Connecting Filters with Redirection and Piping
Connecting Filters with Redirection and Piping
Piping
the standard output from the first command is
sent to the second command as standard input
before it goes to the output device
% who | more
% cat file1 | more == % more file1
% sort file1 | uniq | more
% who | grep jp107 | sort | uniq | more
-------------------------------------------
Redirection of Standard Input
allows you to send the contents of a text file
into a utility that expects standard input
% mail jplane < file.ltr
% mail -s "subject line" jplane < file.ltr
-------------------------------------------
Redirection of Standard Output
allows you to capture the standard output of a
command into a file for use later by creating a
new file or replacing the contents of a file
that already exists
% who > who.list
% man vi > man.file
-------------------------------------------
Redirection of Standard Output to Append
allows you to capture the standard output of a
command into a file that already exists allows
you to append the standard output of a command
to the end of a file that already exists or to
create the file if it does not
% man learn >> man.file
Example with cat
% cat > this
creates the file getting info from
standard input end with ^D
% cat this
displays the contents to standard output
% cat > that
creates the file getting info from
standard input end with ^D
% cat < that
displays the contents to standard output
(same as % cat that)
% cat this that > other
creates the file named other with the
contents from both this and that
% cat other
displays the contents to standard output
% cat this >> other
adds another copy of this to the contents
of the file named other
% cat other
displays the contents to standard output
-------------------------------------------
tee filter
redirection into a file, but a copy also
continues down the standard input stream
utility producing output------------,----------->
to standard output |
|
v
file
Examples
% who | tee who.list
% who | tee who.1 | more
% who | tee who.1 > who.2
Have the same results:
% cat f1 | tee f2
% cp f1 f2
% cat f1
%cat f1 > f2
%cat f1
bigger example:
% cat f1 | tee f2 | tee f3 | tee f4 > f5
here document
redirection within a script
cat Working dir $PWD
> EOF
Working dir /home/user
------------------
noclobber shell variable
if it is turned on, it
will prevent overwriting a file when you use
the redirection of standard output
and it will prevent creating a file when you
use the appending redirection the ! addition
allows you to override the protection when
noclobber is turned on
commands:
% set noclobber
% unset noclobber
Examples:
% set noclobber % set noclobber
% cat this > that % cat this >> new.file
error error
% cat this >! that % cat this >>! new.file
% unset noclobber % unset noclobber
% cat this > that % cat this >> newer.file
Redirection of STDERR
“some command “ &2>1
“some command” &2>/dev/null
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