the_naive the_naive - 10 days ago 4
C++ Question

How to parse pacmd list output and find sink indexes and names using QRegExp?

Normally from the terminal I use the command:

pacmd list-sinks|awk '/index:/ {print $0} /name:/ {print $0};'


which gives me an output like this:

index: 0
name: <alsa_output.pci-0000_01_00.1.hdmi-stereo>
index: 1
name: <alsa_output.pci-0000_00_1b.0.analog-stereo>
* index: 2
name: <alsa_output.usb-0d8c_C-Media_USB_Audio_Device-00-Device.iec958-stereo>


but apparently from
Qt
, when commanding using
QProcess
, parsing using
awk
isn't working, it just does not do any parsing at all and produces the whole output which you expect from commanding
pacmd list-sinks
. The whole output is as the following:

Welcome to PulseAudio! Use "help" for usage information.
>>> 3 sink(s) available.
index: 0
name: <alsa_output.pci-0000_01_00.1.hdmi-stereo>
driver: <module-alsa-card.c>
flags: HARDWARE DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
state: SUSPENDED
suspend cause: IDLE
priority: 9050
volume: 0: 45% 1: 45%
0: -20,78 dB 1: -20,78 dB
balance 0,00
base volume: 100%
0,00 dB
volume steps: 65537
muted: no
current latency: 0,00 ms
max request: 0 KiB
max rewind: 0 KiB
monitor source: 0
sample spec: s16le 2ch 44100Hz
channel map: front-left,front-right
Stereo
used by: 0
linked by: 0
configured latency: 0,00 ms; range is 0,50 .. 371,52 ms
card: 0 <alsa_card.pci-0000_01_00.1>
module: 5
properties:
alsa.resolution_bits = "16"
device.api = "alsa"
device.class = "sound"
alsa.class = "generic"
alsa.subclass = "generic-mix"
alsa.name = "HDMI 0"
alsa.id = "HDMI 0"
alsa.subdevice = "0"
alsa.subdevice_name = "subdevice #0"
alsa.device = "3"
alsa.card = "1"
alsa.card_name = "HDA NVidia"
alsa.long_card_name = "HDA NVidia at 0xf7080000 irq 17"
alsa.driver_name = "snd_hda_intel"
device.bus_path = "pci-0000:01:00.1"
sysfs.path = "/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1"
device.bus = "pci"
device.vendor.id = "10de"
device.vendor.name = "NVIDIA Corporation"
device.product.id = "0e1b"
device.product.name = "GK107 HDMI Audio Controller"
device.string = "hdmi:1"
device.buffering.buffer_size = "65536"
device.buffering.fragment_size = "32768"
device.access_mode = "mmap+timer"
device.profile.name = "hdmi-stereo"
device.profile.description = "Digital Stereo (HDMI)"
device.description = "GK107 HDMI Audio Controller Digital Stereo (HDMI)"
alsa.mixer_name = "Nvidia GPU 42 HDMI/DP"
alsa.components = "HDA:10de0042,104383f3,00100100"
module-udev-detect.discovered = "1"
device.icon_name = "audio-card-pci"
ports:
hdmi-output-0: HDMI / DisplayPort (priority 5900, latency offset 0 usec, available: no)
properties:
device.icon_name = "video-display"
active port: <hdmi-output-0>
index: 1
name: <alsa_output.pci-0000_00_1b.0.analog-stereo>
driver: <module-alsa-card.c>
flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
state: SUSPENDED
suspend cause: IDLE
priority: 9959
volume: 0: 27% 1: 27%
0: -34,20 dB 1: -34,20 dB
balance 0,00
base volume: 100%
0,00 dB
volume steps: 65537
muted: no
current latency: 0,00 ms
max request: 0 KiB
max rewind: 0 KiB
monitor source: 1
sample spec: s16le 2ch 48000Hz
channel map: front-left,front-right
Stereo
used by: 0
linked by: 0
configured latency: 0,00 ms; range is 0,50 .. 341,33 ms
card: 1 <alsa_card.pci-0000_00_1b.0>
module: 6
properties:
alsa.resolution_bits = "16"
device.api = "alsa"
device.class = "sound"
alsa.class = "generic"
alsa.subclass = "generic-mix"
alsa.name = "ALC269VB Analog"
alsa.id = "ALC269VB Analog"
alsa.subdevice = "0"
alsa.subdevice_name = "subdevice #0"
alsa.device = "0"
alsa.card = "0"
alsa.card_name = "HDA Intel PCH"
alsa.long_card_name = "HDA Intel PCH at 0xf7330000 irq 38"
alsa.driver_name = "snd_hda_intel"
device.bus_path = "pci-0000:00:1b.0"
sysfs.path = "/devices/pci0000:00/0000:00:1b.0/sound/card0"
device.bus = "pci"
device.vendor.id = "8086"
device.vendor.name = "Intel Corporation"
device.product.id = "1e20"
device.product.name = "7 Series/C210 Series Chipset Family High Definition Audio Controller"
device.form_factor = "internal"
device.string = "front:0"
device.buffering.buffer_size = "65536"
device.buffering.fragment_size = "32768"
device.access_mode = "mmap+timer"
device.profile.name = "analog-stereo"
device.profile.description = "Analog Stereo"
device.description = "Built-in Audio Analog Stereo"
alsa.mixer_name = "Realtek ALC269VB"
alsa.components = "HDA:10ec0269,1028052c,00100100"
module-udev-detect.discovered = "1"
device.icon_name = "audio-card-pci"
ports:
analog-output: Analog Output (priority 9900, latency offset 0 usec, available: unknown)
properties:

analog-output-speaker: Speakers (priority 10000, latency offset 0 usec, available: no)
properties:
device.icon_name = "audio-speakers"
analog-output-headphones: Headphones (priority 9000, latency offset 0 usec, available: yes)
properties:
device.icon_name = "audio-headphones"
active port: <analog-output-headphones>
* index: 2
name: <alsa_output.usb-0d8c_C-Media_USB_Audio_Device-00-Device.iec958-stereo>
driver: <module-alsa-card.c>
flags: HARDWARE DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
state: RUNNING
suspend cause:
priority: 9048
volume: 0: 45% 1: 45%
0: -20,78 dB 1: -20,78 dB
balance 0,00
base volume: 100%
0,00 dB
volume steps: 65537
muted: no
current latency: 31,29 ms
max request: 4 KiB
max rewind: 344 KiB
monitor source: 4
sample spec: s16le 2ch 48000Hz
channel map: front-left,front-right
Stereo
used by: 1
linked by: 1
configured latency: 26,00 ms; range is 26,00 .. 1837,50 ms
card: 3 <alsa_card.usb-0d8c_C-Media_USB_Audio_Device-00-Device>
module: 22
properties:
alsa.resolution_bits = "16"
device.api = "alsa"
device.class = "sound"
alsa.class = "generic"
alsa.subclass = "generic-mix"
alsa.name = "USB Audio"
alsa.id = "USB Audio"
alsa.subdevice = "0"
alsa.subdevice_name = "subdevice #0"
alsa.device = "0"
alsa.card = "2"
alsa.card_name = "C-Media USB Audio Device"
alsa.long_card_name = "C-Media USB Audio Device at usb-0000:00:14.0-1, full speed"
alsa.driver_name = "snd_usb_audio"
device.bus_path = "pci-0000:00:14.0-usb-0:1:1.0"
sysfs.path = "/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0/sound/card2"
udev.id = "usb-0d8c_C-Media_USB_Audio_Device-00-Device"
device.bus = "usb"
device.vendor.id = "0d8c"
device.vendor.name = "C-Media Electronics, Inc."
device.product.id = "000c"
device.product.name = "Audio Adapter"
device.serial = "0d8c_C-Media_USB_Audio_Device"
device.string = "iec958:2"
device.buffering.buffer_size = "352800"
device.buffering.fragment_size = "176400"
device.access_mode = "mmap+timer"
device.profile.name = "iec958-stereo"
device.profile.description = "Digital Stereo (IEC958)"
device.description = "Audio Adapter Digital Stereo (IEC958)"
alsa.mixer_name = "USB Mixer"
alsa.components = "USB0d8c:000c"
module-udev-detect.discovered = "1"
device.icon_name = "audio-card-usb"
ports:
iec958-stereo-output: Digital Output (S/PDIF) (priority 0, latency offset 0 usec, available: unknown)
properties:

active port: <iec958-stereo-output>
>>>


I guess I'm commanding the wrong way. The code I use for commanding and parsing using
awk
is the following:

QString prog = "pacmd";
QStringList arguments;
QProcess p;
arguments << "list-sinks"<<"|awk '/index:/ {print $0} /name:/ {print $0};'";
QString reply;
p.start(prog, arguments);
if (p.waitForStarted())
{
p.waitForFinished();
reply = p.readAllStandardOutput();
qDebug()<<reply<<endl;
}
else
{
qDebug()<< "Error using pacmd for getting list of sinks";
}


So, now, I'm trying to parse the indexes and the names without using
awk
. I'm able to find the indexes, but not the names. The code is as the following:

QString prog = "pacmd";
QStringList arguments;
QProcess p;
arguments << "list-sinks";
QString reply;
p.start(prog, arguments);
if (p.waitForStarted())
{
p.waitForFinished();
reply = p.readAllStandardOutput();
QRegExp rx("index: \\d+|'", Qt::CaseInsensitive);
QStringList indexList;
int pos = 0;
while ((pos = rx.indexIn(reply, pos)) != -1) {
indexList << rx.capturedTexts();
pos += rx.matchedLength();
}
foreach (QString index, indexList) {
qDebug()<<index;
}

QRegExp rx1("name: \\s*|'", Qt::CaseInsensitive);
QStringList nameList;
pos = 0;
while ((pos = rx1.indexIn(reply, pos)) != -1) {
nameList << rx1.capturedTexts();
pos += rx1.matchedLength();
}
foreach (QString index, nameList) {
qDebug()<<index;
}
}
else
{
qDebug()<< "Error using pacmd for getting list of sinks";
}


The output I get from the code is the following:

"index: 0"
"index: 1"
"index: 2"
"name: "
"name: "
"name: "


How can I get the names as well like the following string?

name: <alsa_output.pci-0000_01_00.1.hdmi-stereo>


Is
"name: \\s*|'"
not the correct pattern for regexp for capturing the name as well?

Thanks.

Answer

First off the reason why your first try running awk didn't work:

The pipe '|' is a feature of the shell (e.g. bash). When you run an executable with QProcess, this doesn't run the executable in a shell, it runs the executable directly. In your code, the pacmd executable is therefore run with the command line arguments list-sinks and |awk '/index:/ {print $0} /name:/ {print $0};'.

To make it work you either need to first run list-sinks, get its output, and then run awk and pass it this as the input, or if you are fine with depending on a specific shell, you can also run the shell and pass your command line to it (in the case of bash you'd pass -c and pacmd list-sinks|awk '/index:/ {print $0} /name:/ {print $0};' as arguments to /bin/bash).

Regarding parsing for name: something with regular expressions, the expression \s matches whitespace. So just change name: \\s* to name: \\S* (with an upper case S) for getting non-whitespace characters.