2-Cent Tips
2-cent Tip: Screenshots without X
Kapil Hari Paranjape [kapil at imsc.res.in]
Sat, 21 Mar 2009 07:50:04 +0530
Hello,
I had to do this to debug a program so I thought I'd share it.
X window dump without X
How does one take a screenshot without X? (For example, from the text console)
Use Xvfb (the X server that runs on a virtual frame buffer).
Steps:
1. Run Xvfb
$ Xvfb
This will usually start the X server :99
$ DISPLAY=:99 ; export DISPLAY
2. Run your application in the appropriate state.
$ firefox https://www.linuxgazette.net &
3. Find out which window id corresponds to your application
$ xwininfo -name 'firefox-bin' | grep id
Or
$ xlsclients
Use the hex string that you get as window id in the commands
below
4. Dump the screen shot of that window
$ xwd -id 'hexid" > firefox.xwd
5. If you want to, then kill these applications along with the
X server
$ killall Xvfb
'firefox.xwd' is the screenshot you wanted. Use 'convert' or on of the netpbm tools to convert the 'xwd' format to 'png' or whatever.
Additional Notes:
A. You can use a different screenshot program.
B. If you need to manipulate the window from the command line, then programmes like 'xautomation' and/or 'xwit' are your friends. Alternatively, use a WM like "fvwm" or "xmonad":
DISPLAY=:99 xmonad &This will allow you to manipulate windows from the command line if you know some Haskell!
Regards,
Kapil. --
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2-cent Tip: Lists of files by extension
Ben Okopnik [ben at linuxgazette.net]
Sat, 21 Mar 2009 15:36:49 -0400
Recently, I decided to sort, organize, and generally clean up my rather extensive music collection, and as a part of this, I decided to "flatten" the number of file types that were represented in it. Over the years, just about every type of audio file had made its way into it: FLAC, M4A, WMA, WAV, MID, APE, and so on, and so on. In fact, the first step would be to classify all these various types, get a list of each, and decide how to convert them to MP3s (see my next tip, which describes a generalized script to do just that.)
The process of collecting this kind of info wasn't unfamiliar to me; in fact, I'd previously done this, or something like it, with the "find" command when I was trying to establish what kind of files I'd want to index in a search database. This time, however, I took a bit of extra care to deal with names containing spaces, non-English characters, and files with no extensions. I also defined a list of files that I wanted to ignore (see the "User-modified vars" section of the script) and provided the option of specifying the directory to index (current one by default) and the directory in which to create the 'ext' files (/tmp/files<random_string>) by default; the script notifies you of the name.)
This isn't something that comes up often, but it can be very useful in certain situations.
#!/bin/bash
# Created by Ben Okopnik on Thu Mar 12 11:54:02 EDT 2009
# Creates a list of files named after all found extensions and containing the associated filenames
[ "$1" = "-h" -o "$1" = "--help" ] && { echo "${0##*/} [dir_to_read] [output_dir]"; exit 0; }
[ -n "$1" -a ! -d "$1" ] && { echo "'$1' is not a valid input directory"; exit 1; }
[ -n "$2" -a ! -d "$2" ] && { echo "'$2' is not a valid output directory"; exit 1; }
################ User-modified vars ########################
dir_root="/tmp/files"
ignore_exts="m3u bak"
################ User-modified vars ########################
snap=`pwd`
[ -n "$1" ] && snap="$1"
[ -n "$2" ] && dir_root="$2"
out_dir=`mktemp -d "${dir_root}XXX"`
echo "The output will be written to the '$out_dir' directory"
cd /
old=$IFS
IFS='
'
[ -n "`/bin/ls $out_dir`" ] && /bin/rm $out_dir/*
for n in `/usr/bin/find "$snap" -type f`
do
ext="`echo ${n/*.}|tr 'A-Z' 'a-z'`"
# Ignore all specified extensions
[ -n "`echo $ignore_exts|/bin/grep -i \"\\<$ext\\>\"`" ] && continue
# No extension means the substitution won't work; no substitution means
# we get the entire path and filename. So, no ext gets spun off to 'none'.
[ -n "`echo $ext|grep '/'`" ] && ext=none
echo $n >> $out_dir/$ext
done
echo "Done."
-- * Ben Okopnik * Editor-in-Chief, Linux Gazette * https://LinuxGazette.NET *
2-cent Tip: Converting from $FOO to MP3
Ben Okopnik [ben at linuxgazette.net]
Wed, 25 Mar 2009 10:03:21 -0400
Recently, while organizing my (very large) music library, I analyzed the whole thing and found out that I had almost 30 (!) different file types. Much of this was a variety of info files that came with the music (text, PDF, MS-docs, etc.) as well as image files in every conceivable format (which I ended up "flattening" to JPG) - but a large number of these were music formats of every kind, a sort of a living museum of "Music Formats Throughout the Ages." I decided to "flatten" all of that as well by converting all the odd formats to MP3.
Fortunately, there's a wonderful Linux app that will take pretty much every kind of audio - "mplayer" (https://www.mplayerhq.hu/DOCS/codecs-status.html#ac). It can also dump that audio to a single, easily-convertible format (WAV). As a result, I created a script that uses "mplayer" and "lame" to process a directory of music files called "2mp3".
It was surprisingly difficult to get everything to work together as it should, with some odd challenges along the way; for example, redirecting error output for either of the above programs was rather tricky. The script processes each file, creates an MP3, and appends to a log called '2mp3.LOG' in the current directory. It does not delete the original files - that part is up to you. Enjoy!
#!/bin/bash
# Created by Ben Okopnik on Mon Jul 2 01:16:32 EDT 2007
# Convert various audio files to MP3 format
#
# Copyright (C) 2007 Ben Okopnik <ben@okopnik.com>
# 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 2 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.
########## User-modifiable variables ###########################
set="*{ape,flac,m4a,wma,qt,ra,pcm,dv,aac,mlp,ac3,mpc,ogg}"
########## User-modifiable variables ###########################
# Need to have Bash expand the construct
set=`eval "ls -1 $set" 2>/dev/null`
# Set the IFS to a newline (i.e., ignore spaces and tabs in filenames)
IFS='
'
# Turn off the 'fake filenames' for failed matches
shopt -s nullglob
# Figure out if any of these files are present. 'ls' doesn't work (reports
# '.' for the match when no matching files are present) and neither does
# 'echo [pattern]|wc -w' (fails on filenames with spaces); this strange
# method seems to do just fine.
for f in "$set"; do ((count++)); done
[ -z "$count" ] && { echo "None of '$set' found; exiting."; exit 1; }
# Blow away the previous log, if any
[ ... ]
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