Quoting

Core Idea

Quoting controls how Bash turns text into command arguments.

Most shell bugs are not command bugs. They are argument bugs caused by word splitting, glob expansion, or variables expanding at the wrong time.

Quote variables by default:

printf '%s\n' "$name"

Leave a variable unquoted only when you intentionally want Bash to split it or expand patterns.

Single quotes preserve text exactly. Bash does not expand variables inside them.

printf '%s\n' '$HOME'

Output:

$HOME

Use single quotes for grep, sed, and awk programs unless you deliberately need shell expansion.

Double quotes preserve spaces but still allow variable and command substitution.

name='Ada Lovelace'
printf 'Hello %s\n' "$name"

Without quotes, Bash would split the name into two arguments.

Backslash protects one character or creates escapes interpreted by a command.

printf 'line one\nline two\n'
grep '\.org$' urls.txt

In the grep example, \. means a literal dot in the regular expression.

Quote command substitution too:

printf 'today=%s\n' "$(date +%F)"

Shell globs expand before the command runs:

ls *.md

Quote a glob when you want the receiving command to see the pattern literally:

find ~/src -name '*.md'

Set name='Ada Lovelace', print it quoted and unquoted with printf '[%s]\n', then explain the difference.