===== Personal guidelines for sh scripting =====

  * 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 ((i=0; i<3; i++))''
  * 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 ''$((${i}+1))'' 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**

<code sh>
var="$foo"
var="$foo$bar"
var="/path/$foo.suffix"
</code>

**Good**

<code sh>
var="${foo}"
var="${foo}${bar}"
var="/path/${foo}.suffix"
</code>

  * Define functions with an underscore prefix, eg,

**Bad**

<code sh>
encode64()
{
    steps
}
</code>

**Good**

<code sh>
_encode64()
{
  steps
}
</code>

  * Prefer minimal style:

**Bad**

<code sh>
if foo
then
    bar
fi

if [ -z "${foo}" ]; then
    cmd
fi

if [ -z "${foo}" ]; then
    cmd
else
    other_cmd
fi

_function()
{
    steps
}
</code>

**Good**

<code sh>
if foo; then
    bar
fi

[ -z "${foo}" ] && cmd

[ -z "${foo}" ] && cmd || other_cmd

_function() {
    steps
}
</code>

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

**Bad**

<code sh>
_foo()
{
    local first_argument="${1}"
}
</code>

**Good**

<code sh>
_foo()
{
    _foo__first_argument="${1}"
}
</code>

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

**Bad**

<code sh>
foo=bar
bar=${foo}
</code>

**Good**

<code sh>
foo="bar"
bar="${foo}"
</code>

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

**Bad**

<code sh>
echo "${foo}"
</code>

**Good**

<code sh>
printf "%s\\n" "${foo}"
</code>

  * Avoid fixed paths in commands:

**Bad**

<code sh>
[ -f /usr/bin/ps ] && /usr/bin/ps
</code>

**Good**

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

**Better**

<code sh>
[ -f "$(command -v "ps")" ] && $(command -v "ps")
</code>

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

**Bad**

<code sh>
ls | grep -qs file && return 0
</code>

**Good**

<code sh>
ls | grep file >/dev/null && return 0
</code>

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

**Bad**

<code sh>
ls > /tmp/ls.output
cat /tmp/ls.output && rm /tmp/ls.output
</code>

**Good**

<code sh>
ls_output="$(ls)"
printf "%s\\n" "${ls_output}"
</code>

**Better**

<code sh>
printf "%s\\n" "$(ls)"
</code>

  * On string comparations use X as a prefix

**Bad**

<code sh>
[ "${cmd}" = "foo" ] && cmd
</code>

**Good**
<code sh>
[ X"${cmd}" = X"foo" ] && cmd
</code>

  * Use ''||'' and ''&&'' over ''-a'' and ''-o''

**Bad**

<code sh>
if [ "-d" = "${1}" -o "--delete" = "${1}" ]; then
    foo
fi
</code>

**Good**

<code sh>
if [ X"-d" = X"${1}" ] || [ X"--delete" = "${1}" ]; then
    foo
fi
</code>