for循环
for var in list;
do
commands;#使用变量$var
done
example:
for i in {a..z}; do actions; done;
后者
for((i=0;i<10;i++))
{
commands;
}
while condition
do
commands;
done
until循环
example:
x=0;
until [ $x -eq 9 ];
do
let x++; echo $x;
done
if比较语句
if contions;
then
commands;
if
else if和else语句
if condition;
then
commands;
else if conditon;then
commands;
else
commands;
fi
简洁用法：
[ condition ] && action;
[ condition ] || action;
算数比较：
[ $var -eq 0 ]
[ $var -ne 0 ]
逻辑与和逻辑或
[ $var1 -ne 0 -a $var2 -gt 2 ]
[ $var1 -ne 0 -o $var2 -gt 2 ]
example:
#!/bin/bash
#filename:compare.sh
fpath="/etc/passwd"
if [ -e $fpath ]; then
echo file exits;
else
echo does not exists;
fi