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-
-
-
-BASH Programming - Introduction HOW-TO
-
-
-
-----
-
-!!!BASH Programming - Introduction HOW-TO
-
-!!by Mike G mikkey at dynamo.com.ar Thu Jul 27 09:36:18 ART 2000
-
-
-----
-'' This article intends to help you to start programming basic-intermediate shell scripts. It does not intend to be an advanced document (see the title). I am NOT an expert nor guru shell programmer. I decided to write this because I'll learn a lot and it might be useful to other people. Any feedback will be apreciated, specially in the patch form :) ''
-----
-
-
-
-
-!!1. Introduction
-
-
-*1.1 Getting the latest version
-
-*1.2 Requisites
-
-*1.3 Uses of this document
-
-
-
-
-
-!!2. Very simple Scripts
-
-
-*2.1 Traditional hello world script
-
-*2.2 A very simple backup script
-
-
-
-
-
-!!3. All about redirection
-
-
-*3.1 Theory and quick reference
-
-*3.2 Sample: stdout 2 file
-
-*3.3 Sample: stderr 2 file
-
-*3.4 Sample: stdout 2 stderr
-
-*3.5 Sample: stderr 2 stdout
-
-*3.6 Sample: stderr and stdout 2 file
-
-
-
-
-
-!!4. Pipes
-
-
-*4.1 What they are and why you'll want to use them
-
-*4.2 Sample: simple pipe with sed
-
-*4.3 Sample: an alternative to ls -l *.txt
-
-
-
-
-
-!!5. Variables
-
-
-*5.1 Sample: Hello World! using variables
-
-*5.2 Sample: A very simple backup script (little bit better)
-
-*5.3 Local variables
-
-
-
-
-
-!!6. Conditionals
-
-
-*6.1 Dry Theory
-
-*6.2 Sample: Basic conditional example if .. then
-
-*6.3 Sample: Basic conditional example if .. then ... else
-
-*6.4 Sample: Conditionals with variables
-
-
-
-
-
-!!7. Loops for, while and until
-
-
-*7.1 For sample
-
-*7.2 C-like for
-
-*7.3 While sample
-
-*7.4 Until sample
-
-
-
-
-
-!!8. Functions
-
-
-*8.1 Functions sample
-
-*8.2 Functions with parameters sample
-
-
-
-
-
-!!9. User interfaces
-
-
-*9.1 Using select to make simple menus
-
-*9.2 Using the command line
-
-
-
-
-
-!!10. Misc
-
-
-*10.1 Reading user input with read
-
-*10.2 Arithmetic evaluation
-
-*10.3 Finding bash
-
-*10.4 Getting the return value of a program
-
-*10.5 Capturing a commands output
-
-*10.6 Multiple source files
-
-
-
-
-
-!!11. Tables
-
-
-*11.1 String comparison operators
-
-*11.2 String comparison examples
-
-*11.3 Arithmetic operators
-
-*11.4 Arithmetic relational operators
-
-*11.5 Useful commands
-
-
-
-
-
-!!12. More Scripts
-
-
-*12.1 Applying a command to all files in a directory.
-
-*12.2 Sample: A very simple backup script (little bit better)
-
-*12.3 File re-namer
-
-*12.4 File renamer (simple)
-
-
-
-
-
-!!13. When something goes wrong (debugging)
-
-
-*13.1 Ways Calling BASH
-
-
-
-
-
-!!14. About the document
-
-
-*14.1 (no) warranty
-
-*14.2 Translations
-
-*14.3 Thanks to
-
-*14.4 History
-
-*14.5 More resources
-
-----
-
-!!1. Introduction
-
-!!1.1 Getting the latest version
-
-
-
-
-http://www.linuxdoc.org/HOWTO/Bash-Prog-Intro-HOWTO.html
-
-
-
-
-
-
-!!1.2 Requisites
-
-
-
- Familiarity with GNU/Linux command lines, and familiarity
-with basic programming concepts is helpful. While this is not
-a programming introduction, it explains (or at least tries) many
-basic concepts.
-
-
-
-
-!!1.3 Uses of this document
-
-
-
- This document tries to be useful in the following situations
-
-
-* You have an idea about programming and you want to start
-coding some shell scripts.
-*
-
-* You have a vague idea about shell programming and want
-some sort of reference.
-*
-
-* You want to see some shell scripts and some comments to
-start writing your own
-*
-
-* You are migrating from DOS/Windows (or already did)
-and want to make "batch" processes.
-*
-
-* You are a complete nerd and read every how-to available
-*
-
-----
-
-!!2. Very simple Scripts
-
-
- This HOW-TO will try to give you some hints about shell script
-programming strongly based on examples.
-
-
- In this section you'll find some little scripts which
-will hopefully help you to understand some techniques.
-
-
-
-
-!!2.1 Traditional hello world script
-
-
-
-
-
-
-#!/bin/bash
-echo Hello World
-
-
-
-
-
-
-
- This script has only two lines.
-The first indicates the system which program
-to use to run the file.
-
-
- The second line is the only action performed by this script,
-which prints 'Hello World' on the terminal.
-
-
- If you get something like ''./hello.sh: Command not found.''
-Probably the first line '#!/bin/bash' is wrong, issue whereis bash or see
-'finding bash' to see how sould you write this line.
-
-!!2.2 A very simple backup script
-
-
-
-
-
-
-#!/bin/bash
-tar -cZf /var/my-backup.tgz /home/me/
-
-
-
-
- In this script, instead of printing a message on the terminal,
-we create a tar-ball of a user's home directory. This is NOT intended
-to be used, a more useful backup script is presented later in this
-document.
-----
-
-!!3. All about redirection
-
-!!3.1 Theory and quick reference
-
-
-
- There are 3 file descriptors, stdin, stdout and stderr (std=standard).
-
-
-
-
-
-Basically you can:
-
-
-# redirect stdout to a file
-#
-
-# redirect stderr to a file
-#
-
-# redirect stdout to a stderr
-#
-
-# redirect stderr to a stdout
-#
-
-# redirect stderr and stdout to a file
-#
-
-# redirect stderr and stdout to stdout
-#
-
-# redirect stderr and stdout to stderr
-#
-
-1 'represents' stdout and 2 stderr.
-
-
- A little note for seeing this things: with the less command you can view both stdout
-(which will remain on the buffer) and the stderr that will be printed on the screen, but erased as
-you try to 'browse' the buffer.
-
-!!3.2 Sample: stdout 2 file
-
-
-
- This will cause the ouput of a program to be written to a file.
-
-
-ls -l > ls-l.txt
-
-
-Here, a file called 'ls-l.txt' will be created and it will contain what you would see on the
-screen if you type the command 'ls -l' and execute it.
-
-!!3.3 Sample: stderr 2 file
-
-
-
- This will cause the stderr ouput of a program to be written to a file.
-
-
-grep da * 2> grep-errors.txt
-
-
-Here, a file called 'grep-errors.txt' will be created and it will contain what you would see
-the stderr portion of the output of the 'grep da *' command.
-
-!!3.4 Sample: stdout 2 stderr
-
-
-
- This will cause the stderr ouput of a program to be written to the same filedescriptor
-than stdout.
-
-
-grep da * 1>&2
-
-
-Here, the stdout portion of the command is sent to stderr, you may notice that in differen ways.
-
-!!3.5 Sample: stderr 2 stdout
-
-
-
- This will cause the stderr ouput of a program to be written to the same filedescriptor
-than stdout.
-
-
-grep * 2>&1
-
-
-Here, the stderr portion of the command is sent to stdout, if you pipe to less, you'll see that
-lines that normally 'dissapear' (as they are written to stderr) are being kept now (because
-they're on stdout).
-
-!!3.6 Sample: stderr and stdout 2 file
-
-
-
- This will place every output of a program to a file. This is suitable sometimes
-for cron entries, if you want a command to pass in absolute silence.
-
-
-rm -f $(find / -name core) &> /dev/null
-
-
-This (thinking on the cron entry) will delete every file called 'core' in any directory. Notice
-that you should be pretty sure of what a command is doing if you are going to wipe it's output.
-----
-
-!!4. Pipes
-
-
- This section explains in a very simple and practical way how to use pipes,
-nd why you may want it.
-
-
-
-
-!!4.1 What they are and why you'll want to use them
-
-
-
- Pipes let you use (very simple, I insist) the output of a program as the
-input of another one
-
-!!4.2 Sample: simple pipe with sed
-
-
-
- This is very simple way to use pipes.
-
-
-ls -l | sed -e "s/
[[aeio
]/u/g"
-
-
-Here, the following happens: first the command ls -l is executed, and it's output,
-instead of being printed, is sent (piped) to the sed program, which in turn, prints
-what it has to.
-
-!!4.3 Sample: an alternative to ls -l *.txt
-
-
-
- Probably, this is a more difficult way to do ls -l *.txt, but it is
here for illustrating pipes,
-not for solving such listing dilema.
-
-
-ls -l | grep "\.txt$"
-
-
-Here, the output of the program ls -l is sent to the grep program, which, in turn, will print
-lines which match the regex "\.txt$".
-----
-
-!!5. Variables
-
-
- You can use variables as in any programming languages.
-There are no data types. A variable in bash can contain a number, a
-character, a string of characters.
-
-
- You have no need to declare a variable, just
-assigning a value to its reference will create it.
-
-
-
-
-
-
-
-
-
-
-!!5.1 Sample: Hello World! using variables
-
-
-
-
-
-
-#!/bin/bash
-STR="Hello World!"
-echo $STR
-
-
-
-
-
-
-
- Line 2 creates
-a variable called STR and assigns the string "Hello World!" to
-it. Then the VALUE of this variable is retrieved by putting
-the '$' in at the beginning. Please notice (try it!)
-that if you don't use the '$' sign, the output of the program will
-be different, and probably not what you want it to be.
-
-!!5.2 Sample: A very simple backup script (little bit better)
-
-
-
-
-
-
-#!/bin/bash
-OF=/var/my-backup-$(date +%Y%m%d).tgz
-tar -cZf $OF /home/me/
-
-
-
-
- This script introduces another thing. First
-of all, you should be familiarized with the variable
-creation and assignation on line 2. Notice the expression
-'$(date +%Y%m%d)'.
-If you run the script you'll notice that
-it runs the
-command inside the parenthesis, capturing its output.
-
-
-
-
-
- Notice that in this script, the output filename will
-be different every day, due to the format switch to the date command(+%Y%m%d).
-You can change this by specifying a different format.
-
-
- Some more examples:
-
-
- echo ls
-
-
- echo $(ls)
-
-!!5.3 Local variables
-
-
-
- Local variables can be created by using the keyword ''local''.
-
-
-
-
-
-#!/bin/bash
-HELLO=Hello
-function hello {
-local HELLO=World
-echo $HELLO
-}
-echo $HELLO
-hello
-echo $HELLO
-
-
-
-
- This example should be enought to show how to use a local variable.
-----
-
-!!6. Conditionals
-
-
- Conditionals let you decide whether to perform an action
-or not, this decision is taken by evaluating an expression.
-
-
-
-
-!!6.1 Dry Theory
-
-
-
- Conditionals have many forms. The most basic form is:
-__if__ ''expression'' __then__ ''statement''
-where 'statement' is only executed if 'expression'
-evaluates to true.
-'2<1' is an expresion that evaluates to false, while '2>1'
-evaluates to true.xs
-
-
- Conditionals have other forms such as:
-__if__ ''expression''
-__then__ ''statement1'' __else__ ''statement2''.
-Here 'statement1' is executed if 'expression' is true,otherwise
-'statement2' is executed.
-
-
- Yet another form of conditionals is:
-__if__ ''expression1''
-__then__ ''statement1''
-__else if__ ''expression2'' __then__ ''statement2''
-__else__ ''statement3''.
-In this form there's added only the
-"ELSE IF 'expression2' THEN 'statement2'" which makes statement2 being
-executed if expression2 evaluates to true. The rest is as you may
-imagine (see previous forms).
-
-
- A word about syntax:
-
-
- The base for the 'if' constructions in bash is this:
-
-
- if [[expression];
-
-
- then
-
-
- code if 'expression' is true.
-
-
- fi
-
-!!6.2 Sample: Basic conditional example if .. then
-
-
-
-
-
-
-#!/bin/bash
-if [[ "foo" = "foo" ]; then
-echo expression evaluated as true
-fi
-
-
-
-
- The code to be executed if the expression within braces
-is true can
-be found after the 'then' word and before 'fi' which indicates the end
-of the conditionally executed code.
-
-!!6.3 Sample: Basic conditional example if .. then ... else
-
-
-
-
-
-
-#!/bin/bash
-if [[ "foo" = "foo" ]; then
-echo expression evaluated as true
-else
-echo expression evaluated as false
-fi
-
-
-
-!!6.4 Sample: Conditionals with variables
-
-
-
-
-
-
-#!/bin/bash
-T1="foo"
-T2="bar"
-if [[ "$T1" = "$T2" ]; then
-echo expression evaluated as true
-else
-echo expression evaluated as false
-fi
-
-
-----
-
-!!7. Loops for, while and until
-
-
- In this section you'll find for, while and until loops.
-
-
- The __for__ loop is a little bit different from other programming
-languages. Basically, it let's you iterate over a series of
-'words' within a string.
-
-
- The __while__ executes a piece of code if the control expression
-is true, and only stops when it is false (or a explicit break is found
-within the executed code.
-
-
- The __until__ loop is almost equal to the while loop, except that
-the code is executed while the control expression evaluates to false.
-
-
- If you suspect that while and until are very similar you are right.
-
-!!7.1 For sample
-
-
-
-
-
-
-#!/bin/bash
-for i in $( ls ); do
-echo item: $i
-done
-
-
-
-
-
-
-
- On the second line, we declare i to be the variable that
-will take the
-different values contained in $( ls ).
-
-
- The third line could be longer if needed, or there could
-be more lines
-before the done (4).
-
-
- 'done' (4) indicates that the code that used the value of $i has
-finished and $i can take a new value.
-
-
- This script has very little sense, but a more useful way to use the
-for loop would be to use it to match only certain files on the previous
-example
-
-
-
-
-!!7.2 C-like for
-
-
-
- fiesh suggested adding this form of looping. It's a for loop
-more similar to C/perl... for.
-
-
-#!/bin/bash
-for i in `seq 1 10`;
-do
-echo $i
-done
-
-
-
-!!7.3 While sample
-
-
-
-
-
-
-#!/bin/bash
-COUNTER=
-while [[ $COUNTER -lt 10 ]; do
-echo The counter is $COUNTER
-let COUNTER=COUNTER+1
-done
-
-
-
-
-
-
-
- This script 'emulates' the well known
-(C, Pascal, perl, etc) 'for' structure
-
-!!7.4 Until sample
-
-
-
-
-
-
-#!/bin/bash
-COUNTER=20
-until [[ $COUNTER -lt 10 ]; do
-echo COUNTER $COUNTER
-let COUNTER-=1
-done
-
-
-----
-
-!!8. Functions
-
-
- As in almost any programming language, you can use functions to group
-pieces of code in a more logical way or practice the divine art of recursion.
-
-
- Declaring a function is just a matter of writing function my_func { my_code }.
-
-
- Calling a function is just like calling another program, you just write its name.
-
-
-
-
-!!8.1 Functions sample
-
-
-
-
-
-
-#!/bin/bash
-function quit {
-exit
-}
-function hello {
-echo Hello!
-}
-hello
-quit
-echo foo
-
-
-
-
- Lines 2-4 contain the 'quit' function. Lines 5-7 contain the 'hello' function
-If you are not absolutely sure about what this script does, please try it!.
-
-
- Notice that a functions don't need to be declared in any specific order.
-
-
- When running the script you'll notice that first: the function 'hello' is
-called, second the 'quit' function, and the program never reaches line 10.
-
-!!8.2 Functions with parameters sample
-
-
-
-
-
-
-#!/bin/bash
-function quit {
-exit
-}
-function e {
-echo $1
-}
-e Hello
-e World
-quit
-echo foo
-
-
-
-
- This script is almost identically to the previous one. The main difference is the
-funcion 'e'. This function, prints the first argument it receives.
-Arguments, within funtions, are treated in the same manner as arguments given to the script.
-----
-
-!!9. User interfaces
-
-!!9.1 Using select to make simple menus
-
-
-
-
-
-
-#!/bin/bash
-OPTIONS="Hello Quit"
-select opt in $OPTIONS; do
-if [[ "$opt" = "Quit" ]; then
-echo done
-exit
-elif [[ "$opt" = "Hello" ]; then
-echo Hello World
-else
-clear
-echo bad option
-fi
-done
-
-
-
-
- If you run this script you'll see that it is a
-programmer's dream for text based menus. You'll probably notice
-that it's very similar to the 'for' construction, only rather
-than looping for each 'word' in $OPTIONS, it prompts the user.
-
-
-
-
-!!9.2 Using the command line
-
-
-
-
-
-
-#!/bin/bash
-if [[ -z "$1" ]; then
-echo usage: $0 directory
-exit
-fi
-SRCD=$1
-TGTD="/var/backups/"
-OF=home-$(date +%Y%m%d).tgz
-tar -cZf $TGTD$OF $SRCD
-
-
-
-
-
-
-
- What this script does should be clear to you. The expression
-in the first conditional tests if the program has received an argument
-($1) and quits if it didn't, showing the user a little usage message.
-The rest of the script should be clear at this point.
-----
-
-!!10. Misc
-
-!!10.1 Reading user input with read
-
-
-
- In many ocations you may want to prompt the user for some input, and
-there are several ways
-to achive this. This is one of those ways:
-
-
-#!/bin/bash
-echo Please, enter your name
-read NAME
-echo "Hi $NAME!"
-
-
-
-
- As a variant, you can get multiple values with read, this example may
-clarify this.
-
-
-#!/bin/bash
-echo Please, enter your firstname and lastname
-read FN LN
-echo "Hi! $LN, $FN !"
-
-
-
-
-
-
-!!10.2 Arithmetic evaluation
-
-
-
- On the command line (or a shell) try this:
-
-
- echo 1 + 1
-
-
- If you expected to see '2' you'll be disappointed. What if
-you want BASH to evaluate some numbers you have? The solution
-is this:
-
-
- echo $((1+1))
-
-
- This will produce a more 'logical' output. This is to evaluate an
-arithmetic expression. You can achieve this also like this:
-
-
- echo $[[1+1]
-
-
-
-
-
- If you need to use fractions, or more math or you just want it, you
-can use bc to evaluate arithmetic expressions.
-
-
- if i ran "echo $[[3/4]" at the command prompt, it would return
-because bash only uses integers when answering. If you ran
-"echo 3/4|bc -l", it would properly return .75.
-
-!!10.3 Finding bash
-
-
-
- From a message from mike (see Thanks to)
-
-
- you always use #!/bin/bash .. you might was to give an example of
-
-
- how to find where bash is located.
-
-
- 'locate bash' is preferred, but not all machines have locate.
-
-
- 'find ./ -name bash' from the root dir will work, usually.
-
-
- Suggested locations to check:
-
-
- ls -l /bin/bash
-
-
- ls -l /sbin/bash
-
-
- ls -l /usr/local/bin/bash
-
-
- ls -l /usr/bin/bash
-
-
- ls -l /usr/sbin/bash
-
-
- ls -l /usr/local/sbin/bash
-
-
- (can't think of any other dirs offhand... i've found it in
-
-
- most of these places before on different system).
-
-
- You may try also 'which bash'.
-
-!!10.4 Getting the return value of a program
-
-
-
- In bash, the return value of a program is stored in a special variable called $?.
-
-
- This illustrates how to capture the return value of a program, I assume that the directory
-''dada'' does not exist. (This was also suggested by mike)
-
-
-#!/bin/bash
-cd /dada &> /dev/null
-echo rv: $?
-cd $(pwd) &> /dev/null
-echo rv: $?
-
-
-
-!!10.5 Capturing a commands output
-
-
-
- This little scripts show all tables from all databases (assuming you got MySQL installed).
-Also, consider changing the 'mysql' command to use a valid username and password.
-
-
-#!/bin/bash
-DBS=`mysql -uroot -e"show databases"`
-for b in $DBS ;
-do
-mysql -uroot -e"show tables from $b"
-done
-
-
-
-!!10.6 Multiple source files
-
-
-
- You can use multiple files with the command source.
-
-
- __TO-DO__
-----
-
-!!11. Tables
-
-!!11.1 String comparison operators
-
-
-
- (1) s1 = s2
-
-
- (2) s1 != s2
-
-
- (3) s1 < s2
-
-
- (4) s1 > s2
-
-
- (5) -n s1
-
-
- (6) -z s1
-
-
-
-
-
- (1) s1 matches s2
-
-
- (2) s1 does not match s2
-
-
- (3) __TO-DO__
-
-
- (4) __TO-DO__
-
-
- (5) s1 is not null (contains one or more characters)
-
-
- (6) s1 is null
-
-!!11.2 String comparison examples
-
-
-
- Comparing two strings.
-
-
-#!/bin/bash
-S1='string'
-S2='String'
-if [[ $S1=$S2 ];
-then
-echo "S1('$S1') is not equal to S2('$S2')"
-fi
-if [[ $S1=$S1 ];
-then
-echo "S1('$S1') is equal to S1('$S1')"
-fi
-
-
-
-
- I quote here a note from a mail, sent buy Andreas Beck, refering to use
-''if [[ $1 = $2 ]''.
-
-
- This is not quite a good idea, as if either $S1 or $S2 is empty, you will
-get a parse error. x$1=x$2 or "$1"="$2" is better.
-
-
-
-
-!!11.3 Arithmetic operators
-
-
-
- +
-
-
- -
-
-
- *
-
-
- /
-
-
- % (remainder)
-
-!!11.4 Arithmetic relational operators
-
-
-
- -lt (<)
-
-
- -gt (>)
-
-
- -le (<=)
-
-
- -ge (>=)
-
-
- -eq (==)
-
-
- -ne (!=)
-
-
- C programmer's should simple map the operator to its corresponding
-parenthesis.
-
-!!11.5 Useful commands
-
-
-
- This section was re-written by Kees (see thank to...)
-
-
- Some of these command's almost contain complete programming languages.
-From those commands only the basics will be explained. For a more detailed
-description, have a closer look at the man pages of each command.
-
-
-__sed__ (stream editor)
-
-
-
-
-
- Sed is a non-interactive editor. Instead of altering a file by moving the
-cursor on the screen, you use a script of editing instructions to sed, plus the
-name of the file to edit. You can also describe sed as a filter. Let's have
-a look at some examples:
-
-
-
-
-
-$sed 's/to_be_replaced/replaced/g' /tmp/dummy
-
-
-
-
-
-
-
- Sed replaces the string 'to_be_replaced' with the string 'replaced' and
-reads from the /tmp/dummy file. The result will be sent to stdout (normally
-the console) but you can also add '> capture' to the end of the line above so
-that sed sends the output to the file 'capture'.
-
-
-
-
-
-$sed 12, 18d /tmp/dummy
-
-
-
-
-
-
-
- Sed shows all lines except lines 12 to 18. The original file is not altered by this command.
-
-
-__awk__ (manipulation of datafiles, text retrieval and processing)
-
-
-
-
-
- Many implementations of the AWK programming language exist (most known interpreters are GNU's
-gawk and 'new awk' mawk.) The principle is simple: AWK scans for a pattern, and for every
-matching pattern a action will be performed.
-
-
- Again, I've created a dummy file containing the following lines:
-
-
- ''"test123''
-
-
- ''test''
-
-
- ''tteesstt"''
-
-
-
-
-
-$awk '/test/ {print}' /tmp/dummy
-
-
-
-
- test123
-
-
-
-
-
- test
-
-
-
-
-
- The pattern AWK looks for is 'test' and the action it performs when it found a line in the file
-/tmp/dummy with the string 'test' is 'print'.
-
-
-
-
-
-$awk '/test/ {i=i+1} END {print i}' /tmp/dummy
-
-
-
-
-
-
-
- 3
-
-
-
-
-
- When you're searching for many patterns, you should replace the text between the quotes with '-f
-file.awk' so you can put all patterns and actions in 'file.awk'.
-
-
-__grep__ (print lines matching a search pattern)
-
-
-
-
-
- We've already seen quite a few grep commands in the previous chapters, that display the lines
-matching a pattern. But grep can do more.
-
-
-$grep "look for this" /var/log/messages -c
-
-
-
-
- 12
-
-
- The string "look for this" has been found 12 times in the file /var/log/messages.
-
-
-
-
-
- [[ok, this example was a fake, the /var/log/messages was tweaked :-)]
-
-
-__wc__ (counts lines, words and bytes)
-
-
-
-
-
- In the following example, we see that the output is not what we expected. The dummy file, as used
-in this example, contains the following text:
-''"bash introduction''
-'' howto test file"''
-
-
-
-
-
-$wc --words --lines --bytes /tmp/dummy
-
-
-
-
-
-
-
- 2 5 34 /tmp/dummy
-
-
-
-
-
- Wc doesn't care about the parameter order. Wc always prints them in a standard order, which is,
-as you can see: .
-
-
-__sort__ (sort lines of text files)
-
-
-
-
-
- This time the dummy file contains the following text:
-
-
- ''"b''
-
-
- ''c''
-
-
- ''a"''
-
-
-$sort /tmp/dummy
-
-
-
-
-
-
-
- This is what the output looks like:
-
-
-
-
-
- ''a''
-
-
- ''b''
-
-
- ''c''
-
-
-
-
-
- Commands shouldn't be that easy :-)
-__bc__ (a calculator programming language)
-
-
-
-
-
- Bc is accepting calculations from command line (input from file. not from redirector or pipe),
-but also from a user interface. The following demonstration shows some of the commands. Note that
-
-
- I start bc using the -q parameter to avoid a welcome message.
-
-
-
-
-
-$bc -q
-
-
-
-
-
-
-
- ''1 == 5''
-
-
- ''''
-
-
- ''.05 == .05''
-
-
- ''1''
-
-
- ''5 != 5''
-
-
- ''''
-
-
- ''2 ^ 8''
-
-
- ''256''
-
-
- ''sqrt(9)''
-
-
- ''3''
-
-
- ''while (i != 9) {''
-
-
- ''i = i + 1;''
-
-
- ''print i''
-
-
- ''}''
-
-
- ''123456789''
-
-
- ''quit''
-
-
-__tput__ (initialize a terminal or query terminfo database)
-
-
-
-
-
- A little demonstration of tput's capabilities:
-
-
-$tput cup 10 4
-
-
-
-
- The prompt appears at (y10,x4).
-
-
-$tput reset
-
-
-
-
- Clears screen and prompt appears at (y1,x1). Note that (y0,x0) is the upper left corner.
-
-
-$tput cols
-
-
-''80''
-
-
- Shows the number of characters possible in x direction.
-
-
- It it higly recommended to be familiarized with these programs (at least). There are tons of
-little programs that will let you do real magic on the command line.
-
-
- [[some samples are taken from man pages or FAQs]
-----
-
-!!12. More Scripts
-
-!!12.1 Applying a command to all files in a directory.
-
-
-
-
-
-!!12.2 Sample: A very simple backup script (little bit better)
-
-
-
-
-
-
-#!/bin/bash
-SRCD="/home/"
-TGTD="/var/backups/"
-OF=home-$(date +%Y%m%d).tgz
-tar -cZf $TGTD$OF $SRCD
-
-
-
-
-
-
-!!12.3 File re-namer
-
-
-
-
-
-
-#!/bin/sh
-# renna: rename multiple files according to several rules
-# written by felix hudson Jan - 2000
-#first check for the various 'modes' that this program has
-#if the first ($1) condition matches then we execute that portion of the
-#program and then exit
-# check for the prefix condition
-if [[ $1 = p ]; then
-#we now get rid of the mode ($1) variable and prefix ($2)
-prefix=$2 ; shift ; shift
-# a quick check to see if any files were given
-# if none then its better not to do anything than rename some non-existent
-# files!!
-if [[$1 = ]; then
-echo "no files given"
-exit
-fi
-# this for loop iterates through all of the files that we gave the program
-# it does one rename per file given
-for file in $*
-do
-mv ${file} $prefix$file
-done
-#we now exit the program
-exit
-fi
-# check for a suffix rename
-# the rest of this part is virtually identical to the previous section
-# please see those notes
-if [[ $1 = s ]; then
-suffix=$2 ; shift ; shift
-if [[$1 = ]; then
-echo "no files given"
-exit
-fi
-for file in $*
-do
-mv ${file} $file$suffix
-done
-exit
-fi
-# check for the replacement rename
-if [[ $1 = r ]; then
-shift
-# i included this bit as to not damage any files if the user does not specify
-# anything to be done
-# just a safety measure
-if [[ $# -lt 3 ] ; then
-echo "usage: renna r [[expression] [[replacement] files... "
-exit
-fi
-# remove other information
-OLD=$1 ; NEW=$2 ; shift ; shift
-# this for loop iterates through all of the files that we give the program
-# it does one rename per file given using the program 'sed'
-# this is a sinple command line program that parses standard input and
-# replaces a set expression with a give string
-# here we pass it the file name ( as standard input) and replace the nessesary
-# text
-for file in $*
-do
-new=`echo ${file} | sed s/${OLD}/${NEW}/g`
-mv ${file} $new
-done
-exit
-fi
-# if we have reached here then nothing proper was passed to the program
-# so we tell the user how to use it
-echo "usage;"
-echo " renna p [[prefix] files.."
-echo " renna s [[suffix] files.."
-echo " renna r [[expression] [[replacement] files.."
-exit
-# done!
-
-
-
-!!12.4 File renamer (simple)
-
-
-
-
-
-
-#!/bin/bash
-# renames.sh
-# basic file renamer
-criteria=$1
-re_match=$2
-replace=$3
-for i in $( ls *$criteria* );
-do
-src=$i
-tgt=$(echo $i | sed -e "s/$re_match/$replace/")
-mv $src $tgt
-done
-
-
-----
-
-!!13. When something goes wrong (debugging)
-
-!!13.1 Ways Calling BASH
-
-
-
- A nice thing to do is to add on the first line
-
-
-#!/bin/bash -x
-
-
-
-
- This will produce some intresting output information
-----
-
-!!14. About the document
-
-
- Feel free to make suggestions/corrections, or whatever you think
-it would be interesting to see in this document. I'll try to update
-it as soon as I can.
-
-!!14.1 (no) warranty
-
-
-
- This documents comes with no warranty of any kind.
-and all that
-
-!!14.2 Translations
-
-
-
- Italian: by William Ghelfi (wizzy at tiscalinet.it)
-is here
-
- French: by Laurent Martelli
-is missed
-
- Korean: Minseok Park
-http://kldp.org
-
- Korean: Chun Hye Jin
-unknown
-
- Spanish: unknow
-http://www.insflug.org
-
- I guess there are more translations, but I don't have any info of them,
-if you have it, please, mail it to me so I update this section.
-
-!!14.3 Thanks to
-
-
-
-
-
-
-* People who translated this document to other languages (previous section).
-*
-
-* Nathan Hurst for sending a lot of corrections.
-*
-
-* Jon Abbott for sending comments about evaluating arithmetic expressions.
-*
-
-* Felix Hudson for writing the ''renna'' script
-*
-
-* Kees van den Broek
-(for sending many corrections, re-writting usefull comands section)
-*
-
-* Mike (pink) made some suggestions about locating bash and testing files
-*
-
-* Fiesh make a nice suggestion for the loops section.
-*
-
-* Lion suggested to mention a common error (./hello.sh: Command not found.)
-*
-
-* Andreas Beck made several corrections and coments.
-*
-
-
-!!14.4 History
-
-
-
- New translations included and minor correcitons.
-
-
- Added the section usefull commands re-writen by Kess.
-
-
- More corrections and suggestions incorporated.
-
-
- Samples added on string comparison.
-
-
- v0.8 droped the versioning, I guess the date is enought.
-
-
- v0.7 More corrections and some old TO-DO sections written.
-
-
- v0.6 Minor corrections.
-
-
- v0.5 Added the redirection section.
-
-
- v0.4 disapperd from its location due to my ex-boss and thid doc found it's new place
-at the proper url: www.linuxdoc.org.
-
-
- prior: I don't rememeber and I didn't use rcs nor cvs :(
-
-!!14.5 More resources
-
-
-
-
-
-
- Introduction to bash (under BE)
-http://org.laol.net/lamug/beforever/bashtut.htm
-
- Bourne Shell Programming
-http://207.213.123
.70/book/
-----
+Describe
[HowToBashProgIntroHOWTO
] here.
