bash command redirecting output to file

freeindy · 11-07-2007, 02:16 PM

Hi,

I am trying to do something 'simple'

I have a bash program that gives output in the commad prompt eg.

Code:

00 12 03 C2 EE ...

I want to grep a line containing value 'C2' and put the line into a file.

I tried:

Code:

$./serial 1 | grep C2 > data

but it doesn't work. I don't get any errors but there is no data in the file. BTW, serial is the program that monitors serial port 1 and spits it out on the command.

Anyone knows how to do it?

Thanks a million.

Indy

pljvaldez · 11-07-2007, 03:09 PM

I think you might want the command tee.

Code:

$./serial 1 | grep C2 | tee data

WAJEDUR REHMAN · 11-07-2007, 03:46 PM

I'm not on a machine try this

$./serial 1 | cut -f4 > data

matthewg42 · 11-07-2007, 03:52 PM

Maybe this serial program is not printing to stdout, but instead stderr. When you do your command with grep, do you see the output of serial printed to the terminal in the same way that you would when you run without the grep?

If so, you should specify that the stderr should be sent to the stdout file handle:

Code:

$ ./serial 1 2>&1 | grep C2 > data

freeindy · 11-07-2007, 08:25 PM

thanks lads but none of them work. There is no data put into the file...

I wrote the serial program in C and it prints out with printf command, if that is in any help.

Indy

billymayday · 11-07-2007, 08:47 PM

ignore the file part for a moment. What do you get with

$./serial 1 | grep C2

matthewg42 · 11-08-2007, 03:05 AM

Using printf should print to standard output, unless you explicitly change the meaning of stdout in your program.

Then: what billymayday said.

freeindy · 11-08-2007, 04:36 AM

Billymayday:
I get exactly what I want. Everything is ignored except the line containing 'C2'. But when added the last part "> data", nothing is written to it.

mathewg42: Ok. Thanks.

Indy

billymayday · 11-08-2007, 04:40 AM

do you have write permission where you are running it?

try touch data and then .. >> data

freeindy · 11-08-2007, 05:18 AM

I beleive I have the permissions yes. I didn't understand your instuctions billymayday.

I tried "touch data". Nothing.
Then I also tried "./serial 1 | grep C2 >> data" and the file size is 0.

Indy

matthewg42 · 11-08-2007, 05:48 AM

>> appends to an existing file.
> truncates existing files.

Please can you enter these commands, and paste the results (with the commands too). pease everything.

Code:

echo $SHELL
id
ls -ld .
lsattr -d .
touch mytestfile
ls -l mytestfile
./serial 1 > mytestfile
cat mytestfile
./serial 1 |grep -i C2 > mytestfile
cat mytestfile

Please enclose your pasted results in [code] tags to aid readability. Don't omit anything. I'd like to see all output, and the commands as you typed them. If the un-filtered output of serial 1 is very long, please link to a nopaste posting for that output.