topic Re: doubt on while loop in Operating System - HP-UX

doubt on while loop

laiju.c.babu — Tue, 05 Feb 2013 05:35:57 GMT

Hi Gurus,

In a script i saw a while loop having below condition

while [[ -a $LOCK_FILE ]]

do { ===== done }

could you please tell me what this while condition will do. This LOCK_FILE is decalred as /tmp/audit.lock

Regards

Re: doubt on while loop

Matti_Kurkela — Tue, 05 Feb 2013 06:34:40 GMT

The expression with double square brackets is a conditional expression that is parsed by the shell that is executing the script, so you should identify the shell that is used to run the script. Is it sh, ksh or something else?

For example, if the script is run using /sbin/sh or /usr/bin/sh in HP-UX, the sh-posix(1) man page lists all the possible conditions for a double-square-bracket conditional expression in a chapter titled Conditional Expressions.

In this case, -a <filename> means "the condition is true if <filename> exists". The test completely ignores the type of <filename>: it might actually be a directory, a symbolic link, a named pipe, or something else.

The loop will run as long as /tmp/audit.lock exists.

You might have been confused because in a single-square-bracket expression, the -a has a completely different meaning: it appears as <condition> -a <condition> and means that the expression is true only if both conditions are true.

Re: question on conditional expression

Dennis Handly — Tue, 05 Feb 2013 08:33:44 GMT

Be careful if replacing it with -e, that's only for sh, not ksh.

Re: doubt on while loop

laiju.c.babu — Tue, 05 Feb 2013 08:35:20 GMT

Hi MK,

Thanks for the reply, the shell on which this script is executing is /usr/bin/ksh.

Regards