Linux .... bash-v what is it?

casperdaghost · 01-05-2012, 11:03 AM

I have been apending the pipe bash -v to the end of my scripts. It seems to pipe whatever is printed out by the command into an executable something.
I am not sure how it works or what it is - looked on the interwebs adn man pages and could not find a thing.

It is a great tool

Code:

casper@casperbox:~$ ps auxwww   | grep chrome | awk '{print "kill -9 "$2}'| bash -v
kill -9 1235
bash: line 1: kill: (1235) - No such process
kill -9 10633
kill -9 13854
kill -9 20354
kill -9 20358
kill -9 20360
kill -9 20362
kill -9 20886
kill -9 23051
kill -9 23144
kill -9 23302
kill -9 28158
kill -9 29787
kill -9 29878
kill -9 30145
kill -9 31524

corp769 · 01-05-2012, 11:11 AM

Hello,

The -v just means verbose; Using "bash -v," it will print each command to STDOUT before executing the command(s). For a reference/manual, see here - http://tldp.org/LDP/abs/html/options.html

Cheers,

Josh

casperdaghost · 01-05-2012, 06:08 PM

thank you for the refreence - piping commands into a bash -v is a kick a$$ feature.

chrism01 · 01-05-2012, 06:22 PM

Actually, that will invoke a new instance/shell of bash.
If you want to see what's going on in a current script, use

Code:

set -v

#OR
#more detail
set -xv

inside your script

corp769 · 01-05-2012, 06:56 PM

Quote:

Originally Posted by chrism01

Actually, that will invoke a new instance/shell of bash.
If you want to see what's going on in a current script, use

Code:

set -v

#OR
#more detail
set -xv

inside your script

Hmmm.... So I'm wrong? I thought it was strictly for verbose mode.

chrism01 · 01-05-2012, 07:08 PM

Yeah, '-v' =verbose, but 'bash' is still a cmd that invokes a new (sub-)shell.
Because its at the end of a pipe (in this instance) you don't notice it

corp769 · 01-05-2012, 07:17 PM

Oh I did! I was just confused on your context and wording of how you said that. All is good!

Cheers,

Josh

chrism01 · 01-05-2012, 11:04 PM

Ah, ok sorry about the confusion. I was trying to say to the OP that you can use that switch inside a script, rather than invoking a new sub-shell

corp769 · 01-06-2012, 12:17 AM

Oh ok, I understand now.

casperdaghost · 01-07-2012, 05:05 PM

what would i use if i did not want the executed commands to out put to the console -

corp769 · 01-07-2012, 05:22 PM

Just take away the -v out of the snippet of code. Alternatively, you could run the following:

Code:

code 1>/dev/null 2>/dev/null

Cheers,

Josh

David the H. · 01-07-2012, 07:43 PM

To disable an option with set change the minus to a plus.

Code:

set -v	#enable verbosity
set +v	#disable verbosity

This, along with the -x option, is particularly useful in scripts for debugging.

Note that most of the set options correspond to options you can use when invoking bash directly. "bash -v" runs an instance of bash with verbosity enabled (you can add it to the shebang at the top of a script, for example). Or you can run bash with no options first, then use set -v separately to do the same thing.

And as always, the details are in the man page. Start with the OPTIONS section at the top, then scroll down to the SHELL BUILTIN COMMANDS and read the entry for set.