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Top Forums Shell Programming and Scripting tcsh - understanding difference between "echo string" and "echo string > /dev/stdout" Post 302668551 by marcink on Monday 9th of July 2012 11:01:34 AM
Old 07-09-2012
tcsh - understanding difference between "echo string" and "echo string > /dev/stdout"

I came across and unexpected behavior with redirections in tcsh. I know, csh is not best for redirections, but I'd like to understand what is happening here.

I have following script (called out_to_streams.csh):
Code:
#!/bin/tcsh -f

echo Redirected to STDOUT > /dev/stdout
echo Redirected to STDERR > /dev/stderr

echo Should default to STDOUT without redirection

When I pipe the output like this:
Code:
./out_to_streams.csh | vim -

I get "Redirect to STDOUT" and "Should default to STDOUT without redirection" being piped.

When I redirect to a file:
Code:
./out_to_streams.csh > mystdout

  • the shell shows "Redirected to STDERR" as expected
  • mystdout only contains "Should default to STDOUT without redirection"
  • "Redirected to STDOUT" is totally missing
Anyone can explain what happens to "Redirected to STDOUT"?
 

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echo(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME
echo - echo arguments to standard output SYNOPSIS
/usr/ucb/echo [-n] [argument] DESCRIPTION
echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output. echo is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi- ronment variables. For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows: o echo your current-working-directory's full pathname o pipe the output through tr to translate the path's embedded slash-characters into space-characters o pipe that output through wc -w for a count of the names in your path. example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w" See tr(1) and wc(1) for their functionality. The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be invoked if the user calls echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the black-slashed escape characters, and ksh's echo() also understands a as the audible bell character; however, these commands do not have an -n option. OPTIONS
-n Do not add the NEWLINE to the output. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
csh(1), echo(1), ksh(1), sh(1), tr(1), wc(1), attributes(5) NOTES
The -n option is a transition aid for BSD applications, and may not be supported in future releases. SunOS 5.10 3 Aug 1994 echo(1B)
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