4 SC1102

lacygoill edited this page 2022-09-26 19:33:14 +02:00

Table of Contents

• Shells disambiguate $(( differently or not at all. For $(command substitution), add space after $( . For $((arithmetics)), fix parsing errors.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:

Shells disambiguate $(( differently or not at all. For $(command substitution), add space after $( . For $((arithmetics)), fix parsing errors.

Problematic code:

echo "$((cmd "$@") 2>&1)"

Correct code:

echo "$( (cmd "$@") 2>&1)"

Rationale:

You appear to be using $(( with two (or more) parentheses in a row, where the first $( should open a subshell.

This is an ill-defined structure that is parsed differently between different shells and shell versions. Prefer adding spaces to make it unambiguous, both to shells and humans.

Consider the $((( in $(((1)) ):

Ash, dash and Bash 1 parses it as $(( ( and subsequently fail to find the matching )). Zsh and Bash 2+ looks ahead and parses it as $( ((. Ksh parses it as $( ( (.

Exceptions:

Alternatively, you may indeed have correctly spaced your parentheses, but ShellCheck failed to parse $(( as an arithmetic expression while accidentally succeeding in parsing it as $( + (.

In these cases, double check the syntax to ensure ShellCheck can parse the $((, or ignore this error and hope that it won't affect analysis too severely.

ShellCheck

• Installation

  • CentOS6
  • More Installation Guides

• Usage

  • Directive
  • Ignore

• Integrating and extending

  • Misc. contributions
  • Azure Pipelines
  • Buildkite
  • CircleCI
  • DevGuide
  • Integration
  • JUnit
  • Phabricator
  • TravisCI
  • GitLab CI
  • Drone
  • GitHub Actions

• Severity

• Template

Each individual ShellCheck warning has its own wiki page like SC1000. Use GitHub Wiki's "Pages" feature above to find a specific one, or see Checks.