Shell Style Guide

#!SHEBANG

CONFIGURATION_VARIABLES

FUNCTION_DEFINITIONS

MAIN_CODE

#!/bin/bash
echo

#!/bin/sh
echo

set autoindent
set smartindent     "indent when
set tabstop=4       "tab width
set softtabstop=4   "backspace
set shiftwidth=4    "indent width
set expandtab       "expand tab to space
set shiftround

# DO use 'here document's
cat <<END;
I am an exceptionally long
string.
END

# Embedded newlines are ok too
long_string="I am an exceptionally
  long string."

# Single function
function my_func()
{
    ...
}

for zone in ${zones}; do
    something_with "${zone}"
done

# Constant
readonly PATH_TO_FILES='/some/path'

# Both constant and environment
declare -xr BACKUP_SID='PROD'

VERBOSE='false'
while getopts 'v' flag; do
  case "${flag}" in
    v) VERBOSE='true' ;;
  esac
done
readonly VERBOSE

zip_version="$(dpkg --status zip | grep Version: | cut -d ' ' -f 2)"
if [[ -z "${zip_version}" ]]; then
    error_message
else
    readonly zip_version
fi

my_func2()
{
    local name="$1"
    # 命令替换赋值，变量声明和赋值需放到不同行:
    local my_var
    my_var="$(my_func)" || return
    ...
}

my_func2() {
    # 禁止以下写法: $? 将获取到'local'指令的返回值, 而非 my_func
    local my_var="$(my_func)"
    [[ $? -eq 0 ]] || return

    ...
}

main()
{
    # 缩进4个空格
    say="hello"
    flag=0
    if [[ $flag = 0 ]]; then
        # 缩进4个空格
        echo "$say"
    fi
}

# 单行管道连接，管道左右空格
command1 | command2

# 长命令管道换行连接，管道放置于下一个命令开头，缩进4个空格
command1 
    | command2 
    | command3 
    | command4

# 管道左右无空格
command1|command2

# 换行连接管道放置于行末
command1 | 
    command2 | 
    command3 | 
    command4

echo "aaa2bccc" | grep -Eo "2|b"

echo "aaa2bccc" | grep -Eo "2 | b"

function clean_up()
{
    for dir in ${dirs_to_cleanup}; do
        if [ -d "${dir}/${BACKUP_SID}" ]; then
            log_date "Cleaning up old files in ${dir}/${BACKUP_SID}"
            rm "${dir}/${BACKUP_SID}/"*
            if [ "$?" -ne 0 ]; then
                error_message
            fi
        else
            mkdir -p "${dir}/${BACKUP_SID}"
            if [ "$?" -ne 0 ]; then
                error_message
            fi
        fi
    done
}

function getBatchName()
{
batch_name="batch"
if [[ "$input5"x == *$batch_name* ]]
then
batch_name=$input5
else if [[ "$input6"x == *$batch_name* ]]
then
batch_name=$input6
else if [[ "$input7"x == *$batch_name* ]]
then
batch_name=$input7
fi
fi
fi
}

case "${expression}" in
    a)
        variable="..."
        some_command "${variable}" "${other_expr}" ...
        ;;
    absolute)
        actions="relative"
        another_command "${actions}" "${other_expr}" ...
        ;;
    *)
        error "Unexpected expression '${expression}'"
        ;;
esac

verbose='false'
aflag=''
bflag=''
files=''
while getopts 'abf:v' flag; do
    case "${flag}" in
        a) aflag='true' ;;
        b) bflag='true' ;;
        f) files="${OPTARG}" ;;
        v) verbose='true' ;;
        *) error "Unexpected option ${flag}" ;;
    esac
done

main "$@"

#!/bin/bash
#
# Perform hot backups of databases.

#!/bin/bash
#
# Perform hot backups of databases.

export PATH='/usr/sbin/bin:/usr/bin:/usr/local/bin'

#######################################
# Cleanup files from the backup dir
# Globals:
#   BACKUP_DIR
#   BACKUP_SID
# Arguments:
#   None
# Returns:
#   None
#######################################
cleanup() {
    ...
}

# TODO(mrmonkey): Handle the unlikely edge cases (bug ####)
# TODO(--bug=123456): remove the "Last visitors" feature

function err() {
    echo "[$(date +'%FT%T%z')]: $@" >&2
}

if ! do_something; then
    err "Unable to do_something"
    exit "${E_DID_NOTHING}"
fi

# 位置变量和特殊变量，可以不用大括号:
echo "Positional: $1" "$5" "$3"
# $! 最后运行的后台Process的PID
# $- 使用Set命令设定的Flag一览
# $_ 在前台执行的前一个命令的最后一个参数
echo "Specials: !=$!, -=$-, _=$_. ?=$?, #=$# *=$* @=$@ $=$$ ..."

# 当位置变量大于等于10，则必须有大括号:
echo "many parameters: ${10}"

# 当出现歧义时，必须有大括号:
# Output is "a0b0c0"
set -- a b c
echo "${1}0${2}0${3}0"

# 使用变量扩展赋值时，必须有大括号：
DEFAULT_MEM=${DEFUALT_MEM:-"-Xms2g -Xmx2g -XX:MaxDirectMemorySize=4g"}

# 其他常规变量的推荐处理方式:
echo "PATH=${PATH}, PWD=${PWD}, mine=${some_var}"
while read f; do
    echo "file=${f}"
done < <(ls -l /tmp)
反例：

# 无引号, 无大括号, 特殊变量，单字符变量
echo a=$avar "b=$bvar" "PID=${$}" "${1}"

# 无大括号产生歧义场景：以下会被解析为 "${1}0${2}0${3}0",
# 而非 "${10}${20}${30}
set -- a b c
echo "$10$20$30"

# '单引号' 表示禁用变量替换
# "双引号" 表示需要变量替换

# 示例1： 命令替换需使用双引号
flag="$(some_command and its args "$@" 'quoted separately')"

# 示例2：常规变量需使用双引号
echo "${flag}"

# 示例3：整数不使用引号
value=32
# 示例4：即便命令替换输出为整数，也需要使用引号
number="$(generate_number)"

# 示例5：单词可以使用引号，但不作强制要求
readonly USE_INTEGER='true'

# 示例6：输出特殊符号使用单引号或转义
echo 'Hello stranger, and well met. Earn lots of $$$'
echo "Process $$: Done making $$$."

# 示例7：命令参数及路径不需要引号
grep -li Hugo /dev/null "$1"

# 示例8：常规变量用双引号，ccs可能为空的特殊情况可不用引号
git send-email --to "${reviewers}" ${ccs:+"--cc" "${ccs}"}

# 示例9：正则用单引号，$1可能为空的特殊情况可不用引号
grep -cP '([Ss]pecial||?characters*)$' ${1:+"$1"}

# 示例10：位置参数传递推荐带引号的"$@"，所有参数作为单字符串传递用带引号的"$*"
# content of t.sh
func_t() {
    echo num: $#
    echo args: 1:$1 2:$2 3:$3
}

func_t "$@"
func_t "$*"
# 当执行 ./t.sh a b c 时输出如下：
num: 3
args: 1:a 2:b 3:c
num: 1
args: 1:a b c 2: 3:

# 示例11：如果解析变量作为一个列表，则不能使用引号
list="one two three"

# you MUST NOT quote $list here
for word in $list; do
  ...
done

var="$(command "$(command1)")"

var="`command `command1``"  

# 示例1：正则匹配，注意右侧没有引号
# 详尽细节参考：http://tiswww.case.edu/php/chet/bash/FAQ 中E14部分
if [[ "filename" =~ ^[[:alnum:]]+name ]]; then
    echo "Match"
fi

# 示例2：严格匹配字符串"f*"(本例为不匹配)
if [[ "filename" == "f*" ]]; then
    echo "Match"
fi

# 示例3：[]中右侧不加引号将出现路径扩展，如果当前目录下有f开头的多个文件将报错[: too many arguments
if [ "filename" == f* ]; then
    echo "Match"
fi

if [[ "${my_var}" = "some_string" ]]; then
    do_something
fi

if [[ "${my_var}X" = "some_stringX" ]]; then
    do_something
fi

# 使用-z测试字符串为空
if [[ -z "${my_var}" ]]; then
    do_something
fi

# 使用空引号测试空字符串，能用但不推荐
if [[ "${my_var}" = "" ]]; then
    do_something
fi

# 使用-n测试非空字符串
if [[ -n "${my_var}" ]]; then
    do_something
fi

# 测试字符串非空，能用但不推荐
if [[ "${my_var}" ]]; then
    do_something
fi

# 例如目录下有以下4个文件和子目录：
# -f  -r  somedir  somefile

# 未指定路径的通配符扩展会把-r和-f当作rm的参数，强制删除文件：
psa@bilby$ rm -v *
removed directory: `somedir'
removed `somefile'

# 而指定了路径的则不会:
psa@bilby$ rm -v ./*
removed `./-f'
removed `./-r'
rm: cannot remove `./somedir': Is a directory
removed `./somefile'

# 以下设置的内容及成功与否并不明确
eval $(set_my_variables)

last_line='NULL'
your_command | while read line; do
    last_line="${line}"
done

# 以下会输出'NULL'：
echo "${last_line}"

total=0
# 仅当返回结果中无空格等特殊符号时以下可正常执行：
for value in $(command); do
    total+="${value}"
done

total=0
last_file=
# 注意两个<之间有空格，第一个为重定向，第二个<()为进程替换
while read count filename; do
    total+="${count}"
    last_file="${filename}"
done < <(your_command | uniq -c)

echo "Total = ${total}"
echo "Last one = ${last_file}"

# 使用if语句判断执行结果
if ! mv "${file_list}" "${dest_dir}/" ; then
    echo "Unable to move ${file_list} to ${dest_dir}" >&2
    exit "${E_BAD_MOVE}"
fi

# 或者使用$?
mv "${file_list}" "${dest_dir}/"
if [[ $? -ne 0 ]]; then
    echo "Unable to move ${file_list} to ${dest_dir}" >&2
    exit "${E_BAD_MOVE}"
fi

# 使用内建的算术扩展
addition=$((${X} + ${Y}))
# 使用内建的字符串替换
substitution="${string/#foo/bar}"

# 调用外部命令进行简单的计算
addition="$(expr ${X} + ${Y})"
# 调用外部命令进行简单的字符串替换
substitution="$(echo "${string}" | sed -e 's/^foo/bar/')"

source my_libs.sh

. my_libs.sh

grep net.ipv4 /etc/sysctl.conf
grep -c net.ipv4 /etc/sysctl.conf
wc -l /etc/sysctl.conf

cat /etc/sysctl.conf | grep net.ipv4
grep net.ipv4 /etc/sysctl.conf | wc -l
cat /etc/sysctl.conf | wc -l

# 当函数返回后可以继续执行cleanup
my_func() {
    [[ -e /dummy ]] || return 1
}

cleanup() {
    ...
}

my_func
cleanup

# 当函数退出时，cleanup将不会被执行
my_func() {
    [[ -e /dummy ]] || exit 1
}

cleanup() {
    ...
}

my_func
cleanup