String Variables & Quoting Rules

Single vs Double Quotes

Single quotes preserve text completely literally, so $name inside single quotes prints as the literal characters $name rather than being expanded. Double quotes still perform variable expansion, command substitution, and arithmetic expansion, while protecting the result from word splitting and globbing.

Example: Single vs Double Quotes

#!/bin/bash
name="Ada"
echo 'Hello, $name'
echo "Hello, $name"

Why Quoting Variables Matters

Leaving a variable unquoted lets Bash apply word splitting (breaking the value on spaces/tabs/newlines) and pathname expansion to it before the command sees it. Quoting the variable with double quotes keeps its value intact as a single argument, which is almost always what you want.

Warning: Unquoted $sentence collapses the multiple spaces into single spaces because word splitting discards extra whitespace; quoted "$sentence" preserves it exactly.

Example: Why Quoting Variables Matters

#!/bin/bash
sentence="multiple   words   here"
echo $sentence
echo "---"
echo "$sentence"

Escaping a Single Quote

Because nothing can be escaped inside single quotes, embedding a literal single quote requires closing the quoted string, inserting the quote character another way, and reopening the quoted string. The common idiom is '...'\''...', which closes, escapes one quote, then reopens.

Example: Escaping a Single Quote

#!/bin/bash
message='It'\''s a sunny day'
echo "$message"

Mixing Quotes and Expansions

It is common to combine literal text, variables, and command substitution inside a single double-quoted string, since double quotes allow all of Bash's expansions while still treating the whole thing as one argument. This keeps output readable without juggling many separate echo calls.

Example: Mixing Quotes and Expansions

#!/bin/bash
user="ada"
host=$(hostname)
echo "User $user is connected to $host at $(date +%H:%M:%S)"