Bash Script Runtime Calculator

Work out bash script runtime instantly with clear inputs, formula shown and shareable results.

About Bash Script Runtime Calculator

Shell script performance is dominated by process creation, not by shell logic. A fork and exec costs around a millisecond while a builtin costs microseconds, so three external commands per iteration over 100,000 iterations spends six minutes forking. Replacing calls to cut, grep and sed with parameter expansion or a single awk invocation is where the gains are.

Formula

Script runtime

fork time = iterations x subprocesses x fork cost; builtin time = iterations x builtin cost; total = both

Worked example

With the default values below, Bash Script Runtime Calculator returns Estimated script runtime of 360.8. Change any input above and every figure here is recalculated in your browser.

Inputs used

Loop iterationsminimum 1: 100,000
External commands per iterationminimum 0: 3
Cost per process spawnminimum 0.001 ms: 1.2 ms
Cost per shell builtin operationminimum 0.01 us: 8 us

Results

Estimated script runtime: 360.8 s
Time spent forking external commands: 360.0 s
Time spent in shell builtins: 0.800 s
Share of runtime spent forking: 99.8%

Step by step

1Values used
2Script runtime
3Estimated script runtime= 360.8 s
4Time spent forking external commands= 360.0 s
5Time spent in shell builtins= 0.800 s
6Share of runtime spent forking= 99.8

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Which external commands are most worth eliminating?

Anything called inside a loop: basename, dirname, cut, expr, wc and seq all have builtin equivalents using parameter expansion or arithmetic.

When should the script be rewritten in another language?

Once it processes tens of thousands of records or needs data structures. Python or awk will run one to two orders of magnitude faster and be easier to maintain.