Strange problem with sed

[Masterofpsi]

I'm trying to write a sed script that will output the volume of my Master channel using amixer. This is the output from "amixer get Master":

Simple mixer control 'Master',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 64
  Mono: Playback 64 [100%] [0.00dB] [on]

So here is the script I have:

amixer get Master | grep % | sed 's/.*\([0-9]*\%\).*/\1/'

But my output is a mere percent sign --

%

It seems to me like the \1 should be a reference to zero or more numbers followed by a percent sign. Since regexes are greedy, shouldn't that tak up all of "100%"?

Can anyone help?

[tpl]

what about "grep Mono | cut f3 <filename"

[Masterofpsi]

Well, using cut, I might do:

amixer get Master | grep % | cut -c 21-25 | sed -e 's/\[//' -e 's/\]//'

But that's just awkward. And it still irks me that sed isn't behaving like it should.

[secondmouse]

try

amixer get Master | egrep -o "[0-9]+%"

if you don't have egrep, use

amixer get Master | grep -E -o "[0-9]+%"

[Masterofpsi]

That's even better than sed. Thanks.

[vonbiber]

I

amixer get Master | grep % | sed 's/.*\([0-9]*\%\).*/\1/'

But my output is a mere percent sign --

%

It seems to me like the \1 should be a reference to zero or more numbers followed by a percent sign. Since regexes are greedy, shouldn't that tak up all of "100%"?

To answer your question about sed.
This:
sed 's/.*\([0-9]*\%\).*/\1/'
removes all characters before '%'. You should have had this instead:

amixer get Master | grep % | sed 's/^[^\[]*\[\([0-9]*\%\).*/\1/'

which removes everything from the beginning of the line up to '['

[drl]

Hi.

As vonbiber noted, the initial ".*" is very greedy, matching everything up to the "%", and changes to the sed command can allow the match to succeed. In this case, a very short string could be added before the number string requirement. For example, adding the (escaped) "[" to the pattern:

#!/usr/bin/env bash

# @(#) s1	Demonstrate small change to sed command.

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) sed
set -o nounset
echo

FILE=${1-data1}

echo " Data file $FILE:"
cat $FILE

echo
echo " Results:"
grep % $FILE |
sed 's/.*\[\([0-9]*\%\).*/\1/'

exit 0

producing:

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0 
GNU bash 3.2.39
GNU sed version 4.1.5

 Data file data1:
Simple mixer control 'Master',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 64
  Mono: Playback 64 [100%] [0.00dB] [on]


 Results:
100%

cheers, drl