linux shell

1.+到n

for i in {1..n}
do
a=$(($a+$i))
done
echo $a

2.

写一个脚本、输入如下效果
0
01
012
0123
01234
012345
0123456
01234567
012345678
0123456789

for((a=0;a<=9;a++))
do
q[$a]=$a
#echo $((q[$a]))
for((b=0;b<=a;b++))
do
echo -e "$((q[$b]))c"
done
echo " "
done

3.输出

0
101
21012
3210123
432101234

···

for((a=0;a<=9;a++))
do
q[$a]=$a
#echo $((q[$a]))
for((b=a;b>0;b--))
do
echo -e "$((q[$b]))c"
done
for((b=0;b<=a;b++))
do
echo -e "$((q[$b]))c"
done
echo " "
done

4.

输出 99 乘法表

for((a=0;a<=9;a++))
do
q[$a]=$a
for((b=1;b<=a;b++))
do
echo -e "----- $((q[$b]))X$((q[$a]))=$(($((q[$a]))*$((q[$b]))))c ----- "
done
echo " "
done

 5修改yum

cd /etc/yum.repos.d/
for a in CentOS-Base.repo CentOS-CR.repo CentOS-Debuginfo.repo CentOS-fasttrack.repo CentOS-Media.repo CentOS-Sources.repo CentOS-Vault.repo;do
mv $a $a.bak
done
mv ./CentOS-Media.repo.bak ./CentOS-Media.repo

回复yum

cd /etc/yum.repos.d/
for a in CentOS-Base.repo CentOS-CR.repo CentOS-Debuginfo.repo CentOS-fasttrack.repo CentOS-Media.repo CentOS-Sources.repo CentOS-Vault.repo;do
mv $a.bak $a
done