如何从Linux shell脚本中解析YAML文件？

如果你知道你感兴趣的标签和你期望的YAML结构，那么用Bash编写一个简单的YAML解析器并不难。

在下面的例子中，解析器将一个结构化的YAML文件读入环境变量、一个数组和一个关联数组。

注意：这个解析器的复杂性与YAML文件的结构有关。 你需要为YAML文件中的每个结构化组件单独编写一个子程序。 高度结构化的YAML文件可能需要一个更复杂的方法，例如一个通用的递归解析器。

xmas.yaml文件。

# Xmas YAML example
 # Values
 pear-tree: partridge
 turtle-doves: 2.718
 french-hens: 3
 # Array
 calling-birds:
   - huey
   - dewey
   - louie
   - fred
 # Structure
 xmas-fifth-day:
   calling-birds: four
   french-hens: 3
   golden-rings: 5
   partridges:
     count: 1
     location: "a pear tree"
   turtle-doves: two
解析器使用mapfile将文件作为一个数组读入内存，然后循环浏览每个标签并创建环境变量。
pear-tree:, turtle-doves: and french-hens: end up as simple environment variables
calling-birds: becomes an array
The xmas-fifth-day: structure is represented as an associative array however you could encode these as environment variables if you are not using Bash 4.0 or later.
Comments and white space are ignored.
#!/bin/bash
# -------------------------------------------------------------------
# A simple parser for the xmas.yaml file
# -------------------------------------------------------------------
# xmas.yaml tags
#  #                        - Ignored
#                           - Blank lines are ignored
#  ---                      - Initialiser for days-of-xmas 
#   pear-tree: partridge    - a string
#   turtle-doves: 2.718     - a string, no float type in Bash
#   french-hens: 3          - a number
#   calling-birds:          - an array of strings
#     - huey                - calling-birds[0]
#     - dewey
#     - louie
#     - fred
#   xmas-fifth-day:         - an associative array
#     calling-birds: four   - a string
#     french-hens: 3        - a number
#     golden-rings: 5       - a number
#     partridges:           - changes the key to partridges.xxx
#       count: 1            - a number
#       location: "a pear tree" - a string
#     turtle-doves: two     - a string
# This requires the following routines
# ParseXMAS
#   parses #, ---, blank line
#   unexpected tag error
#   calls days-of-xmas
# days-of-xmas
#   parses pear-tree, turtle-doves, french-hens
#   calls calling-birds
#   calls xmas-fifth-day
# calling-birds
#   elements of the array
# xmas-fifth-day
#   parses calling-birds, french-hens, golden-rings, turtle-doves
#   calls partridges
# partridges
#   parses partridges.count, partridges.location
function ParseXMAS()
  # days-of-xmas
  #   parses pear-tree, turtle-doves, french-hens
  #   calls calling-birds
  #   calls xmas-fifth-day
  function days-of-xmas()
    unset PearTree TurtleDoves FrenchHens
    while [ $CURRENT_ROW -lt $ROWS ]
      LINE=( ${CONFIG[${CURRENT_ROW}]} )
      TAG=${LINE[0]}
      unset LINE[0]
      VALUE="${LINE[*]}"
      echo "  days-of-xmas[${CURRENT_ROW}] ${TAG}=${VALUE}"
      if [ "$TAG" = "pear-tree:" ]
        declare -g PearTree=$VALUE
      elif [ "$TAG" = "turtle-doves:" ]
        declare -g TurtleDoves=$VALUE
      elif [ "$TAG" = "french-hens:" ]
        declare -g FrenchHens=$VALUE
      elif [ "$TAG" = "calling-birds:" ]
        let CURRENT_ROW=$(($CURRENT_ROW + 1))
        calling-birds
        continue
      elif [ "$TAG" = "xmas-fifth-day:" ]
        let CURRENT_ROW=$(($CURRENT_ROW + 1))
        xmas-fifth-day
        continue
      elif [ -z "$TAG" ] || [ "$TAG" = "#" ]
        # Ignore comments and blank lines
        # time to bug out
        break
      let CURRENT_ROW=$(($CURRENT_ROW + 1))
  # calling-birds
  #   elements of the array
  function calling-birds()
    unset CallingBirds
    declare -ag CallingBirds
    while [ $CURRENT_ROW -lt $ROWS ]
      LINE=( ${CONFIG[${CURRENT_ROW}]} )
      TAG=${LINE[0]}
      unset LINE[0]
      VALUE="${LINE[*]}"
      echo "    calling-birds[${CURRENT_ROW}] ${TAG}=${VALUE}"
      if [ "$TAG" = "-" ]
        CallingBirds[${#CallingBirds[*]}]=$VALUE
      elif [ -z "$TAG" ] || [ "$TAG" = "#" ]
        # Ignore comments and blank lines
        # time to bug out
        break
      let CURRENT_ROW=$(($CURRENT_ROW + 1))
  # xmas-fifth-day
  #   parses calling-birds, french-hens, golden-rings, turtle-doves
  #   calls fifth-day-partridges
  function xmas-fifth-day()
    unset XmasFifthDay
    declare -Ag XmasFifthDay
    while [ $CURRENT_ROW -lt $ROWS ]
      LINE=( ${CONFIG[${CURRENT_ROW}]} )
      TAG=${LINE[0]}
      unset LINE[0]
      VALUE="${LINE[*]}"
      echo "    xmas-fifth-day[${CURRENT_ROW}] ${TAG}=${VALUE}"
      if [ "$TAG" = "calling-birds:" ]
        XmasFifthDay[CallingBirds]=$VALUE
      elif [ "$TAG" = "french-hens:" ]
        XmasFifthDay[FrenchHens]=$VALUE
      elif [ "$TAG" = "golden-rings:" ]
        XmasFifthDay[GOLDEN-RINGS]=$VALUE
      elif [ "$TAG" = "turtle-doves:" ]
        XmasFifthDay[TurtleDoves]=$VALUE
      elif [ "$TAG" = "partridges:" ]
        let CURRENT_ROW=$(($CURRENT_ROW + 1))
        partridges
        continue
      elif [ -z "$TAG" ] || [ "$TAG" = "#" ]
        # Ignore comments and blank lines
        # time to bug out
        break
      let CURRENT_ROW=$(($CURRENT_ROW + 1))
  function partridges()
    while [ $CURRENT_ROW -lt $ROWS ]
      LINE=( ${CONFIG[${CURRENT_ROW}]} )
      TAG=${LINE[0]}
      unset LINE[0]
      VALUE="${LINE[*]}"
      echo "      partridges[${CURRENT_ROW}] ${TAG}=${VALUE}"
      if [ "$TAG" = "count:" ]
        XmasFifthDay[PARTRIDGES.COUNT]=$VALUE
      elif [ "$TAG" = "location:" ]
        XmasFifthDay[PARTRIDGES.LOCATION]=$VALUE
      elif [ -z "$TAG" ] || [ "$TAG" = "#" ]
        # Ignore comments and blank lines
        # time to bug out
        break
      let CURRENT_ROW=$(($CURRENT_ROW + 1))
  # ===================================================================
  # Load the configuration file
  mapfile CONFIG < xmas.yaml
  let ROWS=${#CONFIG[@]}
  let CURRENT_ROW=0
  # ---
  while [ $CURRENT_ROW -lt $ROWS ]
    LINE=( ${CONFIG[${CURRENT_ROW}]} )
    TAG=${LINE[0]}
    unset LINE[0]
    VALUE="${LINE[*]}"
    echo "[${CURRENT_ROW}] ${TAG}=${VALUE}"
    if [ "$TAG" = "---" ]
        let CURRENT_ROW=$(($CURRENT_ROW + 1))
        days-of-xmas
        continue
    elif [ -z "$TAG" ] || [ "$TAG" = "#" ]
        # Ignore comments and blank lines
        echo "Unexpected tag at line $(($CURRENT_ROW + 1)): <${TAG}>={${VALUE}}"
        break
    let CURRENT_ROW=$(($CURRENT_ROW + 1))
echo =========================================
ParseXMAS
echo =========================================
declare -p PearTree
declare -p TurtleDoves
declare -p FrenchHens
declare -p CallingBirds
declare -p XmasFifthDay
This produces the following output
=========================================
[0] #=Xmas YAML example
[1] ---=
  days-of-xmas[2] #=Values
  days-of-xmas[3] pear-tree:=partridge
  days-of-xmas[4] turtle-doves:=2.718
  days-of-xmas[5] french-hens:=3
  days-of-xmas[6] =
  days-of-xmas[7] #=Array
  days-of-xmas[8] calling-birds:=
    calling-birds[9] -=huey
    calling-birds[10] -=dewey
    calling-birds[11] -=louie
    calling-birds[12] -=fred
    calling-birds[13] =
    calling-birds[14] #=Structure
    calling-birds[15] xmas-fifth-day:=
  days-of-xmas[15] xmas-fifth-day:=
    xmas-fifth-day[16] calling-birds:=four
    xmas-fifth-day[17] french-hens:=3
    xmas-fifth-day[18] golden-rings:=5
    xmas-fifth-day[19] partridges:=
      partridges[20] count:=1
      partridges[21] location:="a pear tree"
      partridges[22] turtle-doves:=two
    xmas-fifth-day[22] turtle-doves:=two
=========================================
declare -- PearTree="partridge"
declare -- TurtleDoves="2.718"
declare -- FrenchHens="3"
declare -a CallingBirds=([0]="huey" [1]="dewey" [2]="louie" [3]="fred")
declare -A XmasFifthDay=([CallingBirds]="four" [PARTRIDGES.LOCATION]="\"a pear tree\"" [FrenchHens]="3" [GOLDEN-RINGS]="5" [PARTRIDGES.COUNT]="1" [TurtleDoves]="two" )