Expected loop does not happens in a bash script. :shock:

[bull.backup]

Hello.
Probably this be a silly question, for this reason I'm posting it here, instead of the Bash forum.
This script instead of the loop, opens and closes the terminal screen so fast that I can not see what it did.
The script works fine if I remove the string `date "+%D %R"` from the echo command line.
Also, if I type manually the two lines of the loop in a terminal, I get the expected answer.

Any help will be fully apreciated.
Thanks in advance.
Juan

#!/bin/bash

for (( ; ; ))
do
mac=$(ifconfig wlan0 | grep HWaddr | sed 's/.*HWaddr //')
echo `date "+%D %R"`" MAC ADDRESS local es $mac"
sleep 5m
done

[xenopeek]

Moved here as this is where the other users knowing bash visit more often.

[semicolon]

I don't see any problems and it also works perfectly fine for me. What happens if you call it from a terminal?

Code: Select all

sh yourscript.sh

edit:
Should have tried that myself first It reports a syntax error as it doesn't like your for loop and I totally agree that it isn't nice.

Instead of your for loop, try something like:

Code: Select all

while true;
do
    <code>
done

Funny really as i ran your code in terminal using './yourscript.sh' and it ran perfectly fine, always believed both did the same thing but apparantly I was wrong.

[xenopeek]

I don't see any problems and it also works perfectly fine for me. What happens if you call it from a terminal?

Code: Select all

sh yourscript.sh

Perhaps try bash yourscript.sh instead; running it with sh while you are using bash syntax is not funny

[semicolon]

Perhaps try bash yourscript.sh instead; running it with sh while you are using bash syntax is not funny

Good point, usually it is no problem at all though. What happens if invoked with sh, is that bash mimics the behaviour of older versions of sh. Generally not a good habit though.

I'm more into shell than bash anyways, and... my script works in both bash and sh

To summarize: your script should work fine, if it doesn't try run it in the terminal

[cfaj]

I don't see any problems and it also works perfectly fine for me. What happens if you call it from a terminal?

Code: Select all

sh yourscript.sh

Perhaps try bash yourscript.sh instead; running it with sh while you are using bash syntax is not funny

The only difference when bash is run as sh is the scripts it reads on invocation; all language features are still enabled.

Note that /bin/sh on Debian-based distros (such as Mint) is not bash; it is dash.

Try this:

Code: Select all

sudo ln /bin/bash /usr/local/bin/sh
PATH=/usr/local/bin:$PATH
sh -c 'q=qwert; echo "${q/w/W}"'


You will see that a bash feature not present in dash, in this case search and replace parameter expansion, is still available.