While (Bash Newbies)

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Contents

Overview

These are the scripts and notes from September 9, 2008's Bash Shell Scripting for Newbies session. The topic is while and the rest of Bash's compound statements.

Example 1: whileSpinner

Text of whileSpinner: 

#!/bin/bash

# New: arrays
spinner[0]=-
spinner[1]=/
spinner[2]='|'
spinner[3]=\\

n=0

echo -n " "
# new: while
while true
do
       n=$[n + 1]
       n=$((n % 4))
       echo -en "\b${spinner[$n]}"
       #sleep 1
done

format of while

Format of the while compound statement: 

while some_commands
do
    some_more_commands
done

or: 

while command; do block; done

more info on test

For the program test (and [ ]), see man test.

For the Bash builtin test (and [[ ]]), see man builtin and help test.

more info on &&

&& ...

Example 2: whileMenu

Text of whileMenu: 

#!/bin/bash

menu() {
       echo "1) Check email"
       echo "2) Surf web"
       echo "3) Edit file"
       echo "4) Spreadsheet"
       echo "5) Exit"
}

menu
while read -p "Enter an option: [1-5] " a
do
       echo
       # New: case
       case $a in
               1)
                       echo mutt
                       ;;
               one)    echo gmail
                       ;;
               2|ff)
                       echo firefox ;;
               "3"|'4')        echo openoffice
                       ;;
               v)      echo vim;;
        j*|J*|*rox*|????)
            echo Yes, Jas rox, but anyway...
            ;;
               '*')    echo exit
                       ;;
               *)      exit
                       ;;
       esac
       echo
       menu
done

format of case

Format of the case compound statement: 

case $variable in  list_of_things 
    something)
        statements
        ;;
    whatever)
        more_statements
        ;;
    whatevers)
        ...
        ;;
esac

info on globs/wildcards

For more info on globs or wildcards, see man 7 glob and man bash, section "Pattern Matching"

Example 3: whileMenu2 

#!/bin/bash

# Similar menu program, using `select'

PS3="Type in a number: "

# New: until
#while true
until ! true
do
       # New: select
       select proggy in mutt gmail firefox openoffice vim exit
       do
               [[ exit == $proggy ]] && exit
               echo
               echo Executing $proggy ...
               #$proggy
               break
       done
       echo
done

format of until 

until commands
do
    block
done

format of select 

select a_variable in a_list
do
    block
done

Example 4: whileReadStats 

#!/bin/bash

echo Products:
# pipe to while
sort -n < stats |
       while read a b
       do
               echo "$a x $b = $[ a * b]"
       done

echo Remainders:
# redirect while
while read c d; do
       echo "$c mod $d = $[c % d ]"
done < stats

File: stats 

23 878
243 3
423 43
4 54
342 0
2 78
2 1
23 32
3 326
3 1221
2 98000
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