整理中…

printf

printf "0x%0x\n" 255

输出

0xff

test

s="hi"
test "$s" = "hi"
echo $?

[ "$s" = "hi" ]
echo $?

输出

0
0

if

if command
then
    commands if condition true
else
    commands if condition false
fi

if command 检测的是命令的退出码$?是否为0

if ls; then
    echo "ls ok"
else
    echo "ls not ok"
fi

if test ls; then
    echo "ls ok"
else
    echo "ls not ok"
fi

if [ ls ]; then
    echo "ls ok"
else
    echo "ls not ok"
fi

输出

ls ok
ls ok
ls ok

s="c"
if [ $s = "a" ]; then
    echo $s
elif [ $s = "b" ]; then
    echo $s
else
    echo "unknow"
fi

输出

unknow

for

for ((i = 0; i < 3; i++)) {
    echo -n "$i "
}
echo ""

for i in 0 1 2; do 
    echo -n "$i " 
done
echo ""

输出

0 1 2 
0 1 2

while

i=0
while [ $i -lt 3 ]; do 
    echo -n "$i "
    i=`expr $i + 1`
done 
echo ""

i=0
while [ $i -lt 3 ]; do 
    echo -n "$i "
    ((i++))
done 
echo ""

输出

0 1 2 
0 1 2

IFS

分割符

s="/usr/local/bin:/usr/bin:/bin"
for p in $s; do
    echo $p
done

echo ""

IFS=:
for p in $s; do
    echo $p
done

输出

/usr/local/bin:/usr/bin:/bin

/usr/local/bin
/usr/bin
/bin