- go-for-perl-hackers
- Your editor
- Go vs Perl
- Comments
- Variables
- Lists
- Dumping Data Structures
- File Operations
- Flow Control
- Loops
- Functions
- Running Tests
- Debugging
- Sleep
- Parsing URIs
- Changing URI Query Params
- Command Line Scripts
The primary aim of this cheat sheet is to help Perl programmers get up and running with Go.
Consider adding the vim-go
plugin to your .vimrc
If you're using vim-plug, that would look something like:
Plug 'fatih/vim-go'
If you're using Pathogen, that would look something like:
runtime bundle/vim-pathogen/autoload/pathogen.vim
" Bundle: tpope/vim-pathogen
call pathogen#infect()
" Bundle: https://github.com/fatih/vim-go.git
Now, open vim
after installing vim-go
and enter :GoInstallBinaries
Also, you can add goimports
:
First install it: go get golang.org/x/tools/cmd/goimports
Then add the following to your .vimrc
let g:go_fmt_command = "goimports"
If your editor is set up to display tabs visually, you may want to disable that for Go files.
autocmd FileType go setlocal nolist
daf
in vim
will now allow you to cut an entire function without first
needing to select it.
go build
go run
go generate
Call this when your cursor is over something you'd like to rename, and it will be renamed in all of the appropriate locations.
Run this in order to test your code without leaving your vim
session.
Run this when inside a test function and only this test function will be run. Equivalent of go test -run MyFunctionName
.
Toggles file between foo.go
and foo_test.go
Takes you to the location where an item is defined. Keep running this to move further up the stack.
Pops the stack which you created with :GoDef
, taking you back to the previous location(s) you called :GoDef
from.
See functions which are declared in the current file.
Like :GoDecls
but finds all the functions declared in the directory of the file you're editing.
Find other places where a function or variable is being invoked.
Look up docs for a function.
Get a function's input and output parameters.
Like :GoInfo
, but with more info.
List all files in package.
List dependencies.
Get info on what sorts of errors an err
variable may contain.
Find out where a function callers are.
Generate stub methods required by an interface.
In this section we'll document some commonly used Perl constructs and try to find their equivalents in Go.
# single line
=pod
Multi line
=cut
// single line (C++-style)
/*
Multi-line (C-Style)
*/
print 'hello, world';
package main
import "fmt"
func main () {
fmt.Println("hello, world")
}
printf('We are open %i days per %s', 7, 'week');
package main
import ( "fmt" )
func main() {
fmt.Printf("We are open %d days per %s", 7, "week")
}
diag 'foo happens';
t.Log("foo happens")
t.Logf("We are open %d days per %s", 7, "week")
$ENV{FOO} = 'bar';
local $ENV{FOO} = 'bar'; # Same as above, but with local scope
print "GOPATH: $ENV{GOPATH}\n";
os.Setenv("FOO", "bar")
fmt.Println("GOPATH: ", os.Getenv("GOPATH"))
my $foo = 'bar';
my $pi = 3.14;
my $no_assignment;
// the following assignments are equivalent
var foo = "bar"
foo := "bar"
var pi float32 = 3.14 // explicit cast as float32
pi := float32(3.14) // explicit cast as float32
pi := 3.14 // implicit cast as float64
pi := "3.14" // implicit cast as string
var noAssignment string // equivalent to: noAssignment := ""
See golang.org/ref/spec#Rune_literals
my ($foo, $bar);
var foo, bar int
var nothing []string // create an empty slice
my ($i, $j) = (1, 2);
var i, j int = 1, 2
my $foo = 'bar'; // no variable interpolation
my $bar = "$foo baz"; // allow for variable interpolation
foo := "本" // implicitly cast as a string
foo := '本' // implicitly cast as a rune
my $long_string = <<'EOF';
my multiline
string
EOF
Use double quotes <<"EOF";
if you need to interpolate variables.
longString := `
my multiline
string
`
my $success = 1; # true
$success = 'foo'; # true
$success = 0; # false
$success; # (undef) false
if ($success) {
print "This succeeded";
}
if ( !$success ) {
print "This failed";
}
var success bool
success = true
success = false
if success == true {
fmt.Println("This succeeded")
}
if success {
fmt.Println("This succeeded")
}
if success == false {
fmt.Println("This failed")
}
if !success {
fmt.Println("This failed")
}
my $foo;
if ( ! defined $foo ) {
...;
}
var myString string
if myString == "" {
fmt.Println("Empty")
}
var mySlice []int
if mySlice == nil {
fmt.Println("nil")
}
See https://perldoc.perl.org/perlop.html#Auto-increment-and-Auto-decrement
$i = 0; $j = 0;
print $i++; # prints 0
print ++$j; # prints 1
$i = 0; $j = 0;
print $i--; # prints 0
print --$j; # prints -1
counter := 1
counter++
counter--
my $foo = 'go';
my $bar = 'pher';
$gopher = "$foo$bar";
$gopher = $foo . $bar;
$gopher = join q{}, $foo, $bar;
$gopher = sprintf '%s%s', $foo, $bar;
package main
import (
"fmt"
"strings"
)
func main() {
var gopher string
gopher = foo + bar
gopher = fmt.Sprintf("%s%s", foo, bar)
}
package main
import (
"fmt"
"strings"
)
func main() {
foo := "go"
bar := "pher"
gopher = strings.Join([]string{"go", "pher"}, "")
fmt.Println(gopher)
}
package main
import (
"bytes"
"fmt"
)
func main() {
var buffer bytes.Buffer
foo := "go"
bar := "pher"
buffer.WriteString(foo)
buffer.WriteString(bar)
fmt.Println(buffer.String())
}
use Const::Fast;
const my $hello => 'Hello, world';
// Create an *untyped* string constant
const hello = "Hello, world"
// Create a typed string constant
const hello string = "Hello, World"
Create multiple constants with one const
declaration:
const(
hello = "Hello, world"
goodbye = "Goodbye!"
)
Constants cannot be declared using the := syntax.
my @foo = (1..3);
my $first = $foo[0];
foo := [3]int{1,2,3}
first := foo[0]
Note that creating an empty array in Go means that it will be populated by the type's default values:
var bar [5]int \\ creates an array of [0,0,0,0,0]
my $size = @array;
size := len(array)
use Data::Printer; # exports p()
my %foo = (
X => 1,
Y => 2,
);
$foo{X} = 4;
print $foo{X}; # prints 4
p %foo;
# prints:
# {
# X => 4,
# Y => 2,
# }
delete $foo{X};
package main
import "fmt"
type Vertex struct {
X int
Y int
}
func main() {
v := Vertex{1, 2}
v.X = 4
fmt.Println(v.X) // prints 4
fmt.Printf("%+v\n", v) // prints {X:4 Y:2}
// additional examples
v1 = Vertex{1, 2} // has type Vertex
v2 = Vertex{X: 1} // Y:0 is implicit
v3 = Vertex{} // X:0 and Y:0
delete(v, "X")
}
my @foo = ('foo', 'bar', 'baz');
for my $value ( @foo ) {
print "$value\n";
}
my @foo = ('foo', 'bar', 'baz');
for (@foo) {
print "$_\n";
}
// Print array index for each element
my @foo = ('foo', 'bar', 'baz');
for my $i (0..$#foo) {
print "$i: $foo[$i]\n";
}
package main
import (
"fmt"
)
func main() {
foo := [3]int{1, 2, 3}
for i, v := range foo {
fmt.Printf("index: %v value: %v\n", i, v)
}
}
my @list = split ',', 'a,b,c'
package main
import (
"strings"
)
mySlice := strings.Split("a,b,c", ",")
my %hash = ( key_1 => 'foo', key_2 => 'bar', );
for my $key ( keys %hash ) {
printf( "key: %s value: %s\n", $key, $hash{$key} );
}
package main
import (
"fmt"
)
func main() {
myMap := map[string]string{"key1": "foo", "key2": "bar"}
for k := range myMap {
fmt.Printf("key: %s value: %s\n", k, myMap[k])
}
}
my %pages = ( home => 'https://metacpan.org' );
if ( exists $foo{home} ) {
...
}
https://stackoverflow.com/a/2050629/406224
package main
import "fmt"
func main() {
pages := make(map[string]string)
pages["home"] = "https://metacpan.org"
if _, ok := pages["home"]; ok {
fmt.Println("ok")
}
}
my %pages = ( home => 'https://metacpan.org' );
delete $pages{home};
package main
import "fmt"
func main() {
pages := make(map[string]string)
pages["home"] = "https://metacpan.org"
delete(pages, "home")
}
my %pages = ( home => 'https://metacpan.org' );
my @keys = keys %pages;
package main
func main() {
pages := make(map[string]string)
pages["home"] = "https://metacpan.org"
keys := []string{}
keys = append(keys, "foo")
}
my @array = (0..5);
my @slice = @list[2..4];
array := [6]int{0,1,2,3,4,5}
var slice []int = array[2:4]
var myslice []int // create an empty slice of integers
var nothing []string // create an empty slice of strings
Note that arrays in Go have a fixed size, whereas slices are dynamically sized.
Also:
A slice does not store any data, it just describes a section of an underlying array.
Changing the elements of a slice modifies the corresponding elements of its underlying array.
Other slices that share the same underlying array will see those changes.
See https://tour.golang.org/moretypes/8
Note also that slices in Go can use defaults for lower and upper bounds. That means that for the array of 10 integers var a [10]int
, the following slices are equivalent:
a[0:10] // explicit lower to upper bound
a[:10] // use default lower bound (0)
a[0:] // use default upper bound (0)
a[:] // use default upper and lower bounds (0 and 10)
Note that the lower bound is the starting point in the index (ie 0) and the length of the slice is the upper bound, which is why the entire slice consists of a[0:10
and not a[0:9]
.
See https://tour.golang.org/moretypes/10
my @array = (0..5);
my @slice = @list[2..4];
push @slice, 11, 12;
Note that in Perl, a slice of an array is also an array, so there's no need to make a distinction between the two.
array := [6]int{0,1,2,3,4,5}
var slice []int = array[2:4]
slice = append(slice, 11, 12)
use strict;
use warnings;
use feature qw( say );
use Data::Printer; # exports p() and np()
my %foo = ( a => 'b' );
p( %foo );
# or
say np( %foo );
package main
import "fmt"
func main() {
var config struct {
user string
pass string
}
config.user = "florence"
config.pass = "machine"
fmt.Printf("%+v", config)
return
}
Or:
package main
import "github.com/davecgh/go-spew/spew"
func main() {
var config struct {
user string
pass string
}
config.user = "florence"
config.pass = "machine"
spew.Dump(config)
return
}
use Data::Printer; # exports np()
use Path::Tiny qw(path);
my @list = ( 1..3 );
path('/tmp/foo.txt')->spew( np( @list ) );
package main
import (
"log"
"os"
"github.com/davecgh/go-spew/spew"
)
func main() {
list := [3]int{1, 2, 3}
file, err := os.OpenFile(
"/tmp/foo.txt",
os.O_CREATE|os.O_WRONLY,
0666,
)
if err != nil {
log.Fatal(err)
}
spew.Fdump(file, list)
file.Close()
}
use Data::Printer; # exports np()
use Path::Tiny qw(path);
my @list = ( 1..3 );
path('/tmp/foo.txt')->append( np( @list ) );
package main
import (
"log"
"os"
"github.com/davecgh/go-spew/spew"
)
func main() {
list := [3]int{1, 2, 3}
file, err := os.OpenFile(
"/tmp/foo.txt",
os.O_APPEND|os.O_CREATE|os.O_WRONLY,
0666,
)
if err != nil {
log.Fatal(err)
}
spew.Fdump(file, list)
file.Close()
}
use Path::Tiny qw( path );
use Try::Tiny qw( catch try );
my $dir = '.my-perl-cache';
try {
path($dir)->mkpath( { chmod => 0644 });
}
catch {
die sprintf "Could not create dir %s because of %s", $dir, $_;
};
package main
import (
"log"
"os"
)
func main() {
cacheDir := ".my-go-cache"
if err := os.MkdirAll(cacheDir, 0644); err != nil {
log.Printf("Cannot create dir %s because %v", cacheDir, err)
}
}
use Path::Tiny qw( path );
my $content = path('path', 'to', 'file')->slurp_utf8;
Note that in this case content
is []byte
content, err := ioutil.ReadFile(
filepath.Join("path", "to", "file")
)
if err != nil {
log.Fatal(err)
}
// convert byte array to string
contentAsString := string(content[:])
In the Perl example, we'll chomp the line to make explicit that newlines need to be handled.
use Path::Tiny qw( path );
my $first_line;
my $fh = path('/path/to/file')->openr_utf8;
while (my $line = <$fh>) {
$first_line = $line;
chomp $first_line;
last;
}
print $first_line, "\n";
scanner.Scan()
helpfully trims newlines for us.
import(
"fmt"
"log"
)
func main() {
file, err := os.Open("/path/to/file")
if err != nil {
log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
var firstLine string
for scanner.Scan() {
firstLine = scanner.Text()
break
}
if err := scanner.Err(); err != nil {
log.Fatal(err)
}
fmt.Println(firstLine)
}
if ( $foo > 1 ) {
print 'bar';
}
if ( foo > 1 ) {
fmt.Println("bar")
}
// parens are optional
if foo > 1 {
fmt.Println("bar")
}
if ( $foo > 1 ) {
print 'bar';
}
else {
print 'baz';
}
if foo > 1 {
fmt.Println("bar")
} else {
fmt.Println("baz")
}
if ( $foo > 1 ) {
print 'bar';
}
elsif ( $foo < 10 ) {
print 'baz';
}
if foo > 1 {
fmt.Println("bar")
} else if foo < 10 {
fmt.Println("baz")
}
my $sum;
for ( my $i = 0 ; $i < 10 ; $i++ ) {
$sum += $i;
}
sum := 0
for i := 0; i < 10; i++ {
sum += i
}
my $sum = 0;
my $i = 0;
while ( $i < 10 ) {
$sum += $i++;
}
// The init and post statement in a Go for loop are optional.
sum := 0
i := 0
for i < 10 {
sum += i
i += 1
}
while (1) {
}
for {
}
Perl:
while (1) {
...
next if $foo eq 'bar';
...
}
Go:
for {
if foo == "bar" {
continue
}
// Won't get here if continue is called
}
Note that continue
will immediately begin the next iteration of the innermost for
loop.
Perl:
while (1) {
...
last if $foo eq 'bar';
...
}
Go:
for {
if foo == "bar" {
break
}
// Won't get here if break is called
}
Note that break
will exit the enclosing loop at the point where it is called.
sub foo {
print 'ok';
}
foo();
package main
import "fmt"
func main() {
foo()
}
func foo() {
fmt.Println("foo")
}
$ perl Makefile.PL
$ make
$ make test
or
$ prove -l t/path/to/test.t
Use the -v
flag for verbose output:
$ prove -lv t/path/to/test.t
$ go test
Use the -v
flag for verbose output:
$ go test -v
If you're using vim-go
, use :GoTest
either from your foo.go
or
foo_test.go
. (Note, you can also use :GoAlternate
to toggle between the
two files.)
To test a subset of functions:
$ go test -run regexp
If you're using vim-go
, move your cursor to the name of the function you'd
like to test. Running :GoTest
here will run the function you're currently
in.
To bypass Go's test caching:
$ go test -count=1
use Carp qw( longmess );
print longmess();
package main
import (
"runtime/debug"
)
func main() {
debug.PrintStack()
}
sleep 60;
package main
import (
"time"
)
func main() {
time.Sleep(60 * time.Second)
}
use Mojo::URL ();
my $url = Mojo::URL->new('https://www.google.com/search?q=schitt%27s+creek');
print $url->query->param('q'); # schitt's creek
import (
"fmt"
"log"
"net/url"
)
func main() {
url, err := url.Parse("https://www.google.com/search?q=schitt%27s+creek")
if err != nil {
log.Fatal(err)
}
q := url.Query()
fmt.Println(q.Get("q")) // schitt's creek
}
package main
import (
"fmt"
"net/url"
)
func main() {
url, _ := url.Parse("https://example.com")
// Begin searches at today's date
q := url.Query()
q.Set("activity", "dance")
q.Set("type", "flash")
url.RawQuery = q.Encode()
fmt.Println(url)
}
print $ARGV[0], "\n" if $ARGV[0];
package main
import (
"fmt"
"os"
)
func main() {
if len(os.Args) > 1 {
fmt.Printf("%v\n", os.Args[1])
}
}
exit(0);
import("os")
os.Exit(0)