什么是运营商QUOT之间的差异; = QUOT;和＆QUOT; ==＆QUOT;在Bash的？ [英] What is the difference between operator "=" and "==" in Bash?

问题描述

看来，这两个运营商pretty大同小异 - 是有区别吗？什么时候应该使用 = 当 == ？

It seems that these two operators are pretty much the same - is there a difference? When should I use = and when ==?

推荐答案

您必须使用 == 在数字比较中（（... ））：

You must use == in numeric comparisons in (( ... )):

$ if (( 3 == 3 )); then echo "yes"; fi
yes
$ if (( 3 = 3 ));  then echo "yes"; fi
bash: ((: 3 = 3 : attempted assignment to non-variable (error token is "= 3 ")

您可使用在字符串比较[[...]] 或 [...] 或测试：

$ if [[ 3 == 3 ]]; then echo "yes"; fi
yes
$ if [[ 3 = 3 ]]; then echo "yes"; fi
yes
$ if [ 3 == 3 ]; then echo "yes"; fi
yes
$ if [ 3 = 3 ]; then echo "yes"; fi
yes
$ if test 3 == 3; then echo "yes"; fi
yes
$ if test 3 = 3; then echo "yes"; fi
yes

字符串比较？，你说呢？

"String comparisons?", you say?

$ if [[ 10 < 2 ]]; then echo "yes"; fi    # string comparison
yes
$ if (( 10 < 2 )); then echo "yes"; else echo "no"; fi    # numeric comparison
no
$ if [[ 10 -lt 2 ]]; then echo "yes"; else echo "no"; fi  # numeric comparison
no

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