bash中對hashmap的間接參考

我正在撰寫一個腳本來從 .deb 檔案安裝軟體包，但首先，我想檢查每個軟體包是否已安裝。我有一個組態檔，其中包含作為哈希圖的包資訊，如下所示：

declare -A package_a=(
[name]="utility-blah"
[ver]="1.2"
[arch]="amd64"
)
declare -A package_b=(
[name]="tool-bleh"
[ver]="3.4"
[arch]="all"
)
#and so on and so forth

我的安裝腳本來源組態檔，我希望它遍歷包，檢查它們是否已安裝，如果沒有安裝它們，如下所示：

source packages.config
declare -a packageList=("package_a" "package_b" "package_d")
for package in ${packageList[@]}; do
    # Check if the specific version is installed already
    if apt show ${package[name]}=${package[ver]}; then
        echo ${package[name]} ${package[ver]} is already installed.
    else
        echo Installing ${package[name]}
        sudo apt install path/to/files/${package[name]}_${package[ver]}_${package[arch]}.deb
    fi
done    

如何package指向包含有關包的資訊的哈希圖并在以下命令中使用它？

我在 Ubuntu 18.04 上使用 Bash 4.4.20

uj5u.com熱心網友回復：

使用 nameref 的一個想法：

source packages.config
declare -a packageList=("package_a" "package_b" "package_d")

for pkg in "${packageList[@]}"; do                                      # change variable name
    declare -n package="${pkg}"                                           # declare nameref; rest of code remains the same ...

    # Check if the specific version is installed already
    if apt show ${package[name]}=${package[ver]}; then
        echo ${package[name]} ${package[ver]} is already installed.
    else
        echo Installing ${package[name]}
        sudo apt install path/to/files/${package[name]}_${package[ver]}_${package[arch]}.deb
    fi
done  

或者（正如 M. Nejat Aydin 和 Benjamin W. 指出的那樣）declare -n可以在while回圈之前進行，例如：

declare -n package

for package in "${packageList[@]}"; do                                          
    # Check if the specific version is installed already
    if apt show ${package[name]}=${package[ver]}; then
        echo ${package[name]} ${package[ver]} is already installed.
    else
        echo Installing ${package[name]}
        sudo apt install path/to/files/${package[name]}_${package[ver]}_${package[arch]}.deb
    fi
done  

簡單測驗：

declare -n package

for package in ${packageList[@]}; do 
    echo "${!package} : ${package[name]}"
done

這會產生：

package_a : utility-blah
package_b : tool-bleh
package_d :

uj5u.com熱心網友回復：

這種輸入資料更適合 JSON，而不是使用 bash 關聯陣列和間接。

假設你有一個packages.json：

{
  "packages": [
    {
      "package": "package_a",
      "name": "utility-blah",
      "ver": "1.2",
      "arch": "amd64"
    },
    {
      "package": "package_b",
      "name": "utility-bleh",
      "ver": "3.4",
      "arch": "all"
    },
    {
      "package": "apache2",
      "name": "Apache2 http server",
      "ver": "2.4.52-1ubuntu4.1",
      "arch": "all"
    }
  ]
}

這樣簡單的 POSIX-shell 腳本能夠根據需要處理它：

#! /bin/sh

# Fields are tab-delimited, records end with newline
IFS=$(printf '\t')

# Parses json input into record lines
jq -r '.packages[]|(.package   "\t"   .name   "\t"   .ver)' packages.json |

  # Iterates records, reading fields
  while read -r package name ver; do
    {
      # Query package for installed status and version
      # formatted into two fields
      dpkg-query -W --showformat='${db:Status-Abbrev}\t${Version}' "${package}" || :
    } 2>/dev/null | {

      # Reads status and installed version
      read -r status installed_ver _

      # If status is installed 'ii ' and installed version matches'
      if [ "${status}x" = 'ii x' ] && [ "${ver}x" = "${installed_ver}x" ]; then
        printf '%s %s is already installed.\n' "${name}" "${ver}"
      else
        printf 'Installing %s.\n' "${name}"
      fi
    }
  done

示例輸出：

nstalling utility-blah.
nstalling utility-bleh.
Apache2 http server 2.4.52-1ubuntu4.1 is already installed.

標籤：重击ubuntu

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