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While loop problem

 
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# 1  
Old 12-26-2010
While loop problem
I have a while loop with -f and -o option.Can any one please tell me what that stands for?The Sample code is as follows:-
Code:
while [ ! -f $DATA/$AMPS_COMPLETE01 -o ! -f $DATA/$AMPS_COMPLETE02 -o \
! -f $DATA/$AMPS_COMPLETE03 -o ! -f $DATA/$AMPS_COMPLETE04 -o \
$PMON_COUNT -eq 0 ] 
do
  ## some processing
done

Last edited by Scott; 12-26-2010 at 09:54 AM.. Reason: Please use code tags
# 2  
Old 12-26-2010
You could find that out by reading the man page for test(1).

Code:
-f file       True if file exists and is a regular file

expression1 -o expression2
                   True if either expression1 or expression2 are true.

! negates the test (meaning "if not ...").
This User Gave Thanks to Scott For This Post:
Param0073
# 3  
Old 12-26-2010
Thanks for the reply.I got the information from the man page ,but still one more doubt was "what the back slash is used for in the code".
# 4  
Old 12-26-2010
It is a line-continuation character, allowing you to span commands over multiple lines. This is usually done to aid readability.
This User Gave Thanks to Scott For This Post:
Param0073
# 5  
Old 12-26-2010
Hi Scottn,

Thanks for ur explanation btw, even I made quite many shell scripts(just simple scripts I think), but never know we can continue line by using \

Gotta try it tomorrow

Thanks Param0073 for asking this Smilie
# 6  
Old 12-29-2010
Backslashes are used to escape the following character.. So when you backslash, and then hit enter, it is not interpreted as a request for the shell to execute the preceding code, only to go to the next line and continue.. You could use this to do longer scripts in the shell instead of just one liners.

That's how I understand it at least.

Just like when you have spaces in a path, instead of quotes, you can escape them like : ~/My\ Directory/files/work\ stuff/Superchams.sh
# 7  
Old 12-29-2010
You can also use an until statement, which may make it a bit more readable (also -o and -a are deprecated):
Code:
until [ -f $DATA/$AMPS_COMPLETE01 ] && [ -f $DATA/$AMPS_COMPLETE02 ] && \
      [ -f $DATA/$AMPS_COMPLETE03 ] && [ -f $DATA/$AMPS_COMPLETE04 ] && \
      [ $PMON_COUNT -ne 0 ] 
do

 
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