C2110 UNIX and programming 10th lesson -1C2110
UNIX and programming
Petr Kulhánek, Jakub Štěpán
kulhanek@chemi.muni.cz
National Centre for Biomolecular Research, Faculty of Science
Masaryk University, Kotlářská 2, CZ-61137 Brno
CZ.1.07/2.2.00/15.0233
10. lekce
C2110 UNIX and programming 10th lesson -2-
Contents
 Running commands III
• Variable PATH
 Hybrid scripts
• Redirection in scripts
 Commands
• type, hash, tr, memcoder, mplayer
C2110 UNIX and programming 10th lesson -3Running
commands III
 Variable PATH
 Commands
• tr, mplayer, mencoder
C2110 UNIX and programming 10th lesson -4Running
commands and apps, III
1. Path to command is first looked up in recently used commands table:
$ hash
hits command
1 /bin/rm
3 /bin/ls
2. If no path is found, then directories given in variable PATH are searched.
$ echo $PATH
.../usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
3. To find out that path exists use command type
$ type ls
/bin/ls
Search order
Table may be erased by command:
$ hash -r
Directories should be separated by : (colon)
For shell to be able to run any command, it needs to have full path to file, which contains
binary code of program or script.
C2110 UNIX and programming 10th lesson -5Adjusting
variable PATH
Manual change of value of variable PATH
$ export PATH=/my/path/to/my/commands:$PATH
separator
Path to directory with, that are to be
accessible without need to write full path.
Path has to be in absolute form! (relative
path is security risk).
Previous value of PATH variable (necessary for
system commands to be found)
Automatic PATH value adjustment
Automatic change of variable PATH value (and possibly other system variables) may be
done by command module.
$ module add vmd
C2110 UNIX and programming 10th lesson -6Commands
for exercise
Command tr is may be used to transform or delete symbols from standard input. Result is
printed to standard output.
Examples:
$ cat soubor.txt | tr --delete "qwe"
$ cat soubor.txt | tr --delete "[:space:]"
$ echo $PATH | tr ":" "\n"
From soubor.txt contents symbols "q", "w" and "e" are removed.
From soubor.txt file contents all white spaces are removed.
All symbols ":" echoed to standard input of tr will be
replaced by new line symbol "\n"
C2110 UNIX and programming 10th lesson -7-
Exercise
1. Print variable PATH contents.
2. Print directories from variable PATH, each to separate line.
3. What directory contains program kwrite?
4. Print contents of recently used commands table.
5. Find out how command module add vmd change variable PATH.
6. Find directory where is command vmd?
C2110 UNIX and programming 10th lesson -8-
MPlayer
MPlayer is useful command to play video. Short usage description is provided by
submitting command with no argument.
Example:
$ mplayer movie.avi
play video movie.avi
Interesting options:
-loop N play N loops
-fs play video in full screen mode
http://www.mplayerhq.hu
C2110 UNIX and programming 10th lesson -9-
MEncoder
MEncoder is command to code video. It may be used to convert video formats, codec
change or creating video from picture frames.
Creating video from picture frames:
$ mencoder "mf://*.png" –mf fps=25 -ovc lavc -o output.avi
Input data. Use all files with extension
png. Pictures sequence is sorted
according to file names.
Output encoder. Output file name.
Overview: http://mariovalle.name/mencoder/mencoder.html
Frame rate per second (FPS – frames
per second).
C2110 UNIX and programming 10th lesson -10-
Alternatives
FFmpeg is a complete, cross-platform solution to record, convert and stream audio
and video. It includes libavcodec - the leading audio/video codec library.
GStreamer is a library for constructing graphs of media-handling components. The
applications it supports range from simple Ogg/Vorbis playback, audio/video
streaming to complex audio (mixing) and video (non-linear editing) processing.
http://gstreamer.freedesktop.org/
http://ffmpeg.org/
C2110 UNIX and programming 10th lesson -11-
Exercise
1. Copy two files with avi extension from directory /home/kulhanek/Data/Video to
subdirectory of your home my_video, which will be in your home directory.
2. Play both video files in program mplayer. Learn basic program functions: pause
video, rewind video, switch to full screen.
3. Directory /home/kulhanek/Data/MovieImages contains pictures in png format.
Create directory /scratch/your_login/images , copy images to that directory.
4. Find size (width, height and bit depth) does have image e_0010.png?
5. Create two videos with FPS=10 and FPS=50 from images.
6. Play created videos.
C2110 UNIX and programming 10th lesson -12Hybrid
scripts
 Redirection in scripts
C2110 UNIX and programming 10th lesson -13Redirection
in script
Redirection of standard input of program my_command from script file.
.......
./my_command << EOF
First text line
Second text line
Third text line
EOF
......
Input end mark (user choice)
End of input, mark must not be
surrounded by spaces
text (input data)
This redirection form is especially advantageous in scripts, it works in command line as well.
Advantage is variables expansion in input text.
C2110 UNIX and programming 10th lesson -14-
Showcase
#!/bin/bash
gnuplot << EOF
plot sin(x)
EOF
#!/bin/bash
for((I=1;$I<=10;I++)); do
NAME=`printf "%02d.txt" $I`
cat << EOF > $NAME
This is file number: $I
EOF
done
Highlighted text is sent to standard input
of cat command, variables are expanded
in advance, resulting text is saved to file
$NAME.
In this way gnuplot scripts may be automatically
generated.
Result of command in backward
apostrophes `` is saved to variable NAME.
C2110 UNIX and programming 10th lesson -15-
Exercise
1. Write script, that creates ten files. Each file with name in format XX.txt,
where XX is file number. For numbers les then 10 use leading zero to keep
file name length. Each file will contain following text (X is file number):
2. Write script(s), that creates set of images showing moving waves (function
sin, or cos in 2D or 3D, up to your choice). Create video from files using
command mencoder. Play video by command mplayer.
Automaticaly created text file
File number is: X