Decompress files from a single DAT file

What do you mean? You need an disk image you can load as a ramdisk? What should be in there? Most disk images aren't compressed but they can be.
 
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I'd like to decompress image .dat file, change some files
and after changes compress back to a single .dat file.
 
extension doesn't tell anything about actual file type....

try using $ file -i [i]filename[/i] and show output....
It may fail to determinate correct file type, but it's much better than file extensions

also it might be good idea to look at file with binary editor/viewer. editors/hte is my favourite


mostly Windows use file extensions to determinate file type.... I could rename some readme.txt to readme.png and many apps in windows would be confused...
That's why I dislike any File Managers that determinate file types by extensions

EDIT:
also what makes you think it's compressed?
 
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Code: 
# file -i ramdisk.dat
ramdisk.dat: application/x-gzip
# file -s ramdisk.dat
ramdisk.dat: gzip compressed data, was "ramdisk.dat.initrd", from FAT filesystem (MS-DOS, OS/2, NT), last modified: Tue Jan 13 01:00:25 2009
 
If file is correct about what it is, you just need to decompress it with gunzip, create a vnode type md device from it with mdconfig(8), mount the md device as a msdos file system, modify the files, and then reverse.

Code: 
gunzip -N ramdisk.dat
mdconfig -a -t vnode -f ramdisk.dat.inird
mount_msdosfs /dev/mdX /wherever
 
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Thx, but I'm getting this problem:
Code: 
# gunzip -N ramdisk.dat
gunzip: ramdisk.dat: unknown suffix -- ignored
# gunzip -N ramdisk.dat > ramdisk.dat.inird
gunzip: ramdisk.dat: unknown suffix -- ignored

Perhaps:
Code: 
# gunzip -dc ramdisk.dat > ramdisk.dat.inird
# mdconfig -a -t vnode -f ramdisk.dat.inird
md0
# mount_msdosfs /dev/md0 /tmp/cc
mount_msdosfs: /dev/md0: : Invalid argument
 
I'm guessing it's not a compressed FAT file system image then. So what is it?

If data can't be identified, it can't be used. If you don't know what it is then you'll need to first try figure that out with hexdump(1).
 
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You use tar with the "-z" flag. From man 1 tar
Code: 
     -z      (c mode only) Compress the resulting archive with gzip(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes gzip
             compression automatically when reading archives.
An example
Code: 
$ tar cvzf alllogs.tgz *log

a mailman-port.log
a pkgadd.log
a postfix-postfix-2.5.9,2.tbz.log
a postfix-re-pkg_add.log

$ file alllogs.tgz 
alllogs.tgz: gzip compressed data, from Unix, last modified: Thu Dec 31 20:03:53 2009

$ tar xvzf alllogs.tgz -C /tmp

x mailman-port.log
x pkgadd.log
x postfix-postfix-2.5.9,2.tbz.log
x postfix-re-pkg_add.log

$ ls -l /tmp

total 1312
[snip]
-rw-r--r--  1 root  wheel     264919 Dec 25 03:36 mailman-port.log
-rw-r--r--  1 root  wheel     917943 Dec 23 23:43 pkgadd.log
-rw-r--r--  1 root  wheel      30240 Dec 24 01:10 postfix-postfix-2.5.9,2.tbz.log
-rw-r--r--  1 root  wheel      55429 Dec 24 00:13 postfix-re-pkg_add.log
 
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killasmurf86 said:
try running $ file -i ... on decompressed image
See what it tells you
Click to expand...

Code: 
# file -i ramdisk.dat.inird
ramdisk.dat.inird: application/x-empty
 
fronclynne said:
Might try # mount_msdosfs /dev/md0s1 /tmp/cc . . .
Click to expand...
Code: 
# mount_msdosfs /dev/md0s1 /tmp/cc
mount_msdosfs: /dev/md0s1: : No such file or directory
 
J65nko said:
You use tar with the "-z" flag. From man 1 tar
Code: 
     -z      (c mode only) Compress the resulting archive with gzip(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes gzip
             compression automatically when reading archives.
An example
Code: 
$ tar cvzf alllogs.tgz *log

a mailman-port.log
a pkgadd.log
a postfix-postfix-2.5.9,2.tbz.log
a postfix-re-pkg_add.log

$ file alllogs.tgz 
alllogs.tgz: gzip compressed data, from Unix, last modified: Thu Dec 31 20:03:53 2009

$ tar xvzf alllogs.tgz -C /tmp

x mailman-port.log
x pkgadd.log
x postfix-postfix-2.5.9,2.tbz.log
x postfix-re-pkg_add.log

$ ls -l /tmp

total 1312
[snip]
-rw-r--r--  1 root  wheel     264919 Dec 25 03:36 mailman-port.log
-rw-r--r--  1 root  wheel     917943 Dec 23 23:43 pkgadd.log
-rw-r--r--  1 root  wheel      30240 Dec 24 01:10 postfix-postfix-2.5.9,2.tbz.log
-rw-r--r--  1 root  wheel      55429 Dec 24 00:13 postfix-re-pkg_add.log
Click to expand...

Thx, it works well!
Code: 
# tar xvzf ramdisk.dat -C /tmp

# ls -l /tmp
total 24
drwxr-xr-x  2 root  <<<<<<< current   1024 Aug 15  2007 bin
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 dev
drwxr-xr-x  7 root  <<<<<<< current    512 Aug 15  2007 etc
-rwxr-xr-x  1 root  <<<<<<< current    272 Aug 14  2007 init
drwxr-xr-x  3 root  <<<<<<< current   2048 Aug 15  2007 lib
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 mnt
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 proc
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 sbin
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 sys
drwxrwxr-x  2 root  <<<<<<< current    512 Aug 15  2007 tmp
drwxr-xr-x  3 root  <<<<<<< current    512 Aug 15  2007 usr
drwxr-xr-x  2 root  <<<<<<< current    512 Aug 15  2007 var
 
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