Finding duplicate files in the tree

find * -type f -exec md5sum \{\} \; | sort | uniq -D -W1 | less

Add quota support to new partition

quotacheck -gc -F vfsv0 /mount_point

Refresh framebuffer fonts

consolechars -f /usr/share/consolefonts/default8x16.psf.gz


echo $[ `ps aux | grep httpd | awk '{print $6}' | sed -e 's/$/+/'` 0 ]

Reverse cat, equivalent to GNU tac command

Use any of the following three:

sed -ne '1!G;h;$p' FILE
awk '{ lines[NR]=$0 }end {for(i=NR;i>0;i--) printlines }' FILE
perl -e 'print reverse <>' FILE

Reset the terminal

Keyboard press Ctrl-V Ctrl-O

Epoch to String

date -d'19700101 UTC 123456sec'

String to Epoch

date -d'2004-1-1 HKT 0:0:0' +%s

Killing blank lines and comments from a file

perl -pe '$_="" if (m/^\s*#/ || m/^$/)' FILE

UNIX newline to DOS newline

perl -pe 's/$/\r/' FILE

DOS newline to UNIX newline

perl -pe 's/\r//' FILE

Burning CD

mkisofs -JlqR -joliet-long -o file.iso $SOURCE_LIST
sudo cdrecord -dev=ATAPI:1,0,0 -driveropts=burnfree -gracetime=0 file.iso

Transcoding a MPEG movie from VCD to H.264+AAC

Tools used: mencoder (from mplayer, to extract and encode video into H.264 format), ffmpeg (to create AAC audio), mp4box (to multiplex video and audio)

mencoder $MPEG_FILE -ovc x264 -nosound -ni -sws 0 -x264encopts \
    threads=2:me=2:qp_constant=22:i4x4:keyint=120:nocabac:deblock:nob_adapt:bframes=1 \
    -ofps 25 -vop scale=320:240,pp=0x33,harddup -of rawvideo \
    -o $VIDEO_FILE
ffmpeg -i $VIDEO_FILE -i $MPEG_FILE -y -vn -f mp4 -acodec aac -ab 128 \
    -ar 48000 -ac 2 -map 1.1:0.0 $AAC_FILE
mp4box  -fps 25 -add $VIDEO_FILE -add $AAC_FILE -new $MP4_FILE

or in two-pass:

mencoder $MPEG_FILE -ovc x264 -nosound -ni -sws 0 -x264encopts \
    threads=2:me=2:bitrate=297:qp_min=22:qp_max=51:i4x4:keyint=120:cabac:deblock:nob_adapt:bframes=1:pass=1 \
    -passlogfile $LOG_FILE -ofps 25 -vop scale=352:288,pp=0x33,harddup -of rawvideo \
    -o $VIDEO_FILE
mencoder $MPEG_FILE -ovc x264 -nosound -ni -sws 0 -x264encopts \
    threads=2:me=2:bitrate=297:qp_min=22:qp_max=51:i4x4:keyint=120:cabac:deblock:nob_adapt:bframes=1:pass=2 \
    -passlogfile $LOG_FILE -ofps 25 -vop scale=352:288,pp=0x33,harddup -of rawvideo \
    -o $VIDEO_FILE
ffmpeg -i $VIDEO_FILE -i $MPEG_FILE -y -vn -f mp4 -acodec aac -ab 128 \
    -ar 44100 -ac 2 -map 1.1:0.0 $AAC_FILE
mp4box -fps 25 -add $VIDEO_FILE -add $AAC_FILE -new $MP4_FILE

This is the same thing from ffmpegX:

printf "Encoding started on " && date &&
ffmpeg -i $SOURCE_FILE -y \
    -itsoffset 0.5 -threads 1 -f psp -title 'Movie' \
    -vcodec h264 -b 296 -s 352x240 -r ntsc -g 250 -qmin 10 -qmax 51 \
    -acodec aac -ab 48 -ar 44100 -ac 2 -dct 8x8 -coder 1 \
printf "Encoding completed on " && date && printf "\a"
ffmpeg -i $SOURCE_FILE -an -f yuv4mpegpipe -s 640x480 -r 30000/1001 - |
x264 -v -A i4x4 -b 0 --qpmin 0 --qpmax 51 -B 791 \
    --me hex --threads 2 --level 51 --fps 30000/1001 \
    -o $VIDEO_FILE - 640x480 &&
ffmpeg -i $VIDEO_FILE -i $SOURCE_FILE -y -vn -f mp4 \
    -acodec aac -ab 128 -ar 48000 -ac 2 -map 1.1:0.0 $AUDIO_FILE &&
mp4box -fps 30000:1001 -add $VIDEO_FILE -add $AUDIO_FILE -new $OUTPUT_FILE

Transcoding using mencoder

mencoder \
    -vf scale -zoom -xy 640 -aspect 4:3 \  # Scale the video to 640x480
    -oac mp3lame \                         # Audio encode using MP3
    -ovc lavc \                            # Video encode using libavcodec
    -lavcopts vcodec=mpeg4:mbd=1:vbitrate=1500:threads=2 \
         # libavcodec options: MPEG4, bitrate, threads during encoding, etc.
    -o OUTPUT.AVI \                        # Output file
    INPUT1.mpg INPUT2.mpg ...              # Input files

Base64 Encoding and Decoding

perl -m'MIME::Base64' -pe '$_=MIME::Base64::decode($_);' base64.txt >
perl -m'MIME::Base64' -pe '$_=MIME::Base64::encode($_);' > base64.txt

Crop a range of lines from a text file

From line 1234 to line 1357 of a large text file, use any of these four:

head -1357 input.txt | tail $[ 1357-1234 ]
sed -n 1234,1357p input.txt
sed -n '1234,1357p;1358q' input.txt
awk 'NR>=1234&&NR<=1357' input.txt

sed option -n prohibits implicit output, the p command prints the lines, q command quit the stream upon a particular line. (Source: stackoverflow question)

“Open with” associations in GUI

Right click “open with” menu is populated from a combination of mimeinfo.cache and mimeapps.list files in the system. The file mimeinfo.cache is generated automatically from a bunch of defaults.list. The location of these files are (in precedence order):

  1. ~/.local/share/applications/mimeapps.list
  2. ~/.local/share/applications/defaults.list
  3. /usr/local/share/applications/defaults.list
  4. /usr/share/applications/defaults.list
  5. /usr/share/applications/mimeinfo.cache