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Author SHA1 Message Date
jbranchaud
dce54bd689 Fix codeblock in recent TIL 2024-12-04 17:20:38 -06:00
jbranchaud
f1cc33fe40 Add Parse Flags From CLI Arguments as a Go TIL 2024-12-04 15:38:02 -06:00
3 changed files with 68 additions and 2 deletions

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@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
_1526 TILs and counting..._
_1527 TILs and counting..._
---
@@ -403,6 +403,7 @@ _1526 TILs and counting..._
- [Find Executables Installed By Go](go/find-executables-installed-by-go.md)
- [Not So Random](go/not-so-random.md)
- [Parse A String Into Individual Fields](go/parse-a-string-into-individual-fields.md)
- [Parse Flags From CLI Arguments](go/parse-flags-from-cli-arguments.md)
- [Replace The Current Process With An External Command](go/replace-the-current-process-with-an-external-command.md)
- [Sleep For A Duration](go/sleep-for-a-duration.md)
- [Upgrading From An Older Version On Mac](go/upgrading-from-an-older-version-on-mac.md)

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@@ -0,0 +1,65 @@
# Parse Flags From CLI Arguments
Though we can grab the arguments to a Go program from `os.Args`, it requires
some manual parsing. With the built-in `flag` package, we can declare specific
flags our program accepts, by type. When we parse them, they will be separated
out from the rest of the positional arguments.
Here is an example of the program that accepts a boolean `debug` flag. This
will work with either `-debug` or `--debug`.
```go
package main
import (
"flag"
"fmt"
"os"
)
func main() {
var debug bool
flag.BoolVar(&debug, "debug", false, "turns on debug mode, extra logging")
flag.Parse()
positionalArgs := flag.Args()
if len(positionalArgs) < 1 {
fmt.Println("Please specify which part to run: 1 or 2")
os.Exit(1)
}
if debug {
fmt.Println("We are in debug mode...")
fmt.Println("Received the following argument:", positionalArgs[0])
}
// ...
}
```
We can run the program in debug mode like so:
```bash
$ go run . --debug 123
We are in debug mode...
Received the following argument: 123
```
We can also take advantage of the `help` flag that we get for free:
```bash
$ go run . --help
Usage of /var/folders/62/lx9pcjbs1zbd83zg6twwym2r0000gn/T/go-build3212087168/b001/exe/test:
-debug
turns on debug mode, extra logging
```
Note: any recognized flags need to come before any of the position arguments.
The `debug` flag won't be picked up if we run the program like this:
```bash
$ go run . 123 --debug
```
[source](https://pkg.go.dev/flag)

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@@ -17,7 +17,7 @@ You can also manually create the TXT record if necessary.
Either way, it will look something like:
```bash
!dig -t TXT visualmode.dev
$ dig -t TXT visualmode.dev
;; ANSWER SECTION:
visualmode.dev. 377 IN TXT "google-site-verification=MBZ2S2fhnh2gHRxFniRrYW-O6mdyimJDRFj-f