1.12 Generating a Range of Numbers
1.12.1 Description
This function script counts from and to a range of numbers.
Flavors: AT&T
and BSD
Shell: sh
This script counts between a range of numbers that are passed
through STDIN. It is sometimes necessary to generate a range of numbers to be
used within a command or another shell script.
#! /bin/sh
LO=$1;HI=$2
while [ $LO -le $HI ]
do
echo -n $LO " "
LO=`expr $LO + 1`
done
Line 1: Define the shell being used.
Line 3: Set the variable $LO to the
first argument passed to STDIN. Set the variable $HI
to the second argument passed to STDIN.
Line 5: Process through the range of numbers until $LO
is greater than $HI.
Line
7: Output the current number in $LO.
Line 8: Increment the number in $LO.
Line 9: Exit if $LO is greater than
$HI; otherwise, continue with the next number in
the range.
If the previous script is named count
and executed
$ count 4 13
4 5 6 7 8 9 10 11 12 13
the script will count from 4 to 13 without any carriage returns.
Reason
This script is very useful. The output from the script can be
passed to other scripts to enhance their functionality. Shell scripts do not
have the capability to count within a range of numbers. This little function
script provides this capability.
Real World Experience
As administrators, you are often faced with writing shell scripts
that require some kind of loop within them. Performing a loop around a range
of numbers can get messy if there is a large range involved. By using the counting
script described previously, a lengthy for loop
can be shortened to a call to the counting script.
Here is what you have to do when there is no counting script to
call:
#! /bin/sh
STRING="The quick brown fox jumped really high"
for i in `echo "5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20"`
do
echo $STRING | cut -c$i
done
Compare that to this, when the counting script is available:
#! /bin/sh
STRING="The quick brown fox jumped really high"
for i in `count 5 20`
do
echo $STRING | cut -c$i
done
This script simply prints out each letter between the fifth and
twentieth characters in the string on a line by itself. If the script is needed
to process a large range of numbers, the first method of counting with an echo
command isn't too efficient. This little function script is great for processing
strings, characters, files, and directories--there are many possible uses for
this script.
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