http://code.google.com/p/osd-lyrics/
I used to have lrcshow-x, but it seems to be hard to install and do not cache lyrics locally. From the osdlyrics download file list, use the 0.4.0 version for Ubuntu 10.04 (Lucid). Newer versions are broken in MPRIS2 protocol handling, see here.
This post covers the loop usage of bash shell. NOTE: read inline comments carefully 🙂
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 |
#!/bin/bash # loop list, last value remains for test in Alabama Alaska Arizona Arkansas California Colorado do echo The next state is $test done echo "The last state we visited was $test" test=Connecticut echo "Wait, now we're visiting $test" # using escape or quote for test in I don\'t know if "this'll" work do echo "word: $test" done # loop variable & files states="Alabama Alaska Arizona Arkansas Colorado Connecticut Delaware Florida Georgia" statesfile=states.txt for state in $states; do echo $state >> $statesfile done for state in `cat $statesfile`; do echo "Visit beautiful $state" done rm $statesfile # loop directory for file in ~/.b*; do if [ -d "$file" ]; then echo "$file is a directory" elif [ -f "$file" ]; then echo "$file is a file" else echo "$file doesn't exist" fi done # c-style syntax for (( i = 1; i <= 10; i++ )); do echo "The next number is $i" done # IFS (internal field separator) to separator string IFSHOLD=$IFS IFS=$'\n' for entry in `cat /etc/passwd`; do echo "Values in $entry:" IFS=: for value in $entry; do echo " $value" done done IFS=$IFSHOLD |
|
1 2 3 4 5 6 7 |
#!/bin/bash var1=10 while [ $var1 -gt 0 ]; do echo $var1 var1=$[ $var1 - 1 ] done |
|
1 2 3 4 5 6 7 |
#!/bin/bash var1=100 until [ $var1 -eq 0 ]; do echo $var1 var1=$[ $var1 - 25 ] done |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 |
#!/bin/bash # break for (( a = 1; a < 4; a++ )); do echo "Outer loop: $a" for (( b = 1; b < 100; b++ )); do if [ $b -eq 5 ]; then break fi echo "Inner loop: $b" done done # break outer loop for (( a = 1; a < 4; a++ )); do echo "Outer loop: $a" for (( b = 1; b < 100; b++ )); do if [ $b -eq 5 ]; then break 2 fi echo "Inner loop: $b" done done # continue outer loop for (( a = 1; a <= 5; a++ )); do echo "Iteration $a:" for (( b = 1; b < 3; b++ )); do if [ $a -gt 2 ] && [ $a -lt 4 ]; then continue 2 fi var3=$[ $a * $b ] echo " The result of $a * $b is $var3" done done |
There may be times when you’re in an inner loop but need to stop the outer loop. The break command includes a single command line parameter value: break n where n indicates the level of the loop to break out of. By default, n is 1, indicating to break out of the current loop. If you set n to a value of 2, the break command will stop the next level of the outer loop.
Finally, you can either pipe or redirect the output of a loop within your shell script.
|
1 2 3 4 5 6 7 8 9 |
#!/bin/bash testfile=testloop.txt for (( a = 1; a < 10; a++ )); do echo "The number is $a" done > $testfile echo "The command is finished." cat $testfile rm $testfile |
When creating a shell script file, you must specify the shell you are using in the first line of the file. The format for this is:
|
1 2 3 4 |
#!/bin/bash # This script displays the date and who's logged on date who |
In a normal shell script line, the pound sign(#) is used as a comment line. A comment line in a shell script isn’t processed by the shell. However, the first line of a shell script file is a special case, and the pound sign followed by the exclamation point tells the hell what shell to run the script under (yes, you can be using a bash shell and run your script using another shell).
The echo command can display a simple text string if you add the string following the command.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
#!/bin/bash # basic usage echo This is a test. echo "Let's see if this'll work" # environment variables echo "User info for user: $USER" echo UID: $UID echo HOME: $HOME echo "The cost of the item is \$15" # user variables days=10 guest="Katie" echo "$guest checked in $days days ago" days=5 guest="Jessica" echo "$guest checked in $days days ago" # backtip testing=`date` echo "The date and time are: " $testing |
The echo command uses either double or single quotes to delineate text strings. If you use them within your string, you need to use one type of quote within the text and the other type to delineate the string.
Notice that the environment variables in the echo commands are replaced by their current values when the script is run. Also notice that we were able to place the $USER system variable within the double quotation marks in the first string, and the shell script was still able to figure out what we meant.
You may also see variables referenced using the format ${variable}. The extra braces around the variable name are often used to help identify the variable name from the dollar sign.
User variables can be any text string of up to 20 letters, digits, or an underscore character. User variables are case sensitive, so the variable Var1 is different from the variable var1. This little rule often gets novice script programmers in trouble.
Values are assigned to user variables using an equal sign. No spaces can appear between the variable, the equal sign, and the value (another trouble spot for novices). Here are a few examples of assigning values to user variables.
The shell script automatically determines the data type used for the variable value. Variables defined within the shell script maintain their values throughout the life of the shell script but are deleted when the shell script completes.
Just like system variables, user variables can be referenced using the dollar sign. It’s important to remember that when referencing a variable value you use the dollar sign, but when referencing the variable to assign a value to it, you do not use the dollar sign.
The backtick allows you to assign the output of a shell command to a variable.
>: output redirect
>>: output redirect append data
<: input redirect
<<: inline input redirect
|
1 2 3 4 5 6 7 |
# wc << EOF > test string 1 > test string 2 > test string 3 > EOF 3 9 42 # |
The inline input redirection symbol is the double less-than symbol (<<). Besides this symbol, you must specify a text marker that delineates the beginning and end of the data used for input. You can use any string value for the text marker, but it must be the same at the beginning of the data and the end of the data.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
#!/bin/bash var1=10 var2=3 var3=`expr $var1 \* $var2` var4=$[$var1 * $var2] var5=`expr $var1 / $var2` var6=$[$var1 / $var2] var7=`echo "scale=3; $var1 / $var2" | bc` echo The result is $var3 echo The result is $var4 echo The result is $var5 echo The result is $var6 echo The result is $var7 |
The expr command allowed the processing of equations from the command line. Note the spaces around operator is necessary. Escape character(backslash) is used to identify any characters that may be misinterpreted by the shell before being passed to the expr command.
Bash also provides a much easier way of performing mathematical equations. In bash, when assigning a mathematical value to a variable, you can enclose the mathematical equation using a dollar sign and square brackets ($[ operation ]).
The bash shell mathematical operators support only integer arithmetic. The most popular solution uses the built-in bash calculator, called bc.
The bash shell if statement runs the command defined on the if line. If the exit status of the command is zero (the command completed successfully), the commands listed under the then section are executed. If the exit status of the command is anything else, the then commands aren’t executed, and the bash shell moves on to the next command in the script.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 |
#!/bin/bash user=gonwan user2=test2 user3=test3 # if-then if grep $user /etc/passwd; then echo "The bash files for user $user are:" ls -a /home/$user/.b* fi # if-then-else if grep $user2 /etc/passwd; then echo "The bash files for user $user2 are:" ls -a /home/$user2/.b* else echo "The user name $user2 does not exist on this system" fi #if-then-elif-then-else if grep $user3 /etc/passwd; then echo "The bash files for user $user3 are:" ls -a /home/$user3/.b* elif grep $user2 /etc/passwd; then echo "The bash files for user $user2 are:" ls -a /home/$user2/.b* else echo "The user name $user2 and $user3 does not exist on this system" fi |
The test command provides a way to test different conditions in an if-then statement. If the condition listed in the test command evaluates to true, the test command exits with a zero exit status code, making the if-then statement behave in much the same way that if-then statements work in other programming languages. If the condition is false, the test command exits with a 1, which causes the if-then statement to fail.
| Comparison | Description |
| n1 -eq n2 | Check if n1 is equal to n2. |
| n1 -ge n2 | Check if n1 is greater than or equal to n2. |
| n1 -gt n2 | Check if n1 is greater than n2. |
| n1 -le n2 | Check if n1 is less than or equal to n2. |
| n1 -lt n2 | Check if n1 is less than n2. |
| n1 -ne n2 | Check if n1 is not equal to n2. |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
#!/bin/bash val1=10 val2=11 if [ $val1 -gt $val2 ]; then echo "$val1 is greater than $val2" else echo "$val1 is less than $val2" fi if (( $val1 > $val2 )); then echo "$val1 is greater than $val2" else echo "$val1 is less than $val2" fi |
However, The test command wasn’t able to handle the floating-point value.
You may also notice usage of double parentheses. It provide advanced mathematical formulas for comparisons, no escape is needed in it:
| Symbol | Description |
| val++ | Post-increment |
| val– | Post-decrement |
| ++val | Pre-increment |
| –val | Pre-decrement |
| ! | Logical negation |
| ∼ | Bitwise negation |
| ** | Exponentiation |
| << | Left bitwise shift |
| >> | Right bitwise shift |
| & | Bitwise Boolean AND |
| | | Bitwise Boolean OR |
| ** | Exponentiation |
| && | && Logical AND |
| || | Logical OR |
| Comparison | Description |
| str1 = str2 | Check if str1 is the same as string str2. |
| str1 != str2 | Check if str1 is not the same as str2. |
| str1 < str2 | Check if str1 is less than str2. |
| str1 > str2 | Check if str1 is greater than str2. |
| -n str1 | Check if str1 has a length greater than zero. |
| -z str1 | Check if str1 has a length of zero. |
Trying to determine if one string is less than or greater than another is where things start getting tricky. There are two problems that often plague shell programmers when trying to use the greater-than or less-than features of the test command:
– The greater-than and less-than symbols must be escaped, or the shell will use them as redirection symbols, with the string values as filenames.
– The greater-than and less-than order is not the same as that used with the sort command.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
#!/bin/bash val1=ben val2=mike if [ $val1 \> $val2 ]; then echo "$val1 is greater than $val2" else echo "$val1 is less than $val2" fi if [[ $val1 > $val2 ]]; then echo "$val1 is greater than $val2" else echo "$val1 is less than $val2" fi |
The double bracketed expression uses the standard string comparison used in the test command. However, it provides an additional feature that the test command doesn’t, pattern matching. No escape is needed anymore.
Capitalized letters are treated as less than lowercase letters in the test command. However, when you put the same strings in a file and use the sort command, the lowercase letters appear first. This is due to the ordering technique each command uses. The test command uses standard ASCII ordering, using each character’s ASCII numeric value to determine the sort order. The sort command uses the sorting order defined for the system locale language settings. For the English language, the locale settings specify that lowercase letters appear before uppercase letters in sorted order.
While the BashFAQ said: As of bash 4.1, string comparisons using < or > respect the current locale when done in [[, but not in [ or test. In fact, [ and test have never used locale collating order even though past man pages said they did. Bash versions prior to 4.1 do not use locale collating order for [[ either. So you get opposite result when running on CentOS-5.7(bash-3.2) and Ubuntu-10.04(bash-4.1) with [[ operator. And bash-4.1 is consistent with sort command now.
Well, this is easy, just walk through the snippet:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
#!/bin/bash case $USER in gonwan | barbara) echo "Welcome, $USER" echo "Please enjoy your visit" ;; testing) echo "Special testing account" ;; jessica) echo "Do not forget to log off when you're done" ;; *) echo "Sorry, you are not allowed here" ;; esac |
All sample code are tested under CentOS-5.7 and Ubuntu-10.04.
In this first post of the series, some basic concepts are introduced. All information from Linux Command Line and Shell Scripting Bible, Second Edition.
There are three ways of starting a bash shell:
– As a default login shell at login time
– As an interactive shell that is not the login shell
– As a non-interactive shell to run a script
When you log in to the Linux system, the bash shell starts as a login shell. The login shell looks for four different startup files to process commands from. The following is the order in which the bash shell processes the files:
– /etc/profile
– $HOME/.bash_profile
– $HOME/.bash_login
– $HOME/.profile
If you start a bash shell without logging into a system (such as if you just type bash at a CLI prompt), you start what’s called an interactive shell. The interactive shell doesn’t act like the login shell, but it still provides a CLI prompt for you to enter commands.
If bash is started as an interactive shell, it doesn’t process the /etc/profile file. Instead, it checks for the .bashrc file in the user’s HOME directory.
Finally, the last type of shell is a non-interactive shell. This is the shell that the system starts to execute a shell script. This is different in that there isn’t a CLI prompt to worry about. However, there may still be specific startup commands you want to run each time you start a script on your system.
To accommodate that situation, the bash shell provides the BASH_ENV environment variable. When the shell starts a non-interactive shell process, it checks this environment variable for the name of a startup file to execute. If one is present, the shell executes the commands in the file.
The terminfo database is a set of files that identify the characteristics of various terminals that can be used on the Linux system. The Linux system stores the terminfo data for each terminal type as a separate file in the terminfo database directory. The location of this directory often varies from distribution to distribution. Some common locations are /usr/share/terminfo, /etc/terminfo, and /lib/terminfo.
Since the terminfo database files are binary, you cannot see the codes within these files. However, you can use the infocmp command to convert the binary entries into text.
The Linux shell uses the TERM environment variable to define which terminal emulation setting in the terminfo database to use for a specific session. When the TERM environment variable is set to vt100, the shell knows to use the control codes associated with the vt100 terminfo database entry for sending control codes to the terminal emulator.
With modern Linux systems, when the Linux system starts it automatically creates several virtual consoles. A virtual console is a terminal session that runs in memory on the Linux system. Instead of having several dumb terminals connected to the PC, most Linux distributions start seven (or sometimes even more) virtual consoles that you can access from the single PC keyboard and monitor.
In most Linux distributions, you can access the virtual consoles using a simple keystroke combination. Usually you must hold down the Ctl+Alt key combination, and then press a function key (F1 through F8) for the virtual console you want to use. Function key F1 produces virtual console 1, key F2 produces virtual console 2, and so on.
There are two types of environment variables in the bash shell:
– Global variables
– Local variables
Global environment variables are visible from the shell session, and from any child processes that the shell spawns. Local variables are only available in shell that creates them. This makes global environment variables useful in applications that spawn child processes that require information from the parent process.
To view the global environment variables, use the printenv command.
To display the value of an individual environment variable, use the echo command. When referencing an environment variable, you must place a dollar sign($) before the environment variable name.
Unfortunately there isn’t a command that displays only local environment variables. The set command displays all of the environment variables set for a specific process. However, this also includes the global environment variables.
You can assign either a numeric or a string value to an environment variable by assigning the variable to a value using the equal sign(=). It’s extremely important that there are no spaces between the environment variable name, the equal sign, and the value. If you put any spaces in the assignment, the bash shell interprets the value as a separate command.
The method used to create a global environment variable is to create a local environment variable and then export it to the global environment.
Of course, if you can create a new environment variable, it makes sense that you can also remove an existing environment variable. You can do this with the unset command.When referencing the environment variable in the unset command, remember not to use the dollar sign.
NOTE: When dealing with global environment variables, things get a little tricky. If you’re in a child process and unset a global environment variable, it applies only to the child process. The global environment variable is still available in the parent process.
I used mencoder utility to convert my video files. But it was compiled without libfaac. So if you specify AAC encoding, an error occurs. Details and solutions can be found here. I just added the Medibuntu repository as described:
|
1 2 3 4 |
# sudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list # sudo apt-get --quiet update # sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring # sudo apt-get --quiet update |
NOTE: ffmpeg utility in Lucid release does not support *.rm/*.rmvb yet.
Then install mencoder and codecs:
|
1 |
# sudo apt-get install mencoder libavcodec-extra-52 libavformat-extra-52 |
Now you can convert videos. Here’s a sample to convert a *.rmvb(848×480) to a *.mp4(320×240):
|
1 |
# mencoder -oac lavc -ovc lavc -lavcopts acodec=libfaac:abitrate=96:aglobal=1:vcodec=mpeg4:vbitrate=500:vglobal=1 -vf scale=320:180,harddup -vf-add expand=:240 -ofps 24000/1001 -of lavf source.rmvb -o target.mp4 |
Modify fps/codec/bitrate values as you wish. The aglobal & vglobal options seem to be essential for iPod.
In order to keep video aspect after scaling, the output file should be 360×204. we use the -vf-add filter to add black band to the top and bottom of it. Other command line options, please refer to its manpage.
Lastly, install gtkpod to import your *.mp4 files.
Updated Mar 27, 2012: The above command line is for iPod Nano. For high quality H264 encoding used in iPod Touch or iPhone, run:
|
1 |
# mencoder -oac faac -faacopts raw:object=2:mpeg=4:br=96 -ovc x264 -x264encopts nocabac:global_header:bframes=0:level_idc=30:bitrate=600:threads=auto -vf scale=960:-2,harddup -ofps 24000/1001 -of lavf -lavfopts format=mp4 source.rmvb -o target.mp4 |