the same effort as running at 20 km/h, but the speed number lets you compare raw movement.

For treadmill runs, the distance is often shown in miles or kilometers. Make sure you enter the same unit as the formula.

Frequently Asked Questions

How do I convert pace to speed?

Divide 60 by the pace in minutes per kilometer. For example, 5:00 min/km → 60 ÷ 5 = 12 km/h. If your pace is 6:30 min/km, convert to decimal minutes (6.5) and divide: 60 ÷ 6.5 = 9.23 km/h.

What is a good running pace for a beginner?

It varies widely. A common conversational pace for a beginner might be 7:00–9:00 min/km (about 6.7–8.6 km/h). Focus on effort rather than a fixed number, and gradually increase distance before speed.

Does this work for walking?

Yes. Walking pace is often slower than 8:00 min/km, but the math is identical. Enter your walking time and distance to get your average walking pace and speed.

How do I calculate pace for miles?

Convert miles to kilometers first (1 mile = 1.60934 km). Then use the formula. If you want pace per mile instead, divide the time by the distance in miles directly, but the calculator here uses kilometers.

Why is my speed different from my treadmill’s reading?

Treadmills measure belt speed, not your actual pace. If you run at a slight incline or your stride varies, the treadmill’s number may differ from your real-world pace. Also, treadmill distance calibration can be off.

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in t | Finish time | min | 50 | 0
in d | Distance | km | 10 | 0 | 100000
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2