学习shell编程（二）

视频地址：https://www.bilibili.com/video/av23774844/?p=12

typeset

#!/bin/bash
function f1 {
    typeset x
    x=7
    y=8
}
x=1
y=2
echo x is $x
echo y is $y
f1
echo x is $x
echo y is $y

declare

#!/bin/bash
declare -l lstring="ABCdef"
declare -u ustring="ABCdef"
declare -r readonly="A Value"
declare -a Myarray
declare -A Myarray2

echo lstring = $lstring
echo ustring = $ustring
echo readonly = $readonly
readonly="New Value"
Myarray[2]="Second Value"
echo 'Myarray[2]= ' ${Myarray[2]}
Myarray2["hotdog"]="baseball"
echo 'Myarray2[hotdog]= ' ${Myarray2["hotdog"]}

read

while

for

while.sh

#!/bin/bash
x=1
while
    ((x<10))
do
    echo loop $x
    date >date.$x
    ((x=x+1))
done

whie2.sh

#!/bin/bash
ls -l /etc | while
    read a b c d
do
    echo owner is $c
done

利用这种方法就可以整理出文件的拥有者

for.sh

#!/bin/bash
for i in dog cat hotdog
do
    echo i is $i
done

for i in `seq 3 5`
do
    echo i in seq is $i
done

for i in {N..P}
do
    echo i in letter list is $i
done

for d in $(<data_file)
do
    echo d in data_file is $d
done

for f in $(find /etc 2>/dev/null | grep grub)
do
    echo grub named things are $f
done

function

func.sh

#!/bin/bash
function myfunc {
    echo starting myfunc
    return
    echo this will not be executed
}

myfunc
n=$(myfunc)
echo n is $n

func2.sh

#!/bin/bash
function f2 {
    echo in f2
    exit 2
    echo more in f2
}
echo strarting
f2
echo after f2

视频地址：https://www.bilibili.com/video/av23774844/?p=15

重定向和管道

#!/bin/bash
echo Just '>' -----------------------------
find /etc -name grub >grub.out
echo Doing '2>' -----------------------------
find /etc -name grub 2>errs.out
echo Doing '&>' -----------------------------
find /etc -name grub &>both.out

#!/bin/bash
exec 19<data_file
lsof -p $$
cat 0<&19
exec 7>&1   #save stdout in 7
exec 7>&-   # close stdout
lsof -p $$
cat         # no stdout now
exec 1>&7   # copy 7 back to stdout
cat

case

#!/bin/bash
echo -n "Print message? "
valid=0
while
    [ $valid == 0 ]
do
    read ans
    case $ans in
        yes|YES|y|Y )   echo Will print the message
                        echo The Message
                        valid=1
                        ;;
        [nN][oN]    )   echo Will Not print the message
                        valid=1 ;;
        *           )   echo Yes or No of some form please ;;
    esac
done

if

#!/bin/bash
if test -x /bin/ls
then
    if
        [ ! -w /etc/hosts ]
    then
        if
            echo about to look for foobar
            grep -q foobar /etc/passwd
        then
            echo foobar found in /etc/passwd
        else
            echo foobar not found
        fi
    fi
else
    echo Oh no, /bin/ls not excutable
fi

test

#!/bin/bash
x=01
y=1
echo comparing $x and $y
if
    [ $x == $y ]
then
    echo ==
else
    echo not ==
fi
if
    [ $x -eq $y ]
then
    echo eq
else
    echo not eq
fi

if(( x==y ))
then
    echo '(())' ==
else
    echo not '(())' ==
fi

注意！
== 比较的是字符串
eq 比较的是数字

算术运算

#!/bin/bash
((n=2**3 + 5))  # 2的3次方
echo n = $n     # 13
((y=n^4))       # n(13)异或4
echo y = $y     # 9