Perl and Go equivalents

This is a list of equivalents in Perl and Go, meant as a quick start for a Perl programmer learning Go.

Variables

🐫 Perl

♫ Notes

my $x

var x {}interface

In Go, {}interface can contain a general quantity. However, basically Go does not have untyped variable.

my $x = \$y

x := & y

my %x;

x := map[string]string

In Go, the type of the value of the hash needs to be explicitly specified. Here := explicitly creates the variable x.

Functions

🐫 Perl

♫ Notes

my (undef, $x) = f ();

_, x := f()

An underscore is used in Go to discard return values of a function, similar to assigning to undef in Perl.

defined $x{key}

_, ok = x["key"]

In Go, a second argument when retrieving from a map returns a boolean which is equivalent to defined in Perl.

×

var x bool
y := false

Perl does not have any native boolean type.

$x = 99;
if ($x) {

}

x := 99
if x > 0 {

}

Go doesn't allow anything but actual booleans in if statements. Empty strings must be tested for using len statements, as in if len(s) == 0.

use utf8;

×

All Go strings and identifiers are in UTF-8, so it is as if "use utf8;" in Perl was on by default. To get a non-utf-8 "string" in Go, one uses []byte rather than string.

$x =~ tr/a/x/;

x = strings.Map(
func(a rune) rune {
if a == 'a' { return 'x'}
}, x)

In Go, strings.Map requires a function which maps from rune to rune.

map { f ($_) } split //, $s

strings.Map(s, f)

Arrays / slices

🐫 Perl

♫ Notes

my @x = (1, 2, 3);

var x [3]int
y := (1, 2, 3)

Arrays are fixed size and are rarely used in Go. Slices (similar to array references in Perl) are much more common.

my @x = (1, 'two', $three);

Go slices must have a type and they can only contain one type.

my $y = scalar @x

y := len(x)

push @a, $b

a = append(a, b)

append monkeys with the "underlying array" which means that all kinds of unexpected things might happen if you are not careful.

push @a, @b

a = append(a, b...)

In Go, it's possible to append one slice to another slice, but an ellipsis is necessary.

my $x = pop @a;

x := a[len(a)-1]
a = a[0:len(a)-1]

Go requires you to chop the end of the slice off yourself.

for my $y (@x)

for _, y := range x

for my $i (0..$#x) {
    my $y = $x[$i];

for i, y := range x {

The first argument returned by range is the index into the array.

ref $x

import "reflect"
...
reflect.Type(x)

The Go method requires the package "reflect" to be imported.

caller

runtime.Caller

×

cap(x)

Go's cap, the capacity of an array, has no simple equivalent in Perl. There are modules like Devel::Peek which might allow you to find the allocated size of an array, but it won't be very much use anyway.

Input/output

🐫 Perl

♫ Notes

printf "%s", $x;

fmt.Printf("%s", x)

printf $fh "%s", $x;

fmt.Fprintf(fh, x)

say $x;

fmt.Println(x)

Strings

🐫 Perl

♫ Notes

my $x = 'abc';
my $y = "abc";

x := "abc"

x := 'a' is valid in Go, but it defines a variable which can only hold a single character, a "rune".

my $cat = 'a' . "b" . $c;

cat := "a" + "b" + c

String concatenation is via @go{+} in Go.

my $multiline = <<EOF;
Multi
Line
String
EOF

multiline := `
Multi
Line
String
`

substr $x, 10, 10

x[10:20]

In Go, use slices to get substrings. The numbers in Go are always offsets, whereas the second number in Perl is a length.

sprintf ("%d %X %s\n", $a, $b, $c);

fmt.Sprintf("%d %X %s\n", a, b, c)

use utf8;
my $key = '猿蛇月金飛行機';
my $snake = substr ($key, 1, 1);

key := "猿蛇月金飛行機"
snake := key[3:6]

Go uses byte offsets into strings, there is no attempt to fake up a "single character". Go's regexp package has two different sets of functions for @go{[]byte} and @go{string} variables.

use utf8;
my $key = '猿蛇月金飛行機';
say length $key;

key := "猿蛇月金飛行機"
fmt.Println(len([]rune(key)))

To count UTF-8 entities ("runes") in Go, cast the string to a slice of runes. There is also a package function unicode/utf8.RuneCount.

my %x;

x := make(map[string]string)

Go has associative arrays but the type needs to be specified. A general associative array in Go has the type map[string]{}interface.

$s = lc $s

s = strings.ToLower(s)

$s = uc $s

s = strings.ToUpper(s)

$s = ucfirst $s;

s = strings.Title(s)

The Go function splits s and "title cases" each word.

join

strings.Join

Go requires the strings package to be imported.

my $repeat = 'abc' x 42

repeat := strings.Repeat("abc", 42)

$v:string =~ s/\Q$old/$new/

strings.Replace(s, old, new, 1)

$v:string =~ s/\Q$old/$new/g

strings.Replace(s, old, new, -1)
strings.ReplaceAll(s, old, new)

Regexes

🐫 Perl

♫ Notes

quotemeta

regexp.QuoteMeta

$z =~ s/this/that/;

r := regexp.MustCompile(`(this)`)
z = r.ReplaceAllString(z, "that")

Imports

🐫 Perl

♫ Notes

use Module;

import "module"

package Module;

package module

use Exporter;
@EXPORT = qw!func_a func_b func_c!

func A() {

}

To export a function from a Go package, give its name a capital letter. To not export it, make the first letter of its name lower case.

Web encodings

🐫 Perl

♫ Notes

Uri::Escape/uri_escape

net/url.QueryEscape

HTML::Entities/encode_entities

html.EscapeString

Control

🐫 Perl

♫ Notes

elsif

else if

Go does not have an elsif statement.

if ($x eq $y) {
if ($x == $y) {

if x == y {

Go does not have anything like eq and friends in Perl, strings are compared using ==. Similarly for ne and so on.

||, &&
or, and

||, &&

Go does not have anything like or and friends in Perl.

next

continue

last

break

next label

continue label

last label

break label

goto label

goto label

Other

🐫 Perl

♫ Notes

perltidy

go fmt, gofmt

Go has only one formatting option.

perlcritic

go vet

Web links

go-for-perl-hackers
Go for Perl hackers, github repository by Olaf Alders

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