fish - 在 Fish shell 中测试字符串相等/字符串比较？

Question

你如何比较 Fish"abc" == "def"中的两个字符串（就像其他语言一样）？

到目前为止，我已经使用了contains（结果contains "" $a只返回0if$a是空字符串，尽管这似乎并不是在所有情况下对我都有效）和switch（使用 acase "what_i_want_to_match"和 a case '*'）的组合。不过，这些方法似乎都不是特别……正确。

Answer 1

  if [ "abc" != "def" ] 
        echo "not equal"
  end
  not equal

  if [ "abc" = "def" ]
        echo "equal"
  end

  if [ "abc" = "abc" ]
        echo "equal"
  end
  equal

或一个班轮：

if [ "abc" = "abc" ]; echo "equal"; end
equal

Answer 2

手册test有一些有用的信息。它与man test.

Operators for text strings
   o STRING1 = STRING2 returns true if the strings STRING1 and STRING2 are identical.

   o STRING1 != STRING2 returns true if the strings STRING1 and STRING2 are not
     identical.

   o -n STRING returns true if the length of STRING is non-zero.

   o -z STRING returns true if the length of STRING is zero.

例如

set var foo

test "$var" = "foo" && echo equal

if test "$var" = "foo"
  echo equal
end

您也可以使用[and]代替test.

这是检查空字符串或未定义变量的方法，这些在fish中是错误的。

set hello "world"
set empty_string ""
set undefined_var  # Expands to empty string

if [ "$hello" ]
  echo "not empty"  # <== true
else
  echo "empty"
end

if [ "$empty_string" ]
  echo "not empty"
else
  echo "empty"  # <== true
end

if [ "$undefined_var" ]
  echo "not empty"
else
  echo "empty"  # <== true
end