方法一：使用字符串過濾出非0到9之間的字符。
[root@managevm1 ~]# a=123
[root@managevm1 ~]# echo $a | grep "[^0-9]" && echo "a isn't an integer" \
|| echo "a is an integer"
a is an integer
[root@managevm1 ~]# a=123.4
[root@managevm1 ~]# echo $a | grep "[^0-9]" && echo "a isn't an integer" \
|| echo "a is an integer"
a isn't an integer
也可以寫爲
[root@managevm1 ~]# echo $a | grep -v "[0-9]*" && echo "a isn't an integer"\
|| echo "a is an integer"
方法二：使用條件判斷，$a中0到9出現一次以上，且不包含其他字符。
[root@managevm1 ~]# a=123
[root@managevm1 ~]# if [[ $a =~ ^[0-9]\{1,\}$ ]]; then echo "a is an integer;"\
else echo "a is not an integer"; fi
a is an integer
[root@managevm1 ~]# a=123.4
[root@managevm1 ~]# if [[ $a =~ ^[0-9]\{1,\}$ ]]; then echo "a is an integer;"\
else echo "a is not an integer"; fi
a is not an integer
這個命令也可以簡單寫成
[root@managevm1 ~]# [[ $a =~ ^[0-9]*$ ]] && echo "a is an integer" || \
echo "a is not an integer"
方法三：awk過濾
[root@managevm1 ~]# echo $a|awk '/^[0-9]*$/{print "a is an integer"}'
a is an integer
或寫成
[root@managevm1 ~]# echo $a|awk '{if ($1~/^[0-9]*$/) print "a is an integer"}'
a is an integer
方法四:使用命令bc來計算，因爲shell不支持浮點預算，非整數a的值除1後會得到整數部分與原值不符合
注意這裏使用 == 是做字符串的比較非數值比較。數值比較用 -eq ， 不支持浮點。
[root@managevm1 ~]# a=123
[root@managevm1 ~]# [ $(echo $a/1|bc) == "$a" ] && echo "It's an integer" \
|| echo "It's not an integer"
It's an integer
[root@managevm1 ~]# a=123.4
[root@managevm1 ~]# [ $(echo $a/1|bc) == "$a" ] && echo "It's an integer" \
|| echo "It's not an integer"
It's not an integer
方法五：利用test下不支持浮點數比較的特性，通過命令的返回狀態來判斷。
[root@managevm1 ~]# a=123
[root@managevm1 ~]# [ $a -ge 0 ] 2>/dev/null && echo "A is an integer"|| \
echo "a is NOT an integer"
A is an integer
[root@managevm1 ~]# a=123.4
[root@managevm1 ~]# [ $a -ge 0 ] 2>/dev/null && echo "A is an integer"|| \
echo "a is NOT an integer"
a is NOT an integer
