SC2155: Declare and Assign Separately to Preserve Exit Codes

The Hidden Bug in local var=$(command)

When you combine local (or export, declare) with a command substitution, the exit status of the command is replaced by the exit status of the local keyword — which is almost always 0 (success).

The Problem

my_function() {
  local result=$(failing_command)  # Exit code is MASKED
  echo "Result: $result"           # Runs even if command failed!
}

Even with set -e, the script will NOT exit because local returns 0:

set -e
my_function() {
  local output=$(false)  # false returns 1, but local returns 0
  echo "This runs!"      # Still executes
}
my_function

The Fix

Declare and assign on separate lines:

my_function() {
  local result
  result=$(failing_command)  # Exit code is preserved
  echo "Result: $result"     # Only runs on success (with set -e)
}

Same Issue with export and declare

# BAD: exit code masked
export PATH=$(build_path)
declare -r CONFIG=$(load_config)

# GOOD: separate declaration and assignment
export PATH
PATH=$(build_path)

declare -r CONFIG
CONFIG=$(load_config)

When It Doesn't Matter

If the command cannot fail, or you don't care about its exit status, combining is acceptable (though the linter will still flag it):

local timestamp=$(date +%s)  # date rarely fails
local hostname=$(hostname)   # also unlikely to fail

Best Practice

Always separate declaration and assignment in functions. It costs nothing and prevents a class of hard-to-debug issues where failures are silently ignored.