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Select loop

2024-08-17 23:38:12   223人阅读

The Bash Shell also offer select Loop, the syntax is:

select varName in list
do
    command1
    command2
    ....
    ......
    commandN
done

OR (combine both select and case statement)

select varName in list
do
	case $varName in
		pattern1)
			command1;;
		pattern2)
			command2;;
		pattern1)
			command3;;
		*)
			echo "Error select option 1..3";;
	esac			
done
  • Select command use PS3 variable to print its prompt.
  • Each word in list is printed on screen preceded by a number.
  • If the line consists of the number corresponding to one of the displayed words (from the list), then varName is set to that word. You can use if..else.fi or case..in..esac to make a decision.
  • If the line is empty, WORDS and the prompt are redisplayed.
  • If EOF (end of file) is read, the command completes.
  • The loop continues until a break (CTRL+C) is encountered.

Example

Create a shell script called select.sh:

#!/bin/bash
# Set PS3 prompt
PS3="Enter the space shuttle to get more information : "

# set shuttle list
select shuttle in columbia endeavour challenger discovery atlantis enterprise pathfinder
do
    echo "$shuttle selected"
done

Save and close the file. Run it as follows:

chmod +x select.sh
./select.sh

Sample outputs:

/tmp/x.sh
1) columbia    3) challenger  5) atlantis    7) pathfinder
2) endeavour   4) discovery   6) enterprise
Enter the space shuttle name to get more information : 1
columbia selected
Enter the space shuttle name to get more information :

Combining the select and the case statement

Another select loop example and decision making does with case..in..esac statement (selectshuttle.sh):

#!/bin/bash
# The default value for PS3 is set to #?.
# Change it i.e. Set PS3 prompt
PS3="Enter the space shuttle to get quick information : "
 
# set shuttle list
select shuttle in columbia endeavour challenger discovery atlantis enterprise pathfinder
do
	case $shuttle in
		columbia)
			echo "--------------"
			echo "Space Shuttle Columbia was the first spaceworthy space shuttle in NASA‘s orbital fleet."
			echo "--------------"
			;;
		endeavour)
			echo "--------------"		
			echo "Space Shuttle Endeavour is one of three currently operational orbiters in the Space Shuttle." 
			echo "--------------"		
			;;
		challenger) 
			echo "--------------"				
		    echo "Space Shuttle Challenger was NASA‘s second Space Shuttle orbiter to be put into service."
			echo "--------------"				    
			;;		
		discovery) 
			echo "--------------"		
			echo "Discovery became the third operational orbiter, and is now the oldest one in service."
			echo "--------------"							
			;;		
		atlantis)
			echo "--------------"		
			echo "Atlantis was the fourth operational shuttle built."
			echo "--------------"							
			;;
		enterprise)
			echo "--------------"		
			echo "Space Shuttle Enterprise was the first Space Shuttle orbiter."
			echo "--------------"							
			;;		
		pathfinder)
			echo "--------------"		
			echo "Space Shuttle Orbiter Pathfinder is a Space Shuttle simulator made of steel and wood."
			echo "--------------"							
			;;
		*)		
			echo "Error: Please try again (select 1..7)!"
			;;		
	esac
done

Save and close the file. Run it as follows:

chmod +x selectshuttle.sh
./selectshuttle.sh

Sample outputs:

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selectshuttle.sh output

Select loop


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