33.3. 测试和比较: 另一种方法

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2023-12-01

对于测试,[[ ]]结构可能比[]更合适.同样地,算术比较可能用(( ))结构更有用.

   1 a=8
   2
   3 # 下面所有的比较是等价的.
   4 test "$a" -lt 16 && echo "yes, $a < 16"         # "与列表"
   5 /bin/test "$a" -lt 16 && echo "yes, $a < 16"
   6 [ "$a" -lt 16 ] && echo "yes, $a < 16"
   7 [[ $a -lt 16 ]] && echo "yes, $a < 16"          # 在[[ ]]和(( ))中不必用引号引起变量
   8 (( a < 16 )) && echo "yes, $a < 16"             #
   9
  10 city="New York"
  11 # 同样，下面的所有比较都是等价的.
  12 test "$city" \< Paris && echo "Yes, Paris is greater than $city"  # 产生 ASCII 顺序.
  13 /bin/test "$city" \< Paris && echo "Yes, Paris is greater than $city"
  14 [ "$city" \< Paris ] && echo "Yes, Paris is greater than $city"
  15 [[ $city < Paris ]] && echo "Yes, Paris is greater than $city"    # 不需要用引号引起$city.
  16
  17 # 多谢, S.C.