• Avoid syntax or semantics unique to bash, zsh, or any other specific shell, eg:
  • array contructs
  • parameter subtitution; <() or >()
  • {a,b,c} or {1..10}
  • the function keyword at the beginning of a function
  • C-like for loops, for 1)
• Avoid basename, use expr or substrings (${variable##\*/}) instead
• Use = over ==
• Use case over test or [ for regex
• Use [ or test over [[
• Use command -v over which
• Use awk over sed, grep, cut, sort, tr or unique
• Use /bin/sh over /bin/bash or /usr/bin/env sh
• Use $(foo) over \foo\``
• Use $2) over $(expr “${i}” + 1)
• Use : as a sed separator, eg: sed -e 's:foo:bar:'
• Use lowercase over uppercase, except in vars users will interact with, eg: LC_ALL
• Use spaces over tabs
• Use braces around variables, eg,

Bad

var="$foo"
var="$foo$bar"
var="/path/$foo.suffix"

Good

var="${foo}"
var="${foo}${bar}"
var="/path/${foo}.suffix"

• Define functions with an underscore prefix, eg,

Bad

encode64()
{
    steps
}

Good

_encode64()
{
  steps
}

• Prefer minimal style:

Bad

if foo
then
    bar
fi
 
if [ -z "${foo}" ]; then
    cmd
fi
 
if [ -z "${foo}" ]; then
    cmd
else
    other_cmd
fi
 
_function()
{
    steps
}

Good

if foo; then
    bar
fi
 
[ -z "${foo}" ] && cmd
 
[ -z "${foo}" ] && cmd || other_cmd
 
_function() {
    steps
}

• Local variables should be named after their function name and separated by doble underscore, avoid local

Bad

_foo()
{
    local first_argument="${1}"
}

Good

_foo()
{
    _foo__first_argument="${1}"
}

• Use quotes when assigning values to variables, use single quotes when absolutely necesary

Bad

foo=bar
bar=${foo}

Good

foo="bar"
bar="${foo}"

• Use printf over echo (specially when echoing ${vars})

Bad

echo "${foo}"

Good

printf "%s\\n" "${foo}"

• Avoid fixed paths in commands:

Bad

[ -f /usr/bin/ps ] && /usr/bin/ps

Good

if command -v "ps" > /dev/null; then
    $(command -v "ps")
fi

Better

[ -f "$(command -v "ps")" ] && $(command -v "ps")

• Avoid -q in grep, send stdout to /dev/null instead

Bad

ls | grep -qs file && return 0

Good

ls | grep file >/dev/null && return 0

• Do NOT write to the file system, use vars or pipes instead

Bad

ls > /tmp/ls.output
cat /tmp/ls.output && rm /tmp/ls.output

Good

ls_output="$(ls)"
printf "%s\\n" "${ls_output}"

Better

printf "%s\\n" "$(ls)"

• On string comparations use X as a prefix

Bad

[ "${cmd}" = "foo" ] && cmd

Good

[ X"${cmd}" = X"foo" ] && cmd

• Use || and && over -a and -o

Bad

if [ "-d" = "${1}" -o "--delete" = "${1}" ]; then
    foo
fi

Good

if [ X"-d" = X"${1}" ] || [ X"--delete" = "${1}" ]; then
    foo
fi