In Bash, quoting controls whether characters are treated as syntax or literal data. Use single quotes for completely literal text, double quotes to allow selected expansions while preventing word splitting and pathname expansion, a backslash to protect one character, and ANSI-C quoting ($'...') when you need escapes such as a newline. Correct quoting keeps file names, variable values, and command arguments intact.
The rules below follow the GNU Bash Reference Manual for Bash 5.3 (updated 18 May 2025). Some forms, especially ANSI-C quoting, are Bash features and should not be assumed to work in a strictly POSIX sh script.
What Bash quoting does
Before Bash runs a command, it recognizes shell syntax, performs expansions, splits unquoted results into words, expands unquoted wildcard patterns, and removes the quotes themselves. Quoting changes which characters participate in those stages. It does not add quote characters to the argument received by the command.
For example, these commands pass different arguments:
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printf '<%s>n' one two
printf '<%s>n' "one two"
printf '<%s>n' 'one two'The first command supplies two arguments; the other two supply one argument containing a space.
The four Bash quoting mechanisms
Backslash: protect the next character
An unquoted backslash removes the special meaning of the character immediately after it. This is useful for one space, dollar sign, wildcard, quote, or other metacharacter:
printf '%sn' file name
printf '%sn' $HOME
printf '%sn' *.logA backslash followed by a newline is removed entirely. Bash therefore treats the next physical line as a continuation of the current command:
printf '%sn' first
secondInside double quotes, backslash retains special meaning only before $, backtick, double quote, backslash, or newline. Before other characters it remains literal. Inside single quotes, a backslash has no special meaning at all.
Single quotes: make every character literal
Between single-quote characters, every character retains its literal value. Variables, command substitutions, backslashes, wildcards, and whitespace are not interpreted:
name='Ada $USER'
printf '%sn' '$HOME' '*.txt' '$(date)'Those examples print the characters $HOME, *.txt, and $(date), rather than expanding them.
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A single quote cannot appear inside a single-quoted span, even when preceded by a backslash. End the span, add an escaped or differently quoted quote, and then reopen it:
message='It'7s Bash'
printf '%sn' "$message"Here the adjacent pieces produce It's Bash. Another readable option is to use double quotes when the text contains a single quote but no expansion that you want to suppress:
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message="It's Bash"For arbitrary text that may contain both quote types, store pieces in variables or use a quoted here-document rather than trying to place an unescaped delimiter inside single quotes.
Double quotes: protect a word but permit selected expansions
Double quotes preserve the literal value of most characters and keep the result as one shell word. They still allow:
- parameter expansion, such as
$nameor${name}; - command substitution, such as
$(date)or legacy backticks; - arithmetic expansion, such as
$((count + 1)); - backslash escapes for
$, backtick, double quote, backslash, and newline.
name='Ada Lovelace'
printf 'Hello, %sn' "$name"
printf 'Today is %sn' "$(date +%F)"Double-quote expansions whenever you want one argument. Without quotes, a value containing spaces, tabs, newlines, or wildcard characters can become multiple arguments or expand to matching pathnames.
file='notes from Monday.txt'
cat -- "$file" # one filename argument
cat -- $file # usually several words; may also globUse "$@" to forward positional parameters one by one, preserving each argument. "$*" instead joins the positional parameters into one word using the first character of IFS (a space by default).
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ANSI-C quoting: $'...'
Bash’s ANSI-C quoting expands backslash escapes inside the quoted text, then treats the resulting value as one word. Common escapes include n for a newline, t for a tab, \ for a backslash, ' for a single quote, and " for a double quote.
printf '%s' $'first linensecond linen'
quote=$'It's quoted'The exact escape repertoire is Bash-specific; do not use this form when the script must run under an implementation that only promises POSIX sh.
Single quotes versus double quotes
| Form | Parameter, command, and arithmetic expansion | Word splitting and pathname expansion | Typical use |
|---|---|---|---|
'text' |
No | No | Completely literal text |
"text" |
Yes | No for the quoted result | One argument containing a variable or substitution |
x |
Protects only the next character | Depends on the rest of the word | Escape one metacharacter or space |
$'text' |
Backslash escape processing | No for the resulting quoted word | Newlines, tabs, and special characters in Bash scripts |
How quoting stops variable expansion
To print a dollar sign literally, either single-quote it or escape it:
printf '%sn' '$HOME'
printf '%sn' $HOMETo expand a variable safely, use double quotes around the expansion:
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printf 'Path: %sn' "${HOME}/bin"Braces delimit the variable name when adjacent characters could otherwise be interpreted as part of it. They do not replace quoting:
prefix='report'
printf '%sn' "${prefix}_2026.txt"Command and arithmetic substitutions follow the same rule: quote the complete substitution when its output must remain one argument.
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result="$(some_command)"
printf '%sn' "$result"
count=$((width * height))Why a quoted variable can still behave unexpectedly
Only the expansion is quoted
Quoting one expansion does not quote other text in the same word. Keep the entire argument in one pair of double quotes:
dir='/tmp/my files'
rm -- "$dir"/*.tmpIn this example, the directory value is protected, while the final *.tmp is intentionally left unquoted so Bash can perform pathname expansion. Quote the pattern too when you want a literal asterisk:
printf '%sn' "$dir/*.tmp"Arrays require the right expansion
For an array, "${items[@]}" expands to one word per element, preserving empty elements and embedded whitespace. "${items[*]}" expands to one word containing all elements joined by the first IFS character.
items=('red blue' green '')
printf '<%s>n' "${items[@]}"
printf '<%s>n' "${items[*]}"Quoting cannot undo an earlier transformation
If data was already split, glob-expanded, or interpreted as shell code before it reached a variable, adding quotes later cannot reconstruct the original text. Do not build a command string and then execute it with eval unless you have a compelling, carefully audited reason. Prefer arrays for commands and arguments:
cmd=(grep --fixed-strings -- 'a b' 'notes/*.txt')
"${cmd[@]}"Quoting common special characters
- Whitespace: use
"a b",'a b', or escape the space asa b. - Wildcard characters: quote
*,?, and bracket expressions when they must remain literal. - Semicolon, pipe, ampersand, redirection, and parentheses: quote or escape them when they are data rather than shell operators.
- Hash: an unquoted
#can begin a comment where Bash recognizes a comment; quote it when it is part of data. - Newline: use
$'n', a quoted here-document, or a variable containing a newline rather than an accidental command terminator.
printf '%sn' 'a; b | c & d > file'
printf '%sn' 'literal *.log'Quotes in here-documents
A here-document delimiter controls whether its body is expanded. With an unquoted delimiter, parameter expansion, command substitution, arithmetic expansion, and backslash processing can occur in the body:
cat <<EOF
User: $USER
EOFQuote any part of the delimiter to suppress those expansions and pass the body literally:
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cat <<'EOF'
User: $USER
$(date)
EOFThe closing delimiter must appear by itself at the start of a line (subject to the here-document indentation options you explicitly use). A quoted delimiter is especially useful for configuration files, scripts, and examples that contain dollar signs.
Practical quoting patterns
Pass a filename safely
filename=$1
if [[ -e $filename ]]; then
printf 'Found: %sn' "$filename"
fiWithin Bash’s [[ ... ]] conditional syntax, ordinary word splitting and pathname expansion are not performed in the same way as in ordinary command arguments, but quoting variable expansions remains a clear and portable habit, especially when the value is reused outside [[ ]].
Read lines without losing whitespace
while IFS= read -r line; do
printf '<%s>n' "$line"
done < input.txtread -r prevents backslash interpretation, and quoting "$line" preserves the line’s whitespace when it is printed.
Use a literal regular-expression or search pattern
pattern='[draft] $HOME'
grep --fixed-strings -- "$pattern" notes.txtSingle quotes make the assignment literal; double quotes preserve the resulting pattern as one argument.
Quoting checklist
- Do you want literal text with no expansion? Use single quotes.
- Do you need variable or command expansion but one argument? Use double quotes.
- Do you need a newline, tab, or escaped quote in Bash? Consider
$'...'. - Are you escaping only one metacharacter? A backslash may be simplest.
- Could a value contain spaces, newlines, wildcard characters, or be empty? Quote its expansion.
- Are you forwarding script arguments? Use
"$@", not unquoted$@. - Are you constructing a command? Use an array instead of a string and avoid
eval. - Should a here-document be literal? Quote its delimiter.
Frequently Asked Questions
How do I include a single quote inside a Bash single-quoted string?
End the single-quoted span, add the quote using another quoted or escaped segment, and reopen it: 'It'''s' produces It's. For simple text, double quotes or $'...' may be clearer.
What is the safest way to expand a Bash variable?
Use double quotes around the expansion, such as "$value" or "${dir}/file", unless you deliberately need word splitting or pathname expansion.
Why does echo "$var" still show a wildcard or dollar sign literally?
Double quotes allow parameter, command, and arithmetic expansion, but they do not recursively interpret the characters produced by a variable as new shell syntax. A value containing * or $ remains data.
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