Shell scripting peculiarity

Dogs · 01-22-2010, 06:52 PM

In this example, why does blacklist end up in the file blacklist and $a end up in stdout?

Code:

#!/bin/sh
test= 'lsmod' | 'awk' '/snd_/{print $1}' > audiodrivers

while a=read line
do 
   echo -n "blacklist $a" >> test.txt
done < /root/testscript/audiodrivers

The desired result is to have a file containing the results of lsmod which had the first word on the line beginning with snd_ copied into another file preceded by the word blacklist

so audiodrivers contains
snd_driver1
snd_driver2
etc

and blacklist will contain
blacklist snd_driver1
blacklist snd_driver2
etc

ta0kira · 01-22-2010, 07:02 PM

Quote:

Originally Posted by Dogs

In this example, why does blacklist end up in the file blacklist and $a end up in stdout?

Code:

#!/bin/sh
test= 'lsmod' | 'awk' '/snd_/{print $1}' > audiodrivers

while a=read line
do 
   echo -n "blacklist $a" >> test.txt
done < /root/testscript/audiodrivers

Maybe you need this?

Code:

lsmod | grep 'snd_' | while read a; do
  echo "blacklist $a" >> test.txt
done

Kevin Barry

Dogs · 01-22-2010, 07:28 PM

Code:

#!/bin/bash
lsmod | awk '/snd_/{print $1}' | while read a; do
  echo "blacklist $a" >> test.txt
done

That's much better. Thank you =)

I'd still like to know why in the original code the echo command would be split in half..

As if I'd typed

Code:

while a=read line
do 
   echo -n "blacklist " >> test.txt
   echo "$a"         #goes to stdout, with newline

done < /root/testscript/audiodrivers

instead of

Code:

while a=read line
do 
   echo -n "blacklist $a" >> test.txt
done < /root/testscript/audiodrivers

ta0kira · 01-22-2010, 07:35 PM

I'm not even sure what the syntactic meaning of while a=read line is. I'm surprised it does anything at all. Likewise with the test= line.
Kevin Barry

ghostdog74 · 01-22-2010, 07:51 PM

Quote:

Originally Posted by Dogs

Code:

#!/bin/sh
test= 'lsmod' | 'awk' '/snd_/{print $1}' > audiodrivers

while a=read line
do 
   echo -n "blacklist $a" >> test.txt
done < /root/testscript/audiodrivers

all the above is redundant

Code:

lsmod | awk '/snd_/{print "blacklist "$1 > "test.txt"}'