[TUHS] dmr note on BSD's sins

Arthur Krewat krewat at kilonet.net
Wed May 3 23:09:52 AEST 2017


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 at horsfall.org 
> <mailto:dave at 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.
>



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