STYLE.md

Style guideline

• 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 parameter expansion (${variable##*/}) instead

• Avoid parsing ls output

• Use = over ==

• Use case over test or [ for regex

• Use [ or test over [[

• Use command -v or type over which

• Use parameter expansion over awk,cut or basename on simple strings

• Use awk over sed, grep, cut, sort, tr or unique

• Use /bin/sh over /bin/bash or /usr/bin/env bash

• 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: GLOBAL_VAR_PROGRAM

• Use spaces over tabs

• Avoid forking or using extra pipes when not necessary, eg,

  Bad

  is_directory()
  {
     [ -d "${1}" ]
  }
  
  sed 's:foo:bar:g' | sed 's:more:less:g'
  if is_directory "${directory}"
     printf "%s\\n" "${directory} is a directory"
  fi

  Good

  sed 's:foo:bar:g;s:more:less:g'
  if [ -d "${directory}" ]
     printf "%s\\n" "${directory} is a directory"
  fi
  [ -d "${directory}" ] && printf "%s\\n" "${directory} is a directory"

• Use braces around multiple variables, eg,

  Bad

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

  Good

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

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

  Bad

  foo=bar
  bar=${foo}

  Good

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

• 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
  
  _foo()
  {
      _foo__first_argument="${1}"
      printf "%s\\n" "${_foo__first_argument}"
  }

  Good

  if foo; then
      bar
  fi
  
  [ -z "${foo}" ] && cmd
  
  [ -z "${foo}" ] && cmd || other_cmd
  
  _foo()
  {
      printf "%s\\n" "${1}"
  }

• Local variables should be named unique after their function name (or an abbreviation of it) and separated by doble underscore, avoid local

  Bad

  _foo()
  {
      local basename="${1##*/}"
  }
  
  _foo_bar()
  {
      local basename="${1##*/}"
  }

  Good

  _foo()
  {
      _foo__basename="${1##*/}"
  }
  
  _foo_bar()
  {
      _fbar__basename="${1##*/}"
  }

• 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 "mplayer")" ] && $(command -v "mplayer")

• Avoid -q in grep, git and other command, redirect stdout to /dev/null instead

  Bad

  grep -qs pattern file && return 0

  Good

  grep pattern file >/dev/null && return 0

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

  Bad

  grep pattern file > /tmp/grep.output

  Good

  grep_output="$(grep pattern file)"

• Use || and && over -a and -o

  Bad

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

  Good

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