Arch Linux

tony5429

Member

Registered: 2006-03-28

Posts: 1,017

Very simple question about linux command line

Can anyone explain this? Why is the variable only saved if it is done on two different lines? And how can I save the variable and echo it in the same line??

[karam@vladimir ~]$ x="hi" | echo $x

[karam@vladimir ~]$ x="hi"
[karam@vladimir ~]$ echo $x
hi

I apologise in advance for being a bit of a noob; I'm sure the issue is something simple.

skottish

Forum Fellow

From: Here

Registered: 2006-06-16

Posts: 7,942

Re: Very simple question about linux command line

Try this:

x="hi" && echo $x

You piped no output to echo in your first example.

Last edited by skottish (2008-03-15 04:14:10)

valnour

Member

From: Cleveland, TN, USA

Registered: 2008-02-17

Posts: 84

Website

Re: Very simple question about linux command line

It works fine for me with zsh, I'm assuming you are using bash. Your problem could be related to your use of a pipe. You probably want two ampersands (&&).

Last edited by valnour (2008-03-15 04:14:21)

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tam1138

Member

Registered: 2007-09-10

Posts: 238

Re: Very simple question about linux command line

This command

x="hi" | echo $x

causes the shell to start two different processes and then hook them together via a pipe.  They are otherwise unrelated, so changes to the environment of the first (which is what x="hi" is doing) does not affect the environment of the second.  In contrast, this command:

x="hi" && echo $x

causes the shell to run the first command and then run the second if and only if the first succeeded, but in the same process, and therefore the same environment.

peart

Member

From: Kanuckistan

Registered: 2003-07-28

Posts: 510

Re: Very simple question about linux command line

You could also separate both commands with a ;.  Whichever works for you...

tony5429

Member

Registered: 2006-03-28

Posts: 1,017

Re: Very simple question about linux command line

Wow! Thanks for the help. I am using the && and it works for me now One more question, I actually need an if-then statement on one line... but this is not working...

x = "hi" && if [ ! -z "${x:16}" ] then echo "${x::16}..." else echo $x

Does anyone know how to correctly do it?

Snowman

Developer/Forum Fellow

From: Montreal, Canada

Registered: 2004-08-20

Posts: 5,212

Re: Very simple question about linux command line

you're missing a semi-colon after the test and forgot to end the if statement with fi

x = "hi" && if [ ! -z "${x:16}" ] ;then echo "${x::16}..." else echo $x ;fi

tony5429

Member

Registered: 2006-03-28

Posts: 1,017

Re: Very simple question about linux command line

Hrm... I must be missing something else too...

[karam@vladimir ~]$ x="hi" && if [ ! -z "${x:16}" ] ;then echo "${x::16}..." else echo $x ;fi
[karam@vladimir ~]$

Shouldn't it output "hi"?

peart

Member

From: Kanuckistan

Registered: 2003-07-28

Posts: 510

Re: Very simple question about linux command line

[marc@~] x="hi" && if [ ! -z "${x:16}" ]; then echo "${x::16}"; else echo "$x"; fi
hi
[marc@~] x="supercalafragilistic" && if [ ! -z "${x:16}" ]; then echo "${x::16}"; else echo "$x"; fi
supercalafragili
[marc@~]

tony5429

Member

Registered: 2006-03-28

Posts: 1,017

Re: Very simple question about linux command line

Thanks, Peart!!