This guideline is heavily inspired from the Debian Live Coding Style.

• 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'

• Always use tabs over spaces.

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

# Bad:
iffoo;then
bar
fi

# Good:
iffoo
then
bar
fi

• The same holds for functions:

#Bad:
foo(){
bar
}

#Good:
foo()
{
bar
}

• 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

• 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; ....