SC2155 — Split declare and assign: fix in 30 seconds

Problem

When you combine `local`, `readonly`, `declare`, or `export` with a command substitution in one line, the exit code of the substitution is thrown away. The outer `local` or `export` always succeeds, so `set -e` will not catch a failing inner command and `$?` will report 0 even when `cmd` failed.

Bad

set -e
my_func() {
  local result=$(failing_command)   # always exits 0
  echo "$result"
}

Good

set -e
my_func() {
  local result
  result=$(failing_command) || return
  echo "$result"
}

Explanation

Splitting the declaration and assignment lets the assignment's own exit status (which equals the substitution's exit status) propagate. Now `set -e` aborts on failure and you can chain `|| return` or `|| handle_error` for explicit handling.

Related

SC2181

SC2086

When It Matters

declare, local, export, and readonly are commands, and their exit status is their own — not that of the command substitution inside the assignment. local out=$(failing_cmd) therefore succeeds even under set -e, and the script continues with an empty variable. In deployment scripts this converts a failed lookup into an empty path or an empty host name, which is then used as if it were valid.

Second Example

Exceptions

When the substitution cannot fail in any meaningful way — date, a pure parameter expansion, a literal — the combined form is harmless. It is still worth splitting for consistency, because the cost is one line and the failure mode is silent.

Faq