Command-Line Flags with Go-Lang

Kassim Damilola
Nov 3 · 1 min read

Command-line flags are a common way to specify options for command-line exercutable. Go provides a flag package supporting basic command-line flag parsing. This article shows how to pass CLI flag options to a running executable.

Flags are defined using flag.String(), Bool(), Int(), etc. Depending on the intended datatype.

First argument — Flag name
Second argument — Default value
Third argument — help message for flag name
instances := flag.Int(“instances”, 5, “number of deployed instance”)

After all flags are defined, call

flag.Parse()

to parse the command line into the defined flags.

Command line flag syntax

The following forms are permitted:

-flag
-flag=x
-flag x // non-boolean flags only
- h -> displays flag documentation
flag.png
$ go build flags.go
./flag -h
-instances int
number of deployed instances (default 5)
$ ./flags -instances 7
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