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IF-then-elif $cat greetings # #Greetings #A program sample using the if-then-elif construct #This program displays greetings according to the time of the day # set `date` #set positional variable to date hour=$4 #store part of date string that shows the hour if [ "$hours" –lt 12 ] then echo "GOOD MORNING" elif [ "$hour" lt 18 ] then echo "GOOD AFTERNOON" else echo "GOOD EVENING" fi
FOR LOOP
for loopindex in argument-list do Commands done
[wmorales@rc02uxas01 scripts]$ cat fruit.sh for fruit in apples oranges pears bananas do echo "$fruit" done echo "Task complete."
[wmorales@rc02uxas01 scripts]$ bash fruit.sh apples oranges pears bananas Task complete. [wmorales@rc02uxas01 scripts]$ For for loop-index do commands done Example: args implies for args in "$@" $cat for_test for args do print $args done $ for_test candy gum chocolate #call to program candy gum chocolate
While loop
$cat count #!/bin/bash number=0 while [ "$number" -lt 10 ] do echo -n "$number" let number="$number"+1 done echo Arithmetic in bash In any of the shells, arithmetic may be done using the expr command x=2 y=`expr $x + 2` bash also allows you to do arithmetic using the let command x=3 let y=$x+4 Numeric Test Operators * Table of The test Command Numeric Test Operators Operator Meaning -eq Is number 1 equal to number2 ? -ne Is number1 not equal to number2 ? -gt Is number 1 great than number2 ? -ge Is number1 great than or equal to number2 ? -lt Is number 1 less than number2 ? -le Is number1 less than or equal to number2 ?
UNTIL
$cat until secretname=jenny name=noname echo "Try to guess the secret name!" echo until [ "$name" = "$secretname" ] do echo -n "Your guess: " read name done echo "Very good."
$cat uon #!/bin/bash # # uon: let me know if xxx is on the system # until who | grep "$1" > /dev/null #redirect the output of grep do sleep 30 #wait half minute done echo "$1 is logged on." exit 0
CASE
$cat case1 echo -n "Enter A, B, or C: " read letter case "$letter" in A) echo "You entered A" ;; #;; means break out of the case B) echo "You entered B" ;; C) echo "You entered C" ;; *) # * catch all, if all fail echo "You did not enter A, B, or C" ;; esac
$cat case2 echo -n "Enter A, B, or C: " read letter case "$letter" in a|A) echo "You entered A" ;; b|B) echo "You entered B" ;; c|C) echo "You entered C" ;; *) echo "You did not enter A, B, or C" ;; esac
$cat command menu #!/bin/bash # menu interface to simple commands echo -e "\n COMMAND MENU\n" echo " a. Current date and time" echo " b. Users currently logged in" echo " c. Name of the working directory" echo -e " d. Contents of the working directory\n" echo -e "Enter a, b, c, or d: \c" read answer echo case "$answer" in a) date ;; b) who ;; c) pwd ;; d) ls ;; *) echo "There is no selection: $answer" ;; esac
File Test Operators Table of The test Command File Test Operators Operator Example Meaning -r -r filename Does filename exist and is it readable? -w -w filename Does filename exist and is it writeable? -s -s filename Does filename exist and have a nonzero length? -f -f filename Does filename exist, but is it not a directory file? -d -d filename Does filename exist,and is it a directory file? Example" $cat svi #!/bin/bash # The save and invoke vi program # This program check for the file’s existence # if test $# = 1 #check of the number of argument then if test –f $1 # check for the file existence then cp $1 $HOME/keep #copy and invoke vi vi $1 else echo " file not found. Try again" fi else echo " You must specify a file name. Try again." fi |
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