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test

字串或文字的比對
Str1 = str2 | 當str1與str2相同時, 傳回True
Str1 != str2| 當str1與str2不同時, 傳回True
Str1 < Str2 
Str1 <= Str2
Str1 > Str2
Str1 >= Str2
Str     | 當str不是空字符時, 傳回True
-n str  | 當str的長度大於0時, 傳回True
-z str  | 當str的長度是0時, 傳回True
[ ]與[[ ]] 差別
    [ ... ] : POSIX 相容指令，別名 test，用於條件判斷式。 [[ ... ]] : Bash 專有語法，可用於更複雜的條件判斷式。 [ -n "$VAR_STR"] : 使用 [ ] 時要注意變數的雙引號用法

    範例：

    VAR_STR=""
if [[ -n $VAR_STR ]]; then
    echo "var str is nonzero with [["
else
    echo "var str is zero with [["
fi

if [ -n $VAR_STR ]; then
    echo "var str is nonzero with ["
else
    echo "var str is zero with ["
fi

    Output:

    var str is zero with [[
var str is nonzero with [

    Fix:

    VAR_STR=""

if [[ -n $VAR_STR ]]; then
    echo "var str is nonzero with [["
else
    echo "var str is zero with [["
fi

if [ -n "$VAR_STR" ]; then  # <<<<
    echo "var str is nonzero with ["
else
    echo "var str is zero with ["
fi
    數值型比對

    整數

    Int1 -eq int2 |當int1等於int2時, 傳回True
Int1 -ge int2 |當int1大於/等於int2時, 傳回True
Int1 -le int2 |當int1小於/等於int2時, 傳回True
Int1 -gt int2 |當int1大於int2時, 傳回True
Int1 -ne int2 |當int1不等於int2時, 傳回True
Int1 -lt int2 |當int1小於 int2時, 傳回True

    浮點數

    asr=87.22
thre=90.00
if (( $(echo "$asr < $thre" | bc -l) )); then
    return 0 # true
fi
    檔案的比對
    -e file   | 檔案是否存在
-d file   | 當file是一個目錄時, 傳回 True
-f file   | 當file是一個普通檔案時, 傳回 True
-r file   | 當file是一個可讀檔案時, 傳回 True
-s file   | 當file檔案內容長度大於0時, 傳回 True; 空白內容傳回 False
-w file   | 當file是一個可寫檔案時, 傳回 True
-x file   | 當file是一個可執行檔案時, 傳回 True

    File operators list

    Operator Returns
    -a FILE True if file exists.
    -b FILE True if file is block special.
    -c FILE True if file is character special.
    -d FILE True if file is a directory.
    -e FILE True if file exists.
    -f FILE True if file exists and is a regular file.
    -g FILE True if file is set-group-id.
    -h FILE True if file is a symbolic link.
    -L FILE True if file is a symbolic link.
    -k FILE True if file has its `sticky' bit set.
    -p FILE True if file is a named pipe.
    -r FILE True if file is readable by you.
    -s FILE True if file exists and is not empty.
    -S FILE True if file is a socket.
    -t FD True if FD is opened on a terminal.
    -u FILE True if the file is set-user-id.
    -w FILE True if the file is writable by you.
    -x FILE True if the file is executable by you.
    -O FILE True if the file is effectively owned by you.
    -G FILE True if the file is effectively owned by your group.
    -N FILE True if the file has been modified since it was last read.
    ! EXPR Logical not.
    EXPR1 && EXPR2 Perform the and operation.
    EXPR1 || EXPR2 Perform the or operation.

    布林變數應用
    # Let us Declare Two Boolean Variables
# Set this one to true
jobstatus=true
# Check it 
if [ "$jobstatus" = true ] ; then
	echo 'Okay :)'
else
	echo 'Noop :('
fi
# Double bracket format syntax to test Boolean variables in bash
bool=false
if [[ "$bool" = true ]] ; then
	echo 'Done.'
else
	echo 'Failed.'
fi
    更多範例
    # 如果前個指令執行有錯誤時，會執行兩個程序
[ ! $? -eq 0 ] && echo "Abort the process!! you can try it agian after you made change." && exit 1

# 或者
[ ! $? -eq 0 ] && {
 echo "Abort the process!! you can try it agian after you made change."
 exit 1
} 

#
if [[ $RETURN_CODE != 0 ]]; then
        echo "Zulip first start database initi failed in \"initialize-database\" exit code $RETURN_CODE. Exiting."
        exit $RETURN_CODE
fi

#
if [[ $TIMEOUT -eq 0 ]]; then
            echo "Could not connect to database server. Exiting."
            unset PGPASSWORD
            exit 1
fi
#
if (($? > 0)); then
            echo "$SECRET_KEY = $SECRET_VAR" >> "$DATA_DIR/zulip-secrets.conf"
            echo "Secret added for \"$SECRET_KEY\"."
fi
#
if test "x$newbranch" = x; then
    newbranch=`git branch -a | grep "*" | cut -d ' ' -f2`
fi

# Check router home directory.
[ -d "$PROD_HOME" ] || {
	echo "Router home directory ($PROD_HOME) not found"
	exit 1
}

# AND
autoBackupConfiguration() {
    if ([ "$AUTO_BACKUP_ENABLED" != "True" ] && [ "$AUTO_BACKUP_ENABLED" != "true" ]); then
        rm -f /etc/cron.d/autobackup
        echo "Auto backup is disabled. Continuing."
        return 0
    fi
}

# OR
if [ "$MANUAL_CONFIGURATION" = "False" ] || [ "$MANUAL_CONFIGURATION" = "false" ]; then
        databaseConfiguration
        secretsConfiguration
        authenticationBackends
        zulipConfiguration
fi

# Die if $f1 or $f2 is missing 
if [ ! -f "$f1"  ] ||  [ ! -f "$f2" ]
then
	echo "Required files are missing."
else
	echo "Let us build SFTP jail."
fi
# And
if [[ $age -ge 18 ]] && [[ $nat -eq "Indian" ]];then
    echo "You can vote!!!"
else
    echo "You can not vote"

fi

# multiple AND
if [ -e "$DATA_DIR/.initiated" ] && ([ "$FORCE_FIRST_START_INIT" != "True" ] && [ "$FORCE_FIRST_START_INIT" != "true" ]); then
    echo "First Start Init not needed. Continuing."
    return 0
fi


# one-liner
 [[ -z "$var" ]] && echo "NULL" || echo "NOT NULL"
# if age is greater than or equal to 18 then the program will print "Adult" or it will print "Minor".
[[ $age -ge 18 ]] && echo "Adult" || echo "Minor"

# Contain a substring
if [[ $var = *pattern1* ]]; then
    echo "Do something"
fi

[[ $1 != *cyberciti.biz/faq/* ]] && { printf "Error: Specify faq url (e.g., http://www.cyberciti.biz/faq/url-1-2-3/)\n"; exit 2; }

if [[ $fullstring == *"$substr"* ]];

# Regex
if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then

head="win00000:hascom_command.ksh : hostname:wintstc, monitor port#:17911"
if [[ $head =~ ^win00000.*$ ]]; then

# Check the the number of the version
[ "$(echo "$TMUX_VERSION >= 2.4" | bc)" = 1 ] || echo "The version $TMUX_VERSION is outdated"

    Two functions (Is_alert & Notify) return True

    if Is_alert && Notify; then
    echo "Send_mail"
fi

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