From: ara.t.howard@...
Date: 2006-09-29T01:09:09+09:00
Subject: Re: how to determine if pipe is given

On Fri, 29 Sep 2006 gwtmp01@mac.com wrote:

> In both cases if you leave off the '-' the program will report an error
> rather than reading and processing the data.  The next programmer
> who comes along is going to be very confused by this behavior.

not if they work on unix!  ;-)

> Can anyone think of a standard Unix program that will *only* read from
> stdin in if you give an explicit sentinel as a file argument?


#
# tarfile on stdout
#
harp:~ > tar -cf - directory  > tarfile_on_stdout.tgz

#
# piped tarfile on stdin
#
harp:~ > tar -cf - directory | tar -xvf -


#
# copying files overnetwork via piped tarfile and unpacking on the other side
#
harp:~ > (cd /src; tar -cvf - foo) | (ssh other.machine 'cd /dst; tar -xf -')


#
# echo foobar into a gzip of stdin, sending compressed output to stdout, pipe
# that into another gzip which is decompressing stdin, dump that output back
# out to stdout
#
harp:~ > echo foobar | gzip - -c | gzip -d - -c
foobar

#
# use image magick's convert command to convert stdin -> stdout
#
harp :~ > convert - - < map.png > map2.png
harp :~ > file map2.png
map2.png: PNG image data, 713 x 569, 8-bit/color RGB, non-interlaced

#
# grep for list of patterns on stdin
#
harp:~ > echo alias | grep -f- .bashrc
   alias new='ls -ltar'
   alias p="fetchmail;pine -i -passfile /home/ahoward/.passfile"
   alias g="glimpse -n -H"
   alias gi='glimpseindex -B -t -f -H'
   alias ldate='env TZ=America/Denver date'
   alias ssh='ssh -X'
   alias vi='vim'
   alias mussel='tti -A nrt@mussel.ngdc.noaa.gov'
   alias ss='screen -S '
   alias sl='screen -list '
   alias sdr='screen -d -r '
   alias s='screen -D -R '
   alias dark='eval `dircolors /etc/DIR_COLORS` && export DIR_COLORS=dark'
   alias light='eval `dircolors /etc/DIR_COLORS.xterm` && export DIR_COLORS=light'
   alias xt="xterm -font 7x13 -fb 7x13B -geometry 80x25 -sb -wf -j -ls  -bg Black -fg grey &"



note that none of these are documented.  i think that's because it's considered
'standard' bahaviour.


cheers.


-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei