Execute second command only if first fails/succeeds?

I am not sure about on how to specify that a second command should only be execute in case
that the first commnd fails/succeeds.

When I enter:

cmd1 | gzip -f ... && cmd2

Is then cmd2 executed only if cmd1 is finished successfully or if gzip is finished successfully?

What if I want cmd2 only to execute if both (cmd1 and gzip) end successfully?

What about the other way: cmd2 should only be executed if

a) cmd1 failed

b) cmd1 or gzip failed?

Matthew

2008-06-14, 08:28(+00), Matthew Lincoln:
> I am not sure about on how to specify that a second command should only be execute in case
> that the first commnd fails/succeeds.
>
> When I enter:
>
> cmd1 | gzip -f ... && cmd2
>
> Is then cmd2 executed only if cmd1 is finished successfully or if gzip is finished successfully?
>
> What if I want cmd2 only to execute if both (cmd1 and gzip) end successfully?
>
> What about the other way: cmd2 should only be executed if
>
> a) cmd1 failed
>
> b) cmd1 or gzip failed?
[...]

With the zsh shell:

setopt extendedglob

cmd1 | gzip
(( ${pipestatus[(I)^0]} )) || cmd2

Or:

cmd1 | gzip

(( $pipestatus[1] || $pipestatus[2] )) || cmd2

See question 11 in comp.unix.shell FAQ:

http://cfaj.freeshell.org/shell/cus-faq-2.html#11

for more details.

--
Stéphane

kmlincoln100@hotmail.com (Matthew Lincoln) writes:

>I am not sure about on how to specify that a second command should only be execute in case
>that the first commnd fails/succeeds.

>When I enter:

>cmd1 | gzip -f ... && cmd2

>Is then cmd2 executed only if cmd1 is finished successfully or if gzip is finished successfully?

No. They go in order. the && will apply to gzip. BUt if cmd1 fails, the
pipe is broken and gzip fails anyway.

>What if I want cmd2 only to execute if both (cmd1 and gzip) end successfully?

>What about the other way: cmd2 should only be executed if

>a) cmd1 failed

>b) cmd1 or gzip failed?

man bash

On Sat, 14 Jun 2008 14:22:20 +0000, Unruh wrote:

> kmlincoln100@hotmail.com (Matthew Lincoln) writes:
>
>>I am not sure about on how to specify that a second command should only
>>be execute in case that the first commnd fails/succeeds.
>
>>When I enter:
>
>>cmd1 | gzip -f ... && cmd2
>
>>Is then cmd2 executed only if cmd1 is finished successfully or if gzip
>>is finished successfully?
>
> No. They go in order. the && will apply to gzip. BUt if cmd1 fails, the
> pipe is broken and gzip fails anyway.
>
>>What if I want cmd2 only to execute if both (cmd1 and gzip) end
>>successfully?
>
>>What about the other way: cmd2 should only be executed if
>
>>a) cmd1 failed
>
>>b) cmd1 or gzip failed?
>
> man bash

The exit status of a pipeline in bash is the exit status of the last
command in the pipeline - but you can use set -o pipefail to make it
error for any command in the pipeline, not just the last.