１，$$：显示当前的进程id号
[email protected]:~/linux/shell/how_to_use_var$ cat show_pid.sh #!/bin/bash echo $$ sleep 3000 [email protected]:~/linux/shell/how_to_use_var$ bash show_pid.sh & [1] 9401 [email protected]:~/linux/shell/how_to_use_var$ 9401 [email protected]:~/linux/shell/how_to_use_var$ ps -ef | grep show_pid ghostwu 9401 2792 0 06:07 pts/18 00:00:00 bash show_pid.sh ghostwu 9404 2792 0 06:07 pts/18 00:00:00 grep --color=auto show_pid
[email protected]:~/linux/shell/how_to_use_var$ ps -ef | grep show_pid | grep -v grep ghostwu 9401 2792 0 06:07 pts/18 00:00:00 bash show_pid.sh
[email protected]:~/linux/shell/how_to_use_var$ kill 9401 [email protected]:~/linux/shell/how_to_use_var$ ps -ef | grep show_pid ghostwu 9478 2792 0 06:08 pts/18 00:00:00 grep --color=auto show_pid [1]+ Terminated bash show_pid.sh
2，(())用于整数的常用运算符
>把两个整数的运算结果赋值给一个变量，前面要加$
[email protected]:~/linux/shell/how_to_use_var$ a=((10+20)) bash: syntax error near unexpected token `(‘ [email protected]:~/linux/shell/how_to_use_var$ a=$((10+20)) [email protected]:~/linux/shell/how_to_use_var$ echo $a 30
3，四则运算
[email protected]:~/linux/shell/how_to_use_var$ bash calc.sh 10 2 a+b=12 a-b=12 a*b=12 a/b=12 a**b=100 a%b=0 [email protected]:~/linux/shell/how_to_use_var$ cat calc.sh #!/bin/bash a=$1 b=$2 echo "a+b=$(($a+$b))" echo "a-b=$(($a+$b))" echo "a*b=$(($a+$b))" echo "a/b=$(($a+$b))" echo "a**b=$(($a**$b))" echo "a%b=$(($a%$b))"
4，let用于整数运算，类似(())
[email protected]:~/linux/shell/how_to_use_var$ i=10 [email protected]:~/linux/shell/how_to_use_var$ let i=i+10 [email protected]:~/linux/shell/how_to_use_var$ echo $i 20
不使用let，是不会计算变量的值
[email protected]:~/linux/shell/how_to_use_var$ i=2 [email protected]:~/linux/shell/how_to_use_var$ i=i+8 [email protected]:~/linux/shell/how_to_use_var$ echo $i i+8
5，bash内置命令read,通过参数-p 提示信息，读入变量的值
[email protected]:~/linux/std_err_out$ read -p "pls input 2 number:" a b pls input 2 number:10 20 [email protected]:~/linux/std_err_out$ echo $a $b 10 20
10，test -f 判断普通文件是否存在
[email protected]:~/linux/std_err_out$ ls ghostwu.txt output_error.txt std_out1.txt std_out.txt [email protected]:~/linux/std_err_out$ test -f ghostwu.txt && echo 1 || echo 0 1 [email protected]:~/linux/std_err_out$ test -f ghostwu2.txt && echo 1 || echo 0 0
test -z 测试字符串长度是否为0
gh[email protected]:~/linux/std_err_out$ test -z "hello" && echo 1 || echo 0 0 [email protected]:~/linux/std_err_out$ test -z "" && echo 1 || echo 0 1
中括号[]与test一样.
[email protected]:~/linux/std_err_out$ [ -f ghostwu.txt ] && echo 1 || echo 0 1 [email protected]:~/linux/std_err_out$ [ -f ghostwu2.txt ] && echo 1 || echo 0 0
11，判断一个变量值或者字符串是否为整数？
利用expr做计算时变量或者字符串必须是整数的规则，把一个变量或字符串和一个已知的整数（非0)相加，看命令返回的值是否为0。如果为0，就认为做加法的变量或字符串为整数，否则不是整数。
[email protected]:~/linux/shell/flow_control$ i=10 [email protected]:~/linux/shell/flow_control$ expr $i + 1 >/dev/null [email protected]:~/linux/shell/flow_control$ echo $? 0 [email protected]:~/linux/shell/flow_control$ i=‘a‘ [email protected]:~/linux/shell/flow_control$ expr $i + 1 >/dev/null 2>&1 [email protected]:~/linux/shell/flow_control$ echo $? 2
原文地址：https://www.cnblogs.com/ghostwu/p/9103185.html
时间： 2024-10-19 10:50:49