OLDIFS=$IFS

I forgot to set it back at the end of my one-liner, which caused some problems for me. I tried checking another server to see what the default is, but if you just run the command

# echo $IFS
#

you see that you just get a blank line. The way to show all non-printing characters is to pipe the output into cat with a couple of switches.

# echo "$IFS" | cat -vTE
 ^I$
$
#

The switches stand for the following:

-v, –show-nonprinting

use ^ and M- notation, except for LFD and TAB

-T, –show-tabs

display TAB characters as ^I

-E, –show-ends

display $ at end of each line

**Note -t can be substituted for -vT; -e can be substituted for -vE

So our output above, indicates that the default setting for the $IFS variable is: a space, followed by a tab, followed by a new line character.

Once I had this information, it was very easy to then reset the $IFS variable back to it’s default. While trying to set this, I had problems with the tab (for some reason it wasn’t registering) so I just wrote it as ‘^I’. Once set, run the

echo "$IFS" | cat -vTE

command again to verify and make sure it matches the output above and you’ll be all set.

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

I have also included numerous shortcuts/key combinations for the vi/vim text editor. This may turn into it’s own cheat sheet in the near future if I continue to add to it due to the amount of info I have for vi alone. Time will tell.

You can view my Linux Command-Line Cheat Sheet here. If you have additional commands for one of the topics posted, or have a topic you would like to see added, leave a comment on that post and I will get it added.

**Note: awk is currently on that list although I have not added any info for it yet as it is an extremely extensive command and I am still working my way through the info I want to add. In fact, entire books have been written
about awk alone.