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Directory for this Exercise

• Go to your ex directory

      cd  ~/it244/ex

• Create an ex23 directory
  

      mkdir  ex23

• Go to your ex23 directory
  

      cd  ex23

Using test, as [ ], with Numbers

• Use test with the -eq (equality for numbers) operator
  

      [ 4 -eq 5 ] ; echo $?

  Since anything other than 0 as an exit status signals failure, this means that the equality test has failed.
  
  Be sure to use a space before and after each [ and ] character.
• Use the -eq operator with the same number on both sides
  

      [ 4 -eq 4 ] ; echo $?

  Since 0 means success, this means that the expression evaluated to true.
• Use test with the -ne (not equal for numbers) operator
  

      [ 4 -ne 5 ] ; echo $?

  0 means true.
• Use -ne again
  

      [ 4 -ne 4 ]; echo $?

  1 means false.
• Use test with the -gt (greater than) operator
  

      [ 4 -gt 5 ] ; echo $?
      [ 5 -gt 4 ] ; echo $?

• Use the -ge (greater than or equal to) operator
  

      [ 5 -ge 4 ] ; echo $?
      [ 5 -ge 5 ] ; echo $?
      [ 4 -ge 5 ] ; echo $?

• Use the -lt (less than operator)
  

      [ 4 -lt 5 ] ; echo $?
      [ 5 -lt 4 ] ; echo $?

• Use the -le (less than or equal to) operator
  

      [ 4 -le 5 ] ; echo $?
      [ 4 -le 4 ] ; echo $?
      [ 5 -le 4 ] ; echo $?

Using test with String Comparison Operators

• Use test with the = (string equality) comparison operator
  

      [ "foo" = "foo" ] ; echo $?
      [ "foo" = "bar" ] ; echo $?

• Use test with the != (string not equal) comparison operator
  

      [ "foo" != "bar" ] ; echo $?
      [ "foo" != "foo" ] ; echo $?

Using test with Single String Operators

• Use test with the -n (length greater than 0) string operator
  

      [ -n "foo" ] ; echo $?
      [ -n "" ] ; echo $?

• Use test with the -z (length is 0) string operator
  

      [ -z "" ] ; echo $?
      [ -z "foo" ] ; echo $?

Using test logical operators

• Use test with the -a (logical AND) operator

      [ 5 -lt 6 -a "foo" != "bar" ]; echo $?
      [ 5 -lt 6 -a "foo" != "foo" ]; echo $?

• Use test with the -o (logical OR) operator

      [ 5 -lt 6 -o "foo" != "foo" ]; echo $?
      [ 5 -lt 5 -o "foo" != "foo" ]; echo $?

• Use test with the ! (logical NOT) operator

      [ ! 5 -lt 5 -o "foo" != "foo" ]; echo $?
      [ ! 5 -lt 6 -o "foo" != "foo" ]; echo $?

Using test with File and Directory Operators

• Create the empty file empty.txt

      touch empty.txt

• Make empty.txt read only

      chmod 444 empty.txt

• Create the file foo.txt

      cat > foo.txt [Enter]
      foo [Enter]
      Control d

• Make sure this file is not empty

      cat foo.txt

• Give yourself full privileges to this file

      chmod 700 foo.txt

• Create the directory dir1

      mkdir dir1

• Use test with the -d (is it a directory) operator

      [ -d dir1 ]; echo $?
      [ -d foo.txt ]; echo $?

• Use test with the -e (it exists) operator

      [ -e foo.txt ]; echo $?
      [ -e bar.txt ]; echo $?

• Use test with the -f (is an ordinary file) operator

      [ -f foo.txt ]; echo $?
      [ -f dir1 ]; echo $?

• Use test with the -r (exists and is readable) operator

   
      [ -r empty.txt ]; echo $?
      [ -r xxxx.txt ]; echo $?

• Use test with the -s (exists and has a size greater than 0) operator

      [ -s foo.txt ]; echo $?
      [ -s empty.txt ]; echo $?

• Use test with the -w (exists and is writeable) operator

      [ -w foo.txt ]; echo $?
      [ -w empty.txt ]; echo $?

• Use test with the -x (exists and is executable) operator

      [ -x foo.txt ]; echo $?
      [ -x empty.txt ]; echo $?

if ... then ... else ...

• Make sure you are in your ex23 directory
  

      cd ~/it244/ex/ex23

• Using your favorite editor create the script arg_count.sh

• Test the script several times using bash with the -x option
  

      bash -x arg_count.sh
      bash -x arg_count.sh foo
      bash -x arg_count.sh foo bar
      bash -x arg_count.sh foo bar bletch

if ... then ... elif ...

• Make sure you are in your ex23 directory
  

      cd ~/it244/ex/ex23

• Using your favorite editor create the script arg_count_2.sh

• Change the permissions on arg_test.sh to make it executable
  

      chmod 755 arg_count_2.sh

• Test the script several times using bash with the -x option
  

      bash -x arg_count_2.sh
      bash -x arg_count_2.sh foo
      bash -x arg_count_2.sh foo bar
      bash -x arg_count_2.sh foo bar bletch

• Test you script
  

      ~tsoro/it244_test/ex23.sh

  When the script asks if you are ready for more, hit Return or Enter.
• Let me check your script