HLdeMacBook-Air:~ hl$ more file.txt 
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10
HLdeMacBook-Air:~ hl$ 

檔案file.txt 內容如上，列印第9行內容，可以採取以下幾種方式

方式一:  tail + head

tail -n +9 filename     從第9行輸出

head -n 1 filename    輸出前1行

HLdeMacBook-Air:~ hl$ tail -n +9 file.txt 
Line 9
Line 10
HLdeMacBook-Air:~ hl$ 
HLdeMacBook-Air:~ hl$ tail -n +9 file.txt | head -n 1
Line 9
HLdeMacBook-Air:~ hl$
 

ps：不要寫成  head -n count file.txt | tail -n 1 ;   因為當file.txt 沒有count行，按這個方式就會變顯示最後一行的內容

方式二：sed

HLdeMacBook-Air:~ hl$ sed -n '9p' file.txt 
Line 9
HLdeMacBook-Air:~ hl$ sed -n '9,10p' file.txt 
Line 9
Line 10
HLdeMacBook-Air:~ hl$ 

'9,10p' : 第9～10行

方式三：awk

 NR     ordinal number of the current record

 FNR    ordinal number of the current record in the current file


HLdeMacBook-Air:~ hl$ awk NR==9 file.txt file.txt
Line 9
HLdeMacBook-Air:~ hl$ awk FNR==9 file.txt file.txt
Line 9
Line 9
HLdeMacBook-Air:~ hl$