Linux ——结构化语句

if  command    #条件 
then
    command
fi

if  command    #条件 
then
    commands
else
    commands
fi

if  command1    #条件 
then
    commands
else
    if commands2
    then
        commands
    fi
fi

例如
if [ 1 -eq 1 ]
then 
echo "Hi!"
else 
echo "???"
fi

例如
if [ $? -eq 0]
then 
touch ok.txt
else
fi

for i in list
do
   commands
done

例如
for i in 1 2 3 4 5 6 
do
echo ${i} "Hi!"
sleep 3s
done

list="CDS exon gene start_codon"
for i in ${list}
do
echo "This feature is ${i}"
done

反引号``  ``里面的是一个命令，会被优先执行
for i in `ls file*`
do
mv ${i} ${i}.txt
done

感受下
a=gene
echo $a1
echo ${a}1

while read id
do 
  commands
done

ls file* | while read id    #选中文件传给变量id
do
mv ${id} ${id}.txt     #改名字
done

id=example.test.fq
echo $id
echo ${id#*.}
​
echo ${id#t}
echo ${id##*t}
​
echo ${id%.*}
echo ${id%%.*}

id=data.tar.gz
echo ${id/ta/xy}
echo ${id//ta/xy}

id=data.tar.gz
echo ${#id}
echo ${id:3}    #索引位置从0开始
echo ${id:3：5}
echo ${id:3：-1}