Guidelines

Should bash variables be quoted?

Should bash variables be quoted?

General rule: quote it if it can either be empty or contain spaces (or any whitespace really) or special characters (wildcards). Not quoting strings with spaces often leads to the shell breaking apart a single argument into many. $? doesn’t need quotes since it’s a numeric value.

What are bash variables?

A variable in bash can contain a number, a character, a string of characters. You have no need to declare a variable, just assigning a value to its reference will create it.

What does quote mean in bash?

Quoting is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion.

What does %% mean in bash?

${PARAMETER%%PATTERN} This form is to remove the described pattern trying to match it from the end of the string. The operator “%” will try to remove the shortest text matching the pattern, while “%%” tries to do it with the longest text matching.

When to use a variable substitution in Bash?

Variable substitutions should only be used inside double quotes. Outside of double quotes, $var takes the value of var, splits it into whitespace-delimited parts, and interprets each part as a glob (wildcard) pattern. Unless you want this behavior, always put $var inside double quotes: “$var”.

How to double quote a variable in Bash?

The same applies to command substitutions: “$ (mycommand)” is the output of mycommand, $ (mycommand) is the result of split+glob on the output. echo “$var” # good echo “$ (mycommand)” # good another=$var # also works, assignment is implicitly double-quoted make -D THING=$var # BAD!

How to get the value of a variable in Bash?

For now, here are some things to remember: 1 A variable in single quotes ‘ is treated as a literal string, and not as a variable. 2 Variables in quotation marks ” are treated as variables. 3 To get the value held in a variable, you have to provide the dollar sign $. 4 A variable without the dollar sign $ only provides the name of the variable.

Why do you use quotation marks when assigning a variable in Bash?

If the value you assign to a variable includes spaces, they must be in quotation marks when you assign them to the variable. This is because, by default, Bash uses a space as a delimiter. Here’s an example: site_name=How-To Geek. Bash sees the space before “Geek” as an indication that a new command is starting.