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Name

while, until - shell built-in functions to repetitively execute a set of actions while/until conditions are evaluated TRUE

Synopsis

sh

while [ conditions ]; do actions ; done
until [ conditions ]; do actions ; done

csh

while (conditions)
...    # do actions
end

ksh

while [ conditions ]; do actions ; done
until [ conditions ]; do actions ; done

Availability

SUNWcsu

Description

sh

A while command repeatedly executes the while conditions and, if the exit status of the last command in the conditions list is 0, executes the do actions; otherwise the loop terminates. If no commands in the do actions are executed, then the while command returns a 0 exit status; until may be used in place of while to negate the loop termination test.

csh

While conditions is TRUE (evaluates to nonzero), repeat commands between the while and the matching end statement. The while and end must appear alone on their input lines. If the shell’s input is a terminal, it prompts for commands with a question-mark until the end command is entered and then performs the commands in the loop.

ksh

A while command repeatedly executes the while conditions and, if the exit status of the last command in the conditions list is zero, executes the do actions; otherwise the loop terminates. If no commands in the do actions are executed, then the while command returns a 0 exit status; until may be used in place of while to negate the loop termination test.

loop interrupts

The built-in command continue may be used to terminate the execution of the current iteration of a while or until loop, and the built-in command break may be used to terminate execution of a while or until command.

Examples

In these examples, the user is repeated prompted for a name of a file to be located, until the user chooses to finish the execution by entering an empty line.

sh


    filename=anything
    while [ $filename ]
    do
        echo "file?"
        read filename        # read from terminal 
        find . -name $filename -print
    done

The brackets surrounding $filename are necessary for evaluation. (See the test built-in command in the if(1) man page). Additionally, there must be a blank space separating each bracket from any characters within.

csh


    set filename = anything
    while ( "$filename" != "" )
        echo "file?"
        set filename = $<        # read from terminal 
        find . -name $filename -print
    end
        

ksh

Use the same syntax as in the Bourne shell, sh, example above.

See Also

break(1) , csh(1) , if(1) , ksh(1) , sh(1)

Notes

Both the Bourne shell, sh, and the Korn shell, ksh, can use the semicolon and the carriage return interchangeably in their syntax of the if, for, and while built-in commands.

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