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 Forum index » Off-Topic Area » Programming
Bash question [Solved]
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zigbert


Joined: 29 Mar 2006
Posts: 6629
Location: Valåmoen, Norway
PostPosted: Thu 07 Jun 2012, 18:10    Post subject:  Bash question [Solved]
Subject description: I don't want terminal output		  
This small example shows how I often make tests in my scripts
Code:
#!/bin/bash
echo true > /tmp/test1
[ "$(</tmp/test2)" = "true" ] && echo true
As you see, the file test2 won't hold 'true', and bash gives the annoying terminal output:
Code:
line 3: /tmp/test2: No such file or directory
Sure it's true there is no file, but I don't won't to see the message.



For variable content it is enough to use qoutes to skip message.
Code:
[ "$TEST" = "true" ] && echo true
For content of files I can use cat and send errors to /dev/null
Code:
[ "`cat /tmp/test2 2> /dev/null`" = "true" ] && echo true
But in the end I would like to use bash.... and can't find the correct syntax.
I know some of you know it Wink


Thank you
Sigmund
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Last edited by zigbert on Sat 09 Jun 2012, 01:05; edited 1 time in total
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sunburnt


Joined: 08 Jun 2005
Posts: 5089
Location: Arizona, U.S.A.
PostPosted: Thu 07 Jun 2012, 18:34    Post subject:  
Hi zigbert; I assume that you want just this error removed?
" No such file or directory "

I was going to suggest grep, but I understand what you`re looking for.
Lit me see what I can find... Terry
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Karl Godt


Joined: 20 Jun 2010
Posts: 4208
Location: Kiel,Germany
PostPosted: Thu 07 Jun 2012, 19:15    Post subject:  
Code:
[ -f /tmp/test1 ] && { [ "$(</tmp/test2)" = "true" ] && echo true; }

OR

Code:
exec 2>/dev/null;[ "$(</tmp/test2)" = "true" ] && echo true;exec 2>/dev/stderr


would come into mind

Note : exec 2>/dev/null works in script but not in rxvt as in /etc/rc.d/rc.shutdown
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sunburnt


Joined: 08 Jun 2005
Posts: 5089
Location: Arizona, U.S.A.
PostPosted: Thu 07 Jun 2012, 23:37    Post subject:  
I tried all sorts of Bashisms, but they all failed to quell the error output.

Here`s the best idea I came up with:
Code:
sh-4.1# [ -e /tmp/test1 ]&& echo $(</tmp/test1)
true
sh-4.1# [ -e /tmp/test2 ]&& echo $(</tmp/test2)
sh-4.1#

Last edited by sunburnt on Fri 08 Jun 2012, 15:42; edited 1 time in total
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Bruce B

Joined: 18 May 2005
Posts: 11488
Location: The Peoples Republic of California
PostPosted: Fri 08 Jun 2012, 02:05    Post subject:  
I think this is what I used to supress terminal output


command &>/dev/null


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amigo

Joined: 02 Apr 2007
Posts: 2647
PostPosted: Fri 08 Jun 2012, 02:18    Post subject:  
'1> /dev/null' quietens normal output. '2> /dev/null' quietens error output. '&> /dev/null' quietens them both.
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jamesbond

Joined: 26 Feb 2007
Posts: 3475
Location: The Blue Marble
PostPosted: Fri 08 Jun 2012, 08:25    Post subject: Re: Bash question
Subject description: I don't want terminal output		  
This seems to do the trick
Code:
#!/bin/bash
echo true > /tmp/test1
exec 2> /dev/null
[ "$(</tmp/test2)" = "true" ] && echo true


But note that you will lose all errors after the exec line (ie all errors goes to /dev/null) after that.
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jamesbond

Joined: 26 Feb 2007
Posts: 3475
Location: The Blue Marble
PostPosted: Fri 08 Jun 2012, 08:33    Post subject:  
Surprisingly, in bash at least, in UTF-8 locale at least (that's my test environment), testing for presence for file first before reading it is faster than blindly read the file and suppress the error.

This code:
Code:
#!/bin/bash

func1() {
   2> /dev/null read p < /etc/xxx
}

func2() {
   [ -e /etc/xxx ] && read p < /etc/xxx
}


p=5
echo -n func1
time for a in $(seq 1 10000); do func1; done
echo

echo -n func2
time for a in $(seq 1 10000); do func2; done
echo
echo p is $p

exec 2> /dev/null
[ "$(</etc/passwd)" ] && echo passwd there
[ "$(</etc/passwdxxx)" ] && echo passwdxxx there


gives this surprising results:
Code:
func1
real   0m0.331s
user   0m0.270s
sys   0m0.057s

func2
real   0m0.155s
user   0m0.137s
sys   0m0.017s

p is 5
passwd there

I have always been under the impression that the "test" commands are slow and to be avoided (use "case" instead), but apparently it is not so slow after all ... benchmark is king isn't it Embarassed
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sunburnt


Joined: 08 Jun 2005
Posts: 5089
Location: Arizona, U.S.A.
PostPosted: Fri 08 Jun 2012, 15:47    Post subject:  
jamesbond; Yep, it`s surprising what you find, like Bash takes 0ms.

Like tests on copying an SFS file`s contents showed it`s faster than
copying the loose files on the partition. That`s just sooo weird...
Try it some time!
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zigbert


Joined: 29 Mar 2006
Posts: 6629
Location: Valåmoen, Norway
PostPosted: Sat 09 Jun 2012, 01:04    Post subject:  
Thank you for all feedback
I didn't realize that I could chain several tests. This works
Code:
#!/bin/bash
echo true > /tmp/test1
[ -e /tmp/test2 ] && [ "$(</tmp/test2)" = "true" ] && echo true


Sigmund
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sunburnt


Joined: 08 Jun 2005
Posts: 5089
Location: Arizona, U.S.A.
PostPosted: Sun 10 Jun 2012, 00:09    Post subject:  
.
Glad to see the community coming together for a good cause...
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