Want to execute rest of the script after the file is ready ...

csaha · #1 (**permalink**) 09-23-2006

Hi All

I have a requirement like, where a file gets generated in a particular dir and once the file is ready and available then I want to execute rest of the script, because untill and unless the file exists and is available there is no use of running rest of the commands in that script.

Any idea how can I achieve this?

Thanks in advance to all

aigles · #2 (**permalink**) 09-23-2006

The following code waits for existence of a file.

Code:

required_file=/path/to/file
test_interval=30
while [ ! -f $required_file]
do
   sleep $test_interval
done
echo "File $required_file available."

Another form with bash, ksh :

Code:

required_file=/path/to/file
test_interval=30
until[ -f $required_file]
do
   sleep $test_interval
done
echo "File $required_file available."

Jean-Pierre.

dsravan · #3 (**permalink**) 09-24-2006

Aigles,

while [ ! -f $required_file]

does this signify while the requried file is not a file to sleep for so much time and once that file is there start your next process. Please let me know.

Thanks,

reborg · #4 (**permalink**) 09-24-2006

More or less, -f means "exists and is a file", but you have understood the logic correctly.

sayonm · #5 (**permalink**) 09-25-2006

but wht if the file that is getting created is a big file and it takes some time for that file to get created, then the above codes wont help....i am teling this from my experience

but i dont understand why we have to do anything....(like [ ! -f filename ])
because the following will also work fine

Code:

head -100 abc.txt > temp # where the file gets created
wc -m temp > count # the rest of the code

line two only will be excuted after line 1 gets executed first !!!
someone please clearify.........

aigles · #6 (**permalink**) 09-25-2006

Quote:

but wht if the file that is getting created is a big file and it takes some time for that file to get created, then the above codes wont help....i am teling this from my experience

Exact according to my experiment too.
A possible solution is to add a test to control if the file is opened by a process (bulletproof) :

Code:

required_file=txt.txt
test_interval=30
while true
do
   if [ -f $required_file ]
   then
      echo "$0 - File exists !"
      if fuser $required_file 2>&1 | awk -F':[[:space:]]*' '{exit ($2=="" ? 0 :1)}'
      then
         break
      else
         echo "$0 - File in use !"
      fi
   fi
   sleep $test_interval
done
echo "File $required_file available."

Another way is to to modify the source application of the file : After the file creation, a file flag is created to indicate that the file is available.
Instead of checking the file existence, le waiting process check the flag file.

Quote:

but i dont understand why we have to do anything....(like [ ! -f filename ])
because the following will also work fine

Code:

head -100 abc.txt > temp # where the file gets created
wc -m temp > count # the rest of the code

line two only will be excuted after line 1 gets executed first !!!
someone please clearify.........

This will not work.
If the file doesn't exist, the head command will fail.

Jean-Pierre.

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