02 介绍

   1:   

   2:  #Cleanup

   3:  # Run as root, of course

   4:   

   5:  cd /var/log

   6:  cat /dev/null > messages

   7:  cat /dev/null > wtmp

   8:   

   9:  echo "Log cleaned up."

   1:  #!/bin/bash

   2:  # Proper header for a Bash script.

   3:   

   4:  # Cleanup, version 2

   5:   

   6:  # Run as root, of course.

   7:  # Insert code here to print error message and exit if not root.

   8:   

   9:  LOG_DIR=/var/log

  10:  # Variables are better than hard-coded values.

  11:  cd $LOG_DIR

  12:   

  13:  cat /dev/null > messages

  14:  cat /dev/null > wtmp

  15:   

  16:  echo "Logs cleaned up."

  17:   

  18:  exit # The right and proper method of "exiting" from a script.

   1:  #!/bin/bash

   2:  # Cleanup, version 3

   3:   

   4:  # Warning:

   5:  # ---------------------------------------------

   6:  #       This script uses quite a number of features that will be explained

   7:  #+      later on.

   8:  #       By the time you‘ve finished the first halt of the book,

   9:  #+      there should be nothing mysterious about it.

  10:   

  11:   

  12:   

  13:  LOG_DIR=/var/log

  14:  ROOT_UID=0              # only users with $UID 0 have root privileges.

  15:  LINES=50                # default number of lines saved.

  16:  E_XCD=66                # can‘t change directory ?

  17:  E_NOTROOT=67    # Non-root exit error.

  18:   

  19:   

  20:   

  21:   

  22:  # Run as root, of course.

  23:  if [ "$UID" -ne "$ROOT_UID" ]

  24:  then

  25:          echo "Must be root to run this script."

  26:          exit $E_NOTROOT

  27:  fi

  28:   

  29:  if [ -n "$1" ]

  30:  # Test if command line argument present(non-empty).

  31:  then

  32:          lines=$1

  33:  else

  34:          lines=$LINES    # default, if not specified on command line.

  35:  fi

  36:   

  37:   

  38:  #       Stephane Chazelas suggests the following,

  39:  #+      as a better way of checking command line arguments,

  40:  #+      but this is still a bit advanced for this stage of the tutorial.

  41:  #

  42:  #               E_WORNGARGS=65  # Non-numerical argument (bad arg format)

  43:  #

  44:  #               case "$1" in

  45:  #               ""              ) lines=50;;

  46:  #               *[!0-9]*) echo "Usage: `basename $0` file-to-cleanup"; exit $E_WRONGARGS;;

  47:  #               *               ) lines=$1;;

  48:  #               esac

  49:  #*      Skip ahead to "Loops" chapter to decipher all this.

  50:   

  51:  cd $LOG_DIR

  52:   

  53:  if [ `pwd` != "$LOG_DIR" ]      # or    if ["$PWD" != "$LOG_DIR" ]

  54:                                  # Not in /var/log?

  55:  then

  56:          echo "Can‘t change to $LOG_DIR."

  57:          exit $E_XCD

  58:  fi              # Doublecheck if in right directory, before messing with log file.

  59:   

  60:  # far more efficient is:

  61:  #

  62:  # cd /var/log || {

  63:  #       echo "Cannot change to necessary directory." >&2

  64:  #       exit $E_XCD;

  65:  # }