Re^3: using a pipe

OK, so if I understand correctly,

The passphrase comes from file
The input (ciphertext) is in a file and gpg is given this file on its command line, and
The output goes into another file, again directed by a command line option.

The first thing to notice is that the cat might be unnecesary. In other words,

cat file | gpg
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should have the same effect as

gpg <file
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but the second is simpler and eliminates an unnecesary pipeline stage. In either case the contents of file becomes the standard input for gpg. The only reason it would matter is if for some reason gpg really insisted that the passphrase-fd be a pipe.

If that will do, then you may be able to reduce the whole thing down to something as simple as this:

# Open the file
open(FILE, "<file") || die;

# Run gpg
# Notice that we are not going to bother to try to
# make the file become stdin to gpg. We're just going
# to tell gpg which file descriptor it's already
# accessible as.
system("gpg", "--passphrase-fd=" . fileno(FILE),
    "--decrypt", "--output", "cleartext-filename",
    "ciphertext-filename");

close FILE;
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That's the true intent of gpg's passphrase-fd option: to give it a file descriptor for some other file besides the three stdio ones.

You may notice that this can be improved a little bit because, in fact, the parent process (perl script) does not have to open the file at all, it only needs to be opened in the child process (the one that execs gpg). You can easily make that change to the above example but you have to play with fork, exec and waitpid in order to do so, and it does not seem worthwhile to me to do so since it does no harm to open the file in the parent process.

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Re^4: using a pipe
by drock (Beadle) on Dec 30, 2005 at 19:48 UTC

C:\Program Files\GNU\GnuPG>gpg --passphrase-fd=ohiohea1th_is --decrypt
+ --output decrypted.txt tstfil
e.asc
Reading passphrase from file descriptor 0 ...


You need a passphrase to unlock the secret key for
user: "derek smith"
2048-bit ELG-E key, ID 985DB557, created 2005-12-30 (main key ID 4A673
+EF3)

gpg: encrypted with 2048-bit ELG-E key, ID 985DB557, created 2005-12-3
+0
      "derek smith"
gpg: public key decryption failed: bad passphrase
gpg: decryption failed: secret key not available
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--passphrase-fd=
open (PASS, "+<$pass")
using . fileno(PASS)
I get this error:
Reading passphrase from file descriptor 3 ...


You need a passphrase to unlock the secret key for
user: "derek smith"
2048-bit ELG-E key, ID 985DB557, created 2005-12-30 (main key ID 4A673
+EF3)

gpg: encrypted with 2048-bit ELG-E key, ID 985DB557, created 2005-12-3
+0
      "derek smith"
gpg: public key decryption failed: bad passphrase
gpg: decryption failed: secret key not available
Press any key to continue . . .
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C:\Program Files\GNU\GnuPG>echo ohiohea1th_is|gpg --passphrase-fd=0 --
+decrypt --output decrypted.txt
 tstfile.asc
Reading passphrase from file descriptor 0

You need a passphrase to unlock the secret key for
user: "derek smith"
2048-bit ELG-E key, ID 985DB557, created 2005-12-30 (main key ID 4A673
+EF3)

gpg: encrypted with 2048-bit ELG-E key, ID 985DB557, created 2005-12-3
+0
      "derek smith"

C:\Program Files\GNU\GnuPG>dir
 Volume in drive C is IBM_PRELOAD
 Volume Serial Number is 2863-8FD9

 Directory of C:\Program Files\GNU\GnuPG

12/30/2005  02:49 PM    <DIR>          .
12/30/2005  02:49 PM    <DIR>          ..
12/30/2005  02:49 PM                15 decrypted.txt
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