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第一個流程控制是 "if"，學過程式語言的讀者，應該很熟悉，不需特殊說明，讀者應可瞭解其用法，以下是各種格式：

if then

if command
then       
    then-commands 
fi

if test condition
then       
    then-commands 
fi

if [ condition ]
then       
    then-commands 
fi

else


if [ condition ]
then       
    then-commands 
else           
    else-commands
fi

elif

			 
if [ condition1 ]
then        
    commands1 
elif [ condition2 ] 
then           
    commands2   
else         
    commands3
    commands3
fi