-n, --line-number  print line number with output lines

-n, --lines=K output the last K lines, instead of the last 10; or use -n +K to output lines starting with the Kth

tail -n 5 f.txt //显示f.txt最后5行
tail -n +5 f.txt //从第5行开始，显示f.txt

-n, --lines=[-]K  print the first K lines instead of the first 10; with the leading `-', print all but the last

head -n 5 f.txt //显示f.txt最前面5行
tail -n -5 f.txt //从倒数第5行开始，显示前面的所有内容

tail -n +8786810 err.log |head -n 30

sed -n "n1,n2p" f.txt //查看f.txt n1行到n2行之间的内容

sed -n "8786810,8786840p" err.log

grep -n "xxx"  str.txt   # -n 打印字符 “xxx” 在文件 “str.txt” 所在的行数前缀

grep -n "xxx"  str.txt | head -1

grep -n "xxx"  str.txt | tail -1

grep -n "xxx"  str.txt | head -2 | tail -1      # 先取出前两行，然后取最后一行

grep -n "xxx"  str.txt | cut -d ":" -f 1

grep -n "xxx"  str.txt | head -1 | cut -d ":" -f 1

#!/bin/bash

rm -rf ret.txt

total=`wc -l $1 | awk '{print $1}'`
echo "total = $total"

num=1
while read line
do
echo $line

ret=`grep -n $line $2 | head -1` 
echo $ret

if [ -z $ret ]; then
num2=$total
echo "null num2 = $total"
else
num2=`echo $ret | cut -d ":" -f 1`
echo "num2 = $num2"
fi

echo $num
change=`expr $num2 - $num`
echo "$num2 - $num = $change"

num=`expr $num + 1`

echo "$line=$change"  ret.txt
done < $1


cat ret.txt