Can I attach a variable to a tail command?












5














Is this possible, if not, is there a better I can do it?



Example:



Number of log entries: 3



log=$(home/admin17/folder/data_log)

read -p "Number of log entries" num

cat $log | tail -n $num





shell-script







share|improve this question





























    5














    Is this possible, if not, is there a better I can do it?



    Example:



    Number of log entries: 3



    log=$(home/admin17/folder/data_log)
    
read -p "Number of log entries" num
    
cat $log | tail -n $num





    shell-script







    share|improve this question



























      5












      5








      5







      Is this possible, if not, is there a better I can do it?



      Example:



      Number of log entries: 3



      log=$(home/admin17/folder/data_log)
      
read -p "Number of log entries" num
      
cat $log | tail -n $num





      shell-script







      share|improve this question















      Is this possible, if not, is there a better I can do it?



      Example:



      Number of log entries: 3



      log=$(home/admin17/folder/data_log)
      
read -p "Number of log entries" num
      
cat $log | tail -n $num





      shell-script




      shell-script






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 days ago









      terdon♦

      129k31252427




      129k31252427










      asked 2 days ago









      User101User101

      584




      584






















          1 Answer
          1






          active

          oldest

          votes


















          13














          The var=$(command) notation runs command and assigns its output to var. Since home/admin17/folder/data_log is a file and not a command, that should give you an error:



          log=$(home/admin17/folder/data_log)
          
bash: home/admin17/folder/data_log: command not found


          If you want to save the file name as a variable, you need:



          log=home/admin17/folder/data_log


          Then, the rest should work as you expect:



          log=home/admin17/folder/data_log
          
read -p "Number of log entries" num
          
cat $log | tail -n $num


          Or, avoiding the Useless Use of Cat (UUoC):



          log=home/admin17/folder/data_log
          
read -p "Number of log entries: " num
          
tail -n "$num" "$log"





          share|improve this answer



















          • 1




            Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
            – Sergiy Kolodyazhnyy
            2 days ago











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          active

          oldest

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          13














          The var=$(command) notation runs command and assigns its output to var. Since home/admin17/folder/data_log is a file and not a command, that should give you an error:



          log=$(home/admin17/folder/data_log)
          
bash: home/admin17/folder/data_log: command not found


          If you want to save the file name as a variable, you need:



          log=home/admin17/folder/data_log


          Then, the rest should work as you expect:



          log=home/admin17/folder/data_log
          
read -p "Number of log entries" num
          
cat $log | tail -n $num


          Or, avoiding the Useless Use of Cat (UUoC):



          log=home/admin17/folder/data_log
          
read -p "Number of log entries: " num
          
tail -n "$num" "$log"





          share|improve this answer



















          • 1




            Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
            – Sergiy Kolodyazhnyy
            2 days ago
















          13














          The var=$(command) notation runs command and assigns its output to var. Since home/admin17/folder/data_log is a file and not a command, that should give you an error:



          log=$(home/admin17/folder/data_log)
          
bash: home/admin17/folder/data_log: command not found


          If you want to save the file name as a variable, you need:



          log=home/admin17/folder/data_log


          Then, the rest should work as you expect:



          log=home/admin17/folder/data_log
          
read -p "Number of log entries" num
          
cat $log | tail -n $num


          Or, avoiding the Useless Use of Cat (UUoC):



          log=home/admin17/folder/data_log
          
read -p "Number of log entries: " num
          
tail -n "$num" "$log"





          share|improve this answer



















          • 1




            Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
            – Sergiy Kolodyazhnyy
            2 days ago














          13












          13








          13






          The var=$(command) notation runs command and assigns its output to var. Since home/admin17/folder/data_log is a file and not a command, that should give you an error:



          log=$(home/admin17/folder/data_log)
          
bash: home/admin17/folder/data_log: command not found


          If you want to save the file name as a variable, you need:



          log=home/admin17/folder/data_log


          Then, the rest should work as you expect:



          log=home/admin17/folder/data_log
          
read -p "Number of log entries" num
          
cat $log | tail -n $num


          Or, avoiding the Useless Use of Cat (UUoC):



          log=home/admin17/folder/data_log
          
read -p "Number of log entries: " num
          
tail -n "$num" "$log"





          share|improve this answer














          The var=$(command) notation runs command and assigns its output to var. Since home/admin17/folder/data_log is a file and not a command, that should give you an error:



          log=$(home/admin17/folder/data_log)
          
bash: home/admin17/folder/data_log: command not found


          If you want to save the file name as a variable, you need:



          log=home/admin17/folder/data_log


          Then, the rest should work as you expect:



          log=home/admin17/folder/data_log
          
read -p "Number of log entries" num
          
cat $log | tail -n $num


          Or, avoiding the Useless Use of Cat (UUoC):



          log=home/admin17/folder/data_log
          
read -p "Number of log entries: " num
          
tail -n "$num" "$log"






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 2 days ago









          Nasir Riley

          2,406239




          2,406239










          answered 2 days ago









          terdon♦terdon

          129k31252427




          129k31252427








          • 1




            Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
            – Sergiy Kolodyazhnyy
            2 days ago














          • 1




            Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
            – Sergiy Kolodyazhnyy
            2 days ago








          1




          1




          Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
          – Sergiy Kolodyazhnyy
          2 days ago




          Note also that the path is relative to user's current working directory. If the user wants to use same file regardless of where they are currently in the directory tree, the path has to be absolute, so probably /home/admin17/folder/data_log
          – Sergiy Kolodyazhnyy
          2 days ago


















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