Confusing string concatenation from stray quotes

Problem

Adjacent quoted and unquoted fragments such as `"-l""$dir""/file"` or `"a"$b"c"` concatenate into one word — that part is valid — but the alternating quote/no-quote pattern is a strong signal of a mistake: often a missing space, a stray extra quote, or a misunderstanding that quotes are needed around each embedded piece rather than around the whole expression. Even when the result happens to be correct, this style is hard to read and easy to get wrong the next time it is edited, since it is unclear at a glance where one "argument" ends and another begins.

Bad

path="-l""$dir""/config.conf"
echo $path

Good

path="-l$dir/config.conf"
echo "$path"

Explanation

Bash concatenates adjacent strings/expansions into a single word whether or not each piece is separately quoted, so wrapping the whole expression in one pair of quotes is both sufficient and far more readable. Reserve separate quoted segments for cases where you are genuinely building up multiple distinct arguments.

Related

SC2086

SC2027

SC2089

When It Matters

Adjacent quoted and unquoted sections concatenate silently, so "a"b"c" is one word — and a stray quote in the middle of an argument produces a value that is almost right. The usual result is a path or URL with a missing or doubled character that only fails at the point of use. ShellCheck flags the pattern because it is far more often a typo than a deliberate concatenation.

Second Example

Exceptions

Mixing quote styles on purpose is legitimate when part of the string must stay literal, for example an awk program combined with a shell value. Keep those cases short and comment them, since the reader has to reason about three quoting contexts at once.

Faq