5 SC3021

Joachim Ansorg edited this page 2022-10-31 15:31:21 +01:00

Table of Contents

• In POSIX sh, >& filename (as opposed to >& fd) is undefined.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Related resources:

In POSIX sh, >& filename (as opposed to >& fd) is undefined.

Note: ShellCheck 0.8.0 and below would trigger this warning on the perfectly POSIX compatible construct >& fd. If you are using >& to copy an integer file descriptor, please ignore this warning.

Problematic code:

# Writing to a filename
mycommand >& log.txt

Correct code:

mycommand > log.txt 2>&1

The following construct is also fine, as it uses an integer file descriptor instead of a filename:

fd=3
mycommand >& $fd

Rationale:

There are two forms of the >& file descriptor operator:

• >& integer such as >& 3 is a POSIX compatible synonym for 1>&3
• >& filename such as >& log.txt is a Bash specific synonym for > log.txt 2>&1

If (and only if) you are using the latter form, write it out as shown in the correct example to ensure portability.

Exceptions:

ShellCheck 0.8.0 and below incorrectly emits this warning for constructs like >& $var, even though this would be POSIX compatible when $var is an integer. In such cases, please ignore this warning.

Related resources:

• Shellcheck issue #2520
• Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!

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.