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https://github.com/j256/null
Unix command line utility which combines /dev/null, tree, md5sum, and other useful features.
https://github.com/j256/null
command-line-tool devnull md5sum tee unix unix-command
Last synced: about 1 month ago
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Unix command line utility which combines /dev/null, tree, md5sum, and other useful features.
- Host: GitHub
- URL: https://github.com/j256/null
- Owner: j256
- License: isc
- Created: 2020-03-09T00:10:18.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2024-07-11T16:00:14.000Z (4 months ago)
- Last Synced: 2024-07-11T18:26:54.213Z (4 months ago)
- Topics: command-line-tool, devnull, md5sum, tee, unix, unix-command
- Language: C
- Homepage:
- Size: 227 KB
- Stars: 1
- Watchers: 3
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: ChangeLog
- Funding: .github/FUNDING.yml
- License: LICENSE.txt
Awesome Lists containing this project
README
Null Utility
============
[](https://github.com/j256/null/blob/master/src/main/javadoc/doc-files/changelog.txt)
[](https://circleci.com/gh/j256/null)
[](https://github.com/j256/null/blob/master/LICENSE.txt)
## Documentation
Sorry for the limited documentation here. Basically null is a
combination of /dev/null, tee, md5sum, with the addition of some other
features.
## Arguments
Here are more details on some of the less obvious flags.
* [-d size] or --dot-blocks show a dot each X bytes of input
With this size, you can have null output a period ('.') to standard
error for every X bytes read in. You can specify the size as 20k or
100m.
* [-f output-file] or --output-file output file(s) to write input
You can write any input bytes into an output file by using this
option. To handle multiple files, specify multiple -f options.
* [-F] or --flush-output flush output to files
This will cause null to call fflush on each of the output streams
after it writes to them.
* [-m] or --md5 run input bytes through md5
This will display the md5 signature for the input data. If you are
transporting data across a stream, it is useful to use the -r and -w
options. See below.
* [-n] or --non-block don't block on input
Set the input file-descriptor to be non-blocking. Not sure if this
really accomplishes anything.
* [-p] or --pass-input pass input data to output
This will write the input to the standard output.
* [-r] or --read-pagination read pagination data
Null can add basic pagination information into the stream. Network
transmissions often block the input and output to fixed sizes and add
`\0` characters at the end as padding. With pagination, these
extraneous characters will be removed and so MD5 calculations (with
-m) will be valid. This should be used to read the output of null
with a -w flag specified.
* [-t size] or --throttle-size throttle output to X bytes / sec
This will throttle the output of null to a specific size (10k or 1m)
per second. This is useful if you don't want to overflow a network
connection for instance.
* [-w] or --write-pagination write paginate data
Like -r but this should be used to write output to a null with a -r
flag specified.
## Examples
To write output to multiple log files:
tar -cvzf - /usr | \
null -f /backup/usr.tar.gz -f /backup2/usr.tar.gz
To transmit some files between two systems with pagination and while
reporting the md5 signature of the data. On the remote host:
nc -l -p 5000 | null -r -p -m | tar -xf -
On the local host:
tar -cf - . | null -w -p -m | nc remote-hostname 5000
To see a dot ('.') for every megabyte of byte we are getting out of
our backup program.
tar -cf - . | null -d 1m -p -f /dev/nrst0
To limit the transfer of a hierarchy to a remote system to 100kB/sec
and print a dot for every 10kB.
tar -cf - . | null -d 10k -t 100k -p | nc remote-hostname 5000
## Repository
The newest versions of the library are available via: https://github.com/j256/null
Enjoy. Gray Watson