下面的代码似乎适用于我的用例:

例子

$ tern 1 YES NO                                                                             
YES
    
$ tern 0 YES NO                                                                             
NO
    
$ tern 52 YES NO                                                                            
YES
    
$ tern 52 YES NO 52                                                                         
NO

并且可以像这样在脚本中使用:

RESULT=$(tern 1 YES NO)
echo "The result is $RESULT"

tern

#!/usr/bin/env bash

function show_help()
{
  ME=$(basename "$0")
  IT=$(cat <<EOF

  Returns a ternary result

  usage: BOOLEAN VALUE_IF_TRUE VALUE_IF_FALSE
  
  e.g. 
  
  # YES
  $ME 1 YES NO                                

  # NO
  $ME 0 YES NO

  # NO
  $ME "" YES NO

  # YES
  $ME "STRING THAT ISNT BLANK OR 0" YES NO

  # INFO contains NO
  INFO=\$($ME 0 YES NO)
EOF
)
  echo "$IT"
  echo
  exit
}

if [ "$1" = "help" ] || [ "$1" = '?' ] || [ "$1" = "--help" ] || [ "$1" = "h" ]; then
  show_help
fi
if [ -z "$3" ]
then
  show_help
fi

# Set a default value for what is "false" -> 0
FALSE_VALUE=${4:-0}

function main
{
  if [ "$1" == "$FALSE_VALUE" ] || [ "$1" = '' ]; then
    echo $3
    exit;
  fi;

  echo $2
}

main "$1" "$2" "$3"

这是通解

也适用于字符串测试 感觉更像是一种表达 避免在条件失效时产生任何微妙的副作用

数值比较试验

a=$(if [ "$b" -eq 5 ]; then echo "$c"; else echo "$d"; fi)

字符串比较测试

a=$(if [ "$b" = "5" ]; then echo "$c"; else echo "$d"; fi)

三元运算符?:是if/else的缩写形式

case "$b" in
 5) a=$c ;;
 *) a=$d ;;
esac

Or

 [[ $b = 5 ]] && a="$c" || a="$d"

let命令支持大多数基本操作符:

let a=b==5?c:d;

当然，这只适用于分配变量;不能执行其他命令。

如果条件仅仅是检查是否设置了变量，甚至还有更短的形式:

a=${VAR:-20}

如果VAR已设置，则会将VAR值赋给a，否则将为其赋值默认值20——这也可以是表达式的结果。

这种方法在技术上称为“参数展开”。

下面的代码似乎适用于我的用例:

例子

$ tern 1 YES NO                                                                             
YES
    
$ tern 0 YES NO                                                                             
NO
    
$ tern 52 YES NO                                                                            
YES
    
$ tern 52 YES NO 52                                                                         
NO

并且可以像这样在脚本中使用:

RESULT=$(tern 1 YES NO)
echo "The result is $RESULT"

tern

#!/usr/bin/env bash

function show_help()
{
  ME=$(basename "$0")
  IT=$(cat <<EOF

  Returns a ternary result

  usage: BOOLEAN VALUE_IF_TRUE VALUE_IF_FALSE
  
  e.g. 
  
  # YES
  $ME 1 YES NO                                

  # NO
  $ME 0 YES NO

  # NO
  $ME "" YES NO

  # YES
  $ME "STRING THAT ISNT BLANK OR 0" YES NO

  # INFO contains NO
  INFO=\$($ME 0 YES NO)
EOF
)
  echo "$IT"
  echo
  exit
}

if [ "$1" = "help" ] || [ "$1" = '?' ] || [ "$1" = "--help" ] || [ "$1" = "h" ]; then
  show_help
fi
if [ -z "$3" ]
then
  show_help
fi

# Set a default value for what is "false" -> 0
FALSE_VALUE=${4:-0}

function main
{
  if [ "$1" == "$FALSE_VALUE" ] || [ "$1" = '' ]; then
    echo $3
    exit;
  fi;

  echo $2
}

main "$1" "$2" "$3"