Making sure script is running in bash!

kalleanka · 02-15-2011, 07:05 AM

is this a good way of doing it? Shall I use & when starting the new process? Itested in bash and dash.

testbash=$(ps -e | grep $$ | grep bash)
if [ 0 = ${#testbash} ]; then
echo "new process"
bash MYPROCESSNAME
exit 0
fi

echo "It's in bash jippi"

Guttorm · 02-15-2011, 07:09 AM

I think it's better to specify it in the shebang

#!/bin/bash

Don't use

#!/bin/sh

when it's a bash script.

kalleanka · 02-15-2011, 07:55 AM

so if someone will call with sh, dash or so its up to them?

and i realize that i had to change mod for it to work.

thanks

druuna · 02-15-2011, 09:11 AM

Hi,

Quote:

Originally Posted by kalleanka

so if someone will call with sh, dash or so its up to them?

Nope. The hashbang (or shebang) tells the OS what needs to be used to execute/interpret the script that follows.

For example, if a script starts with:
#!/bin/bash - all that follows is done by bash,
#!/usr/bin/perl - all that follows is done by perl,
#!/bin/dash - all that follows is done by dash.

There are a lot more examples, but I guess you get the picture.

Also have a look here for a more comprehensive explanation: Shebang (Unix)

Hope this helps.

Guttorm · 02-15-2011, 10:59 AM

I think Kalleanka's code helps in a situation where a user is using something like ksh interactively and types "sh scriptname", instead of doing the chmod. I often do that because it's faster, but I use bash

ntubski · 02-15-2011, 11:21 AM

You could check that BASH is set:

Code:

if [ -z "$BASH" ]; then
   echo this script must be run with bash
   exit 1
fi

druuna · 02-15-2011, 11:26 AM

Hi,

Quote:

Originally Posted by ntubski

You could check that BASH is set:

Code:

if [ -z "$BASH" ]; then
   echo this script must be run with bash
   exit 1
fi

You shouldn't rely on this method, if you switch shells from bash to say csh the BASH variable is still present although you are now using csh....

See posts #8 and #11

ntubski · 02-15-2011, 06:46 PM

Quote:

Originally Posted by druuna

Hi,
You shouldn't rely on this method, if you switch shells from bash to say csh the BASH variable is still present although you are now using csh....

No, the variable is not exported:

Code:

~/tmp$ echo $BASH
/bin/bash
~/tmp$ zsh
% echo $BASH

%

druuna · 02-16-2011, 12:51 AM

Hi,

Quote:

Originally Posted by ntubski

No, the variable is not exported:

Code:

~/tmp$ echo $BASH
/bin/bash
~/tmp$ zsh
% echo $BASH

You are correct, I read BASH and was thinking SHELL variable.....

My mistake!

konsolebox · 02-16-2011, 01:50 AM

I wonder, is $BASH exportable to other shells? i.e. if bash runs ash.. will $BASH exist in the environment of ash?.. i forgot about this already.. but I think $BASH_VERSION or $BASH_VERSINFO is safe..

druuna · 02-16-2011, 01:56 AM

Hi,

Quote:

Originally Posted by konsolebox

I wonder, is $BASH exportable to other shells? i.e. bash runs ash.. will $BASH exist in the environment of ash?.. i forgot about this already.. but I think $BASH_VERSION or $BASH_VERSINFO is safe..

ntubski was correct about $BASH. $BASH_VERSION and $BASH_VERSINFO are also _not_ exported when switching shells.

konsolebox · 02-16-2011, 02:08 AM

@druuna: thanks for checking

off topic: bash 4.2 has been released last feb. 13 and i've checked the changelog.. one of its features says that a new option in declare/typeset has been added and it's '-g' .. with that option, variables can now be declared global in any scope even inside functions.. finally. and i'm the one who made this request before as well

i can finally make the final versions of Shell Script Loader with this ^_^