3 May
2017
3 May
'17
6:52 a.m.
With Steve's eloquent grump and cat -v on the table, I can't
help re-citing the peerless cardinal sin of
less --help | wc
Doug
3 May
3 May
6:59 a.m.
New subject: dmr note on BSD's sins
On Tue, 2 May 2017, Doug McIlroy wrote:
With Steve's eloquent grump and cat -v on the
table, I can't help
re-citing the peerless cardinal sin of
less --help | wc
Speaking of "cat", what really drives me nuts is "cat file | cmd"...
What's wrong with "cmd < file" (or to really confuse newbies, "<
file
cmd")?
--
Dave Horsfall DTM (VK2KFU) "Those who don't understand security will
suffer."
6:54 p.m.
New subject: dmr note on BSD's sins
On Tue, May 2, 2017 at 8:59 PM, Dave Horsfall <dave(a)horsfall.org> wrote:
On Tue, 2 May 2017, Doug McIlroy wrote:
Ooo! Ooo! Ooo! I've actually got something for this....
First of all, there's nothing strictly speaking *wrong* with 'cmd <
file'
and cat 'cat file | cmd' is definitely overused, often unintentionally and
out of ignorance.
However, 'cmd <file' requires 'file' as a literal string in the
command;
`cat` can be useful when the file parameter may be optional. E.g., 'cat
"$@" | ...'. Now some folks will immediately respond by saying, "many
commands will read from stdin if a filename is not presented on the command
line, so why not, 'cmd "$@"'?" And that's certainly a valid
question, to
which I would answer that the semantics of a command sometimes subtly
change when presented with one or more filenames as argument (e.g. 'grep'),
so using `cat` may suppress that behavior if desired. "But `grep` has the
`-h` option to tell it not to print the filename!" Yes, but `grep` is just
*one command* and not *all* of them do. The point being that 'cat' in a
pipeline has it's place, even if that place is rarely the place we see it.
Another, related use to cover up one of the more odious of recent design
decisions in Unix-like systems is to use `cat` at the *end* of the
pipeline. Some programs change behavior if they know that they are writing
into a tty; one can suppress that if one terminates the pipeline in `cat`.
This is surely a case of mis-using a feature to mask a bug, but it's often
useful regardless.
- Dan C.
With Steve's eloquent grump and cat -v on
the table, I can't help
re-citing the peerless cardinal sin of
less --help | wc
Speaking of "cat", what really drives me nuts is "cat file | cmd"...
What's wrong with "cmd < file" (or to really confuse newbies,
"< file
cmd")? 
7:09 p.m.
New subject: dmr note on BSD's sins
Not to mention, you can cat multiple files - as in concatenate :)
On 5/3/2017 8:54 AM, Dan Cross wrote:
On Tue, May 2, 2017 at 8:59 PM, Dave Horsfall
<dave(a)horsfall.org
<mailto:dave@horsfall.org>> wrote:
On Tue, 2 May 2017, Doug McIlroy wrote:
With Steve's eloquent grump and cat -v on
the table, I can't help
re-citing the peerless cardinal sin of
less --help | wc
Speaking of "cat", what really drives me nuts is "cat file |
cmd"...
What's wrong with "cmd < file" (or to really confuse newbies,
"< file
cmd")?
Ooo! Ooo! Ooo! I've actually got something for this....
First of all, there's nothing strictly speaking *wrong* with 'cmd <
file' and cat 'cat file | cmd' is definitely overused, often
unintentionally and out of ignorance.
However, 'cmd <file' requires 'file' as a literal string in the
command; `cat` can be useful when the file parameter may be optional.
E.g., 'cat "$@" | ...'. Now some folks will immediately respond by
saying, "many commands will read from stdin if a filename is not
presented on the command line, so why not, 'cmd "$@"'?" And
that's
certainly a valid question, to which I would answer that the semantics
of a command sometimes subtly change when presented with one or more
filenames as argument (e.g. 'grep'), so using `cat` may suppress that
behavior if desired. "But `grep` has the `-h` option to tell it not to
print the filename!" Yes, but `grep` is just *one command* and not
*all* of them do. The point being that 'cat' in a pipeline has it's
place, even if that place is rarely the place we see it.
Another, related use to cover up one of the more odious of recent
design decisions in Unix-like systems is to use `cat` at the *end* of
the pipeline. Some programs change behavior if they know that they are
writing into a tty; one can suppress that if one terminates the
pipeline in `cat`. This is surely a case of mis-using a feature to
mask a bug, but it's often useful regardless.
- Dan C.
7:46 p.m.
New subject: dmr note on BSD's sins
On 3 May 2017 10:59 +1000, from dave(a)horsfall.org (Dave Horsfall):
What's wrong with "cmd < file" (or
to really confuse newbies, "< file
cmd")?
If you want to _really_ confuse a newbie, stick an "<file" or
">file"
_in the middle of_ a long command, and watch hilarity ensue.
Or the "<sth>" that someone here mentioned, if you are so inclined...
--
Michael Kjörling • https://michael.kjorling.se • michael(a)kjorling.se
“People who think they know everything really annoy
those of us who know we don’t.” (Bjarne Stroustrup)
8:57 p.m.
New subject: dmr note on BSD's sins
below...
On Tue, May 2, 2017 at 8:59 PM, Dave Horsfall <dave(a)horsfall.org> wrote:
On Tue, 2 May 2017, Doug McIlroy wrote:
To Doug -- touché
With Steve's eloquent grump and cat -v on
the table, I can't help
re-citing the peerless cardinal sin of
less --help | wc
Speaking of "cat", what really drives me
nuts is "cat file | cmd"...
What's wrong with "cmd < file" (or to really confuse newbies,
"< file
cmd")?
Not to be argumentative, but Dave, please be careful. I agree that
idiom is misused, but there are times when I think it is appropriate, which
is one of the reason why I love the Unix guiding principle of not "forcing"
the user to do one thing or another because we know better, but letting
education and good 'taste' be the guide.
I think Justice Potter Stewart described pornography of knowing it when
he sees it. IMO: there are time when using cat is in better taste that a
file redirection. For instance, I can think of a few examples when I need
to direct input from multiple files, using a more complex 'wye' style pipe
line or a redirection from backward quotes, that the cat foo sequence seems
like its easier to understand/debug. [Maybe it shows my inner
schizophrenia and heard voices from multiple places that I kinda like the
'wye' command].
Clem
9:44 p.m.
New subject: dmr note on BSD's sins
Early line at time version of paste
On Wed, May 3, 2017 at 11:34 AM, <arnold(a)skeeve.com> wrote:
[Maybe it
shows my inner
schizophrenia and heard voices from multiple places that I kinda like the
'wye' command].
Um, what is the 'wye' command? Never heard of it...
Thanks,
Arnold
2790
days inactive
2790
days old
7 comments
7 participants
participants (7)
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arnold＠skeeve.com -
Arthur Krewat -
Clem Cole -
Dan Cross -
Dave Horsfall -
Doug McIlroy -
Michael Kjörling