Shell Programming and Scripting

If a file is compressed, how can i uncompress on the fly using pipes(handling this in the shell script depending on the command line arguments passed to the script)

ex: ex_pr.sh -d disable -f ex_pr_1212.log.Z

This is all very dependent on how your shell script handles this. Seeing as you are supplying the compressed file as an argument to option "-f", then I would assume that the actual file opening and processing is handled internally within the script.

If, however, the script read from stdin, you could do
zcat somefile.Z | myscript

You can't do
myscript -f `zcat somefile.Z`
because that would expand the whole file and supply each word as an argument. Definitely not what you want!

You could add a handler to your shell script that looks at the supplied file's extension, and invokes zcat to read the file if it has a ".Z" extension.

EDIT: Please give your threads a more descriptive title than just "Ques". A descriptive, useful title will help people who have the appropriate knowledge find your post and help you out. Something like "Compressed file as a script argument" or similar would have been better for this post.

Cheers
ZB

If i pass ex_p1.log.Z as the argument at the command line
i want inside the script ex_p1.log(as the file name), i.e checking if the file extension is .Z(how ?), if it has .Z i want to uncompress so
ex_p1.log.Z is replaced as ex_p1.log (using pipes on fly -how ?)

Thanks

$ echo "ex_pr_1212.log.Z" | grep ".Z$"
ex_pr_1212.log.Z
$ echo $?
0
$ echo "ex_pr_1212.log" | grep ".Z$"
$ echo $?
1
$

Make sure you backslash escape the dot "." as it is a metacharacter (any char).

The code above will also match anything ending in an upper-case Z, e.g.

echo "something.ZAZZ" | grep '.Z$'
will match.

You need
echo "something.ZAZZ" | grep '\.Z$' (exit code 1)
echo "foo.log.Z" | grep '\.Z$' (exit code 0 - correct)

EDIT:

To get you on the right track. Let's assume you write a script, foo.sh. You call foo.sh something like this

$ ./foo.sh myfile

Where myfile can sometimes have a .Z extension.

Within your code, do something like (I've made this fairly verbose so you can see what's happening)

Code:

#!/bin/sh

inputfile=$1

echo "$inputfile" | grep '\.Z$' >/dev/null 2>&1
if [ "$?" -eq "0" ]; then
   # yay, it's been compressed
   zcat $inputfile | while read line
   do
     echo "Heres the line... $line"
   done
else
   # assume it's not compressed, you could check for .gz, etc
   while read line
   do
     echo "Heres the line... $line"
   done < $inputfile
fi

exit 0

This is untested, but should work.

Cheers
ZB

$uncompress ex_pr1.dmp.Z > ex_pr12.dmp

I want to write the o/p of .Z to a different file name like ex_pr12.dmp

I tried like this but the ex_pr12.dmp has 0 bytes.
If there is a way to write to another file name please let me know.

Thanks

u can try either

uncompress -c x.Z > somefile

or

zcat x.Z > somefile


in both the cases, u still have x.Z unmmodified.

U can remove it if u want ...