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兩個文件節點號都為262154，是硬鏈接

創建硬鏈接

兩個文件直接進行比較

-w判斷文件是否有寫權限

-e?判斷語句

shell按文件類型判斷

```sh

eric@rpi4b:~ $ ls -ali | grep test

?24553 -rw-r--r--? 1 eric eric ? 411? 9月 21 11:37 nvm_echo_test.sh

?30221 -rwxr-xr-x? 1 eric eric ? 172? 9月 21 18:03 shell-env-variable-test.sh

?24592 -rwxr-xr-x? 2 eric eric ? 156? 9月 21 13:15 test-hard-link.sh

?24592 -rwxr-xr-x? 2 eric eric ? 156? 9月 21 13:15 test.sh

?23662 lrwxrwxrwx? 1 eric eric ? ? 7 10月? 8 16:44 test-soft-link.sh -> test.sh

eric@rpi4b:~ $?

```

if [ 條件=??? ] then;
elif?[ 條件=??? ]?
else
fi

if then elif else if

bug ?

腳本名稱不要包含 grep 抓取的關鍵字 ?

端口 80 檢測

service httpd start ?RedHat 專用命令

/etc/rc.d/init.d/httpd start ? 通用方式，訪問文件的絕對路徑

&>/dev/null

輸出所有 log 信息到`空設備`文件，即丟棄所有的 log 信息

-n

apache

自動重啟

ps aux | grep httpd

進程 process

function read_test() {

?read -t 30 -p "input message: " var

?echo $var

}

read_test

abc

$??man?test?>?man-docs/test.md

pi@rpi3b:~/Desktop?$?cat?man-docs/test.md

cat?man-docs/test.md
TEST(1)???????????????????????????????????????????User?Commands??????????????????????????????????????????TEST(1)

NAME
???????test?-?check?file?types?and?compare?values

SYNOPSIS
???????test?EXPRESSION
???????test
???????[?EXPRESSION?]
???????[?]
???????[?OPTION

DESCRIPTION
???????Exit?with?the?status?determined?by?EXPRESSION.

???????--help?display?this?help?and?exit

???????--version
??????????????output?version?information?and?exit

???????An??omitted??EXPRESSION??defaults?to?false.??Otherwise,?EXPRESSION?is?true?or?false?and?sets?exit?status.
???????It?is?one?of:

???????(?EXPRESSION?)
??????????????EXPRESSION?is?true

???????!?EXPRESSION
??????????????EXPRESSION?is?false

???????EXPRESSION1?-a?EXPRESSION2
??????????????both?EXPRESSION1?and?EXPRESSION2?are?true

???????EXPRESSION1?-o?EXPRESSION2
??????????????either?EXPRESSION1?or?EXPRESSION2?is?true

???????-n?STRING
??????????????the?length?of?STRING?is?nonzero

???????STRING?equivalent?to?-n?STRING

???????-z?STRING
??????????????the?length?of?STRING?is?zero

???????STRING1?=?STRING2
??????????????the?strings?are?equal

???????STRING1?!=?STRING2
??????????????the?strings?are?not?equal

???????INTEGER1?-eq?INTEGER2
??????????????INTEGER1?is?equal?to?INTEGER2

???????INTEGER1?-ge?INTEGER2
??????????????INTEGER1?is?greater?than?or?equal?to?INTEGER2

???????INTEGER1?-gt?INTEGER2
??????????????INTEGER1?is?greater?than?INTEGER2

???????INTEGER1?-le?INTEGER2
??????????????INTEGER1?is?less?than?or?equal?to?INTEGER2

???????INTEGER1?-lt?INTEGER2
??????????????INTEGER1?is?less?than?INTEGER2

???????INTEGER1?-ne?INTEGER2
??????????????INTEGER1?is?not?equal?to?INTEGER2

???????FILE1?-ef?FILE2
??????????????FILE1?and?FILE2?have?the?same?device?and?inode?numbers

???????FILE1?-nt?FILE2
??????????????FILE1?is?newer?(modification?date)?than?FILE2

???????FILE1?-ot?FILE2
??????????????FILE1?is?older?than?FILE2

???????-b?FILE
??????????????FILE?exists?and?is?block?special

???????-c?FILE
??????????????FILE?exists?and?is?character?special

???????-d?FILE
??????????????FILE?exists?and?is?a?directory

???????-e?FILE
??????????????FILE?exists

???????-f?FILE
??????????????FILE?exists?and?is?a?regular?file

???????-g?FILE
??????????????FILE?exists?and?is?set-group-ID

???????-G?FILE
??????????????FILE?exists?and?is?owned?by?the?effective?group?ID

???????-h?FILE
??????????????FILE?exists?and?is?a?symbolic?link?(same?as?-L)

???????-k?FILE
??????????????FILE?exists?and?has?its?sticky?bit?set

???????-L?FILE
??????????????FILE?exists?and?is?a?symbolic?link?(same?as?-h)

???????-N?FILE
??????????????FILE?exists?and?has?been?modified?since?it?was?last?read

???????-O?FILE
??????????????FILE?exists?and?is?owned?by?the?effective?user?ID

???????-p?FILE
??????????????FILE?exists?and?is?a?named?pipe

???????-r?FILE
??????????????FILE?exists?and?read?permission?is?granted

???????-s?FILE
??????????????FILE?exists?and?has?a?size?greater?than?zero

???????-S?FILE
??????????????FILE?exists?and?is?a?socket

???????-t?FD??file?descriptor?FD?is?opened?on?a?terminal

???????-u?FILE
??????????????FILE?exists?and?its?set-user-ID?bit?is?set

???????-w?FILE
??????????????FILE?exists?and?write?permission?is?granted

???????-x?FILE
??????????????FILE?exists?and?execute?(or?search)?permission?is?granted

???????Except?for?-h?and?-L,?all?FILE-related?tests?dereference?symbolic?links.??Beware?that?parentheses?need?to
???????be??escaped??(e.g.,??by??backslashes)??for?shells.??INTEGER?may?also?be?-l?STRING,?which?evaluates?to?the
???????length?of?STRING.

???????NOTE:?Binary?-a?and?-o?are?inherently?ambiguous.??Use?'test?EXPR1?&&?test?EXPR2'?or?'test?EXPR1??||??test
???????EXPR2'?instead.

???????NOTE:??[??honors??the??--help??and?--version?options,?but?test?does?not.??test?treats?each?of?those?as?it
???????treats?any?other?nonempty?STRING.

???????NOTE:?your?shell?may?have?its?own?version?of?test?and/or?[,?which??usually??supersedes??the??version??de‐
???????scribed?here.??Please?refer?to?your?shell's?documentation?for?details?about?the?options?it?supports.

AUTHOR
???????Written?by?Kevin?Braunsdorf?and?Matthew?Bradburn.

REPORTING?BUGS
???????GNU?coreutils?online?help:?<https://www.gnu.org/software/coreutils/>
???????Report?any?translation?bugs?to?<https://translationproject.org/team/>

COPYRIGHT
???????Copyright?????2020??Free??Software??Foundation,??Inc.???License??GPLv3+:??GNU??GPL??version??3??or??later
???????<https://gnu.org/licenses/gpl.html>.
???????This?is?free?software:?you?are?free?to?change?and?redistribute?it.??There?is?NO?WARRANTY,?to??the??extent
???????permitted?by?law.

SEE?ALSO
???????Full?documentation?<https://www.gnu.org/software/coreutils/[>
???????or?available?locally?via:?info?'(coreutils)?test?invocation'

GNU?coreutils?8.32???????????????????????????????September?2020??????????????????????????????????????????TEST(1)

ll

-bash: ll：未找到命令

shell alias ?

https://github.com/xgqfrms/linux-shell-script-programming/issues/3#issuecomment-1576929059

文件權限

$ echo $?