What is heredoc?

Heredoc syntax is a way to delimit strings in PHP (and other languages) with 3 “less than” symbols: <<<.

After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation.

The closing identifier must begin in the first column of the line. Also, the identifier must follow the same naming rules as any other label in PHP: it must contain only alphanumeric characters and underscores, and must start with a non-digit character or underscore.
PHP: Strings – Manual

An example may help:

<?php
echo <<<EOD
Example of string
spanning multiple lines
using heredoc syntax.
EOD;
?>

This will output:
“Example of string
spanning multiple lines
using heredoc syntax”

Not very impressive. However, where the handiness comes in is in the following:

Heredoc text behaves just like a double-quoted string, without the double quotes. This means that quotes in a heredoc do not need to be escaped. Variables are expanded, but the same care must be taken when expressing complex variables inside a heredoc as with strings.
PHP: Strings – Manual

This allows you to use variables and quotes in your heredocs without having to escape every single quote you want to use. It makes it very useful for printing out extremely long strings of text.

Things to remember about using heredoc

Heredocs are a great way to simplify your code and print out long strings. Here is just a few things to keep in mind when using them:

• Heredocs start with “<<<IDENTIFIER where IDENTIFIER must follow the same naming conventions of PHP variables.
• The closing identifier must be the same as the opening identifier
• The line with the closing identifier must contain no other characters, except possibly a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs before or after the semicolon
• Quotes and double quotes do not need to be escaped
• Variables are expanded

For more information, refer to the PHP: Strings Manual on php.net

Bonus: Heredocs for bash scripting

Heredocs for bash work pretty much the exact same way as they do for PHP but are delimited by 2 “less than” symbols:” << instead of 3. Here is a handy way to output large fields of text into a file through a bash script:

#!/bin/bash
cat <<OUTPUT > /etc/my.cnf
[mysqld]
socket=/tmp/mysql.sock
port=3306
user=mysql
password=supersecretpassword
log-bin=mysql-bin
server-id=1
OUTPUT

What about you? What new things have you learned from reading other peoples’ code? Share with us and we’ll all learn something new.

array=( ${array[@]-} $(echo "$variable") )

The code above reads as follows:

array=( ….. ) : Set your array variable named, appropriately enough: array.

${array[@]-} : Read all variables from the array array. The hyphen at the end prevents an “unbound variable” error when -u or -o nounset is set and array is an empty array. This is useful for appending the first value to an empty array in the event that one of the aforementioned flags is set.

$(echo “$variable”) : Add the variable $variable to the array through the use of command substitution $(…) by reading the output of echo “$variable” as the input value for the array. The reason for command substitution is that if you try it without the $(…), bash will read echo and “$variable” as separate entries into the array instead of just the value of $variable