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guncat(1) guncat - unencrypting file concatenation guncat(1)

NAME

guncat - catenates files, unencrypting pgp encrypted sections

SYNOPSIS

guncat [OPTIONS] [file(s)]
[OPTIONS] - cf. section OPTIONS
[file(s)] - optional files to process (cf. section INPUT FILE(S))

DESCRIPTION

Guncat was designed to tackle a problem encountered with (partially) PGP encrypted files (which may exist in, e.g., mailboxes). Tools to process text-files (like grep(1), or less(1)) may be used to process those files, but those tools leave PGP encrypted sections inside such files as-is. As a consequence, browsing the `real’ contents (i.e., clear-text sections and the unencrypted content of PGP encrypted sections) of those files is difficult.

Guncat acts comparably to cat, but unencrypts encrypted sections encountered in the files processed by guncat, copying the unencrypted information to guncat’s standard output stream, which may thereupon be processed by other tools.

PGP/GPG encrypted sections are surrounded by the following markers:

-----BEGIN PGP MESSAGE-----
and
-----END PGP MESSAGE-----

When guncat encounters such sections they are processed by gpg(1). Gpg needs a passphrase to unencrypt such sections. If not already available (from gpg-agent(1)) the required passphrase is requested by guncat, whereafter it is used by gpg.

When an incorrect passphrase is entered two additional attempts to provide the correct passphrase are allowed. If the third attempt also fails, guncat terminates. Files processed by guncat may have to be repositioned. If repositioning is not supported guncat terminated with an error message.

RETURN VALUE

Guncat returns 0 to the operating system unless an error occurs (0 is also returned when the option --gpg-command is specified). 1 is returned if gpg could not decrypt an encrypted section or if guncat is started without arguments or options

INPUT FILE(S)

When no file arguments are provided input may be provided using standard input stream redirection.

When option --passphrase is specified the first line of the first file that is processed is read as the passphrase to be used. This line is ignored if gpg-agent already can provide the correct passphrase. Otherwise, when a thus specified passphrase is incorrect, guncat terminates.

Any other argument is considered a filename (path specifications are allowed) specifying a file to be processed (in sequence) by guncat.

If a file cannot be read guncat terminates with an error message.

OPTIONS

In the following overview of options single letter options, when available, are listed between parentheses following their associated long-option alternatives. Single letter options require arguments if their long option alternatives require arguments as well.
o
--gpg-command
Show the gpg command that would be used, and quit, returning 0.
o
--gpg-option=option (-m)
Add option to gpg’s call. If the option contains blanks, surround option by single or double quotes. Option gpg-option may repeatedly be specified.
o
--gpg-path=path
Path to the gpg program (default: /usr/bin/gpg)
o
--help (-h)
Basic usage information is written to the standard output stream.
o
--less=path (-l)
output is written to ’/usr/bin/less’. By default output is written to the std. output stream. This option cannot be specified when either option --pipe or option --write is specified.
o
--no-errors
When this options is specified guncat terminates gpg returns a non-zero exit value.
o
--passphrase -p
By default the passphrase is read by guncat after prompting the user to enter the passphrase. The passphrase is not echoed. If input redirection is used or if input files are specified option --passphrase can be specified to read the passphrase from the first line of the first input stream that is read by guncat. In that case the input stream’s first line is (of course) not written to the output stream. When the --passphrase option is specified and the provided password is incorrect, guncat terminates.
o
--pipe=path (-P)
Full path to a program receiving guncat’s output. By default output is written to the std. output stream. This option cannot be specified when either option --less or option --write is specified.
o
--pgp-ranges -r
the lines-ranges of complete PGP MESSAGE sections are reported. No additional output is produced.
o
--quoted-printable -q
merely decrypt PGP messages, keeping their quoted-printable content (by default quoted-printable content like ’=3D’ is converted to ascii).
o
--reduce-headers -R
When encountering mail headers (starting at lines beginning with `From ’ and ending at the next empty line) only output the mail headers Cc:, Date:, From:, Subject:, and To:.
o
--section-lines -S
In the output precede decrypted PGP MESSAGE sections by their line numbers, using a format like
****************************
filename:43:104: PGP MESSAGE
****************************
    
    
where the first number refers to the first line number of the PGP section and the second number refers to last line number of the PGP section
o
--skip-incomplete -s
Incomple PGP MESSAGE sections are ignored and are not outputted. By default the program’s output also contain the lines of any incomplete PGP MESSAGE sections that were encountered.
o
--time-limit=seconds (-T)
Option --time-limit is used to specify the max. time in seconds that gpg is allowed to run while decrypting a single encrypted section. By default no time limit is used. This option is useful when the file to process might contain errors in encrypted sections (like a missing END PGP MESSAGE line).
o
--tty-OK -t
Option --no-tty is not specified when calling gpg. By default it is specified.
o
--verbose=path (-V)
Path to where guncat should write additional messages. Specify - to write the messages to the standard error stream.
o
--version (-v)
Guncat’s version number is written to the standard output stream, terminating guncat, returning exit value 0.
o
--write=path (-W)
output is written to path. If path already exists gpg terminates. By default output is written to the std. output stream. This option cannot be specified when either option --less or option --pipe is specified.

SEE ALSO

gpg(1), gpg-agent(1), grep(1), less(1).

BUGS

None reported

COPYRIGHT

This is free software, distributed under the terms of the `GNU General Public License’. Copyright remains with the author. Guncat is available at https://fbb-git.gitlab.io/guncat/

AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).
2014-2020 guncat_2.00.01