Linux retrieve monitor names - linux

Question

Situation: I'm using multiple monitors and I want to get their names in bash. Currently I'm using Ubuntu 10.04.
I know about xrandr. From it I can get only statistics data. What I want is to read all monitor names in an array to work with them.
Is there a clear way to do that without cutting names from some kind of string? A clear way would be reading them from file. A not clear way would be to pipe xrandr output to some sort a function to cut names out from it.

Answer 1

Inspired by Beni's answer, this will read the EDID data using xrandr and extract the monitors names according to the EDID specification, with no need of any external tools like parse-edid:
#!/bin/bash
while read -r output hex conn; do
[[ -z "$conn" ]] && conn=${output%%-*}
echo "# $output $conn $(xxd -r -p <<< "$hex")"
done < <(xrandr --prop | awk '
!/^[ \t]/ {
if (output && hex) print output, hex, conn
output=$1
hex=""
}
/ConnectorType:/ {conn=$2}
/[:.]/ && h {
sub(/.*000000fc00/, "", hex)
hex = substr(hex, 0, 26) "0a"
sub(/0a.*/, "", hex)
h=0
}
h {sub(/[ \t]+/, ""); hex = hex $0}
/EDID.*:/ {h=1}
END {if (output && hex) print output, hex, conn}
' | sort
)
Uses awk to precisely extract the monitor name only, and no extra garbage from the EDID, hence "magic numbers" like 000000fc00, 26 and 0a. Finally uses xxd to convert from hex to ASCII, printing one monitor name per line.
Based on this solution I made a handy script to switch monitors, which can also be used to simply list monitor info:
$ monitor-switch --list
Connected monitors:
# DFP5 HDMI HT-R391
# DFP7 DVI-I DELL U2412M
$ monitor-switch --list
Connected monitors:
# DisplayPort-1 DisplayPort DELL U2412M
# DisplayPort-3 DisplayPort DELL U2415
# HDMI-A-2 HDMI LG TV

Answer 2

Tested on Ubuntu 16.04, 18.04. (I know its too late to answer but this solution is relevant today)
$ sudo apt-get install -y hwinfo
...
$ hwinfo --monitor --short
monitor:
SONY TV
AUO LCD Monitor
I have two monitors attached. One with the laptop and the other is an external display. As soon as the external monitor is plugged-in or out, this command reflects the change. You continuously need to poll. Removing the --short option gives more detailed information.
You can poll the state with the following background job:
$ while true;
> do
> hwinfo --monitor --short;
> sleep 2;
> done >> monitor.log &
The while true loop runs infinite times. The sleep 2 pauses each iteration of the loop for 2 seconds. And the output of hwinfo --monitor --short is appended to monitor.log. This log file can give you the activity history of monitor plug-in and plug-out.
FYI: I am using a background (daemon) python script using the above command (and other similar ones) to detect if someone is doing some HW plug-ins and plug-outs with the systems in the computer lab. If so, I get appropriate notifications that someone plugged-out/in a monitor, mouse or keyboard in almost real-time!
More info about hwinfo command is here. Its man page is also a good source.

Answer 3

sudo get-edid didn't work for me. (EDIT: now works on another computer, Lubuntu 14.10; I'd blame BIOS differences but that's a random guess...)
Anyway under X, xrandr --verbose prints the EDID block. Here is a quick and dirty way to extract it and pass to parse-edid:
#!/bin/bash
xrandr --verbose | perl -ne '
if ((/EDID(_DATA)?:/.../:/) && !/:/) {
s/^\s+//;
chomp;
$hex .= $_;
} elsif ($hex) {
# Use "|strings" if you dont have read-edid package installed
# and just want to see (or grep) the human-readable parts.
open FH, "|parse-edid";
print FH pack("H*", $hex);
$hex = "";
}'

Answer 4

If you don't want to parse xrandr output, write a C program using libXrandr that gets only what you want. If all you want to do is to query information, it can be done quickly. Read this document.
If you want to get the real monitor name, an alternative to #dtmilano's solution is to get the EDID property of the monitor using libXrandr and then manually parse it and print (read the EDID specification).
xrandr source code.

Answer 5

I know this is a dirty way, but it gives me some monitor model name even better than sudo get-edid|parse-edid. It reads information in arrays, and outputs it in a way that can be read like you would read a file. You may modify it according to your needs.
#!/bin/bash
#
#
# get-monitors.sh
#
# Get monitor name and some other properties of connected monitors
# by investigating the output of xrandr command and EDID data
# provided by it.
#
# Copyright (C) 2015,2016 Jarno Suni <8#iki.fi>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. See <http://www.gnu.org/licenses/gpl.html>
set -o nounset
set -o errexit
# EDID format:
# http://en.wikipedia.org/wiki/Extended_Display_Identification_Data#EDID_1.3_data_format
# http://read.pudn.com/downloads110/ebook/456020/E-EDID%20Standard.pdf
declare -r us=';' # separator string;
# If EDID has more than one field with same tag, concatenate them,
# but add this string in between.
declare -r fs=$'\x1f' # Field separator for internal use;
# must be a character that does not occur in data fields.
declare -r invalid_edid_tag='--bad EDID--'
# If base EDID is invalid, don't try to extract information from it,
# but assign this string to the fields.
# Get information in these arrays:
declare -a outs # Output names
declare -a conns # Connection type names (if available)
declare -a names # Monitor names (but empty for some laptop displays)
declare -a datas # Extra data; may include laptop display brand name
# and model name
declare -i no # number of connected outputs (to be counted)
# xrandr command to use as a source of information:
declare -r xrandr_output_cmd="xrandr --prop"
hex_to_ascii() {
echo -n "$1" | xxd -r -p
}
ascii_to_hex() {
echo -n "$1" | xxd -p
}
get_info() {
no=0
declare OIFS=$IFS;
IFS=$fs
while read -r output conn hexn hexd; do
outs[no]="${output}"
conns[no]="${conn}"
names[no]="$(hex_to_ascii "$hexn")"
datas[no]="$(hex_to_ascii "$hexd")"
(( ++no ))
done < <(eval $xrandr_output_cmd | gawk -v gfs="$fs" '
function print_fields() {
print output, conn, hexn, hexd
conn=""; hexn=""; hexd=""
}
function append_hex_field(src_hex,position,app_hex, n) {
n=substr(src_hex,position+10,26)
sub(/0a.*/, "", n)
# EDID specification says field ends by 0x0a
# (\n), if it is shorter than 13 bytes.
#sub(/(20)+$/, "", n)
# strip whitespace at the end of ascii string
if (n && app_hex) return app_hex sp n
else return app_hex n
}
function get_hex_edid( hex) {
getline
while (/^[ \t]*[[:xdigit:]]+$/) {
sub(/[ \t]*/, "")
hex = hex $0
getline
}
return hex
}
function valid_edid(hex, a, sum) {
if (length(hex)<256) return 0
for ( a=1; a<=256; a+=2 ) {
# this requires gawk
sum+=strtonum("0x" substr(hex,a,2))
# this requires --non-decimal-data for gawk:
#sum+=sprintf("%d", "0x" substr(hex,a,2))
}
if (sum % 256) return 0
return 1
}
BEGIN {
OFS=gfs
}
/[^[:blank:]]+ connected/ {
if (unprinted) print_fields()
unprinted=1
output=$1
}
/[^[:blank:]]+ disconnected/ {
if (unprinted) print_fields()
unprinted=0
}
/^[[:blank:]]*EDID.*:/ {
hex=get_hex_edid()
if (valid_edid(hex)) {
for ( c=109; c<=217; c+=36 ) {
switch (substr(hex,c,10)) {
case "000000fc00" :
hexn=append_hex_field(hex,c,hexn)
break
case "000000fe00" :
hexd=append_hex_field(hex,c,hexd)
break
}
}
} else {
# set special value to denote invalid EDID
hexn=iet; hexd=iet
}
}
/ConnectorType:/ {
conn=$2
}
END {
if (unprinted) print_fields()
}' sp=$(ascii_to_hex $us) iet=$(ascii_to_hex $invalid_edid_tag))
IFS="$OIFS"
}
get_info
# print the colums of each display quoted in one row
for (( i=0; i<$no; i++ )); do
echo "'${outs[i]}' '${conns[i]}' '${names[i]}' '${datas[i]}'"
done

Answer 6

You may try ddcprobe and/or get-edid
$ sudo apt-get install xresprobe read-edid
$ sudo ddcprobe
$ sudo get-edid

Answer 7

You're looking for EDID information, which is passed along an I²C bus and interpreted by your video driver. As dtmilano says, get-edit from ddcprobe should work.
You can also get this information by logging your X start:
startx -- -logverbose 6
Years ago, I used a package called read-edid to gather this information.
The read-edid package may be available in Ubuntu already, according to this blog post from 2009.