Compatibility

• Don't use syntax or semantics that are unique to the Bash shell. For example, the use of array constructs.
• Only use the POSIX subset - for example, use $(foo) over `foo`.
• You can check your scripts with 'sh -n' and 'checkbashisms'

Indenting

• Always use tabs over spaces.

Wrapping

• Generally, lines are 80 chars at maximum.
• Use the "Linux style" of line breaks:

  # Bad:
  if foo; then
      bar
  fi

  # Good:
  if foo
  then
      bar
  fi

• The same holds for functions:

  #Bad:
  foo () {
      bar
  }

  #Good:
  foo ()
  {
      bar
  }

Variables

• Variables are always in capital letters.
• Use braces around variables; eg. write ${FOO} instead of $FOO.
• Always protect variables with respect to potential whitespaces, write "${FOO}" not ${FOO}.
• For consistency reasons, always use quotes when assigning values to variables:

  #Bad:
  FOO=bar

  #Good:
  FOO="bar"

• If multiple variables are used, quote the full expression:

  #Bad:
  if [ -f "${FOO}"/foo/"${BAR}"/bar ]
  then
      foobar
  fi

  #Good:
  if [ -f "${FOO}/foo/${BAR}/bar" ]
  then
      foobar
  fi

Miscellaneous

• Use | as a separator in calls to sed, e.g. sed -e 's|foo|bar|'.
• Don't use the test command for comparisons or tests, use [ ], e.g. if [ -x /bin/foo ]; ... and not if test -x /bin/foo; ....