什么是运营商QUOT之间的差异; = QUOT;和＆QUOT; ==＆QUOT;在Bash的？
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 ==?
答
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