linux bash shell 基本知识

系统管理员 2022-04-12 08:08 397阅读 0赞

以下为转载内容：

$ which bash

![bash interpreter location: /bin/bash][bash interpreter location_ _bin_bash]

Open up you favorite text editor and a create file called hello\_world.sh. Insert the following lines to a file:

NOTE:Every bash shell script in this tutorial starts with **shebang:"\#!"** which is not read as a comment. First line is also a place where you put your interpreter which is in this case: /bin/bash.

Here is our first bash shell script example:

#!/bin/bash
    # declare STRING variable
    STRING="Hello World"
    #print variable on a screen
    echo $STRING

Navigate to a directory where your hello\_world.sh is located and make the file executable:

$ chmod +x hello_world.sh

![Make bash shell script executable][]

Now you are ready to execute your first bash script:

./hello_world.sh

![Example of simple bash shell script][]

# 2. Simple Backup bash shell script #

#!/bin/bash
    tar -czf myhome_directory.tar.gz /home/linuxconfig

![Simple Backup bash script][]

# 3. Variables #

In this example we declare simple bash variable and print it on the screen ( stdout ) with echo command.

#!/bin/bash
     STRING="HELLO WORLD!!!"
     echo $STRING

![Bash string Variables in bash script][]

Your backup script and variables:

#!/bin/bash
     OF=myhome_directory_$(date +%Y%m%d).tar.gz
     tar -czf $OF /home/linuxconfig

![Bash backup Script with bash Variables][]

## 3.1. Global vs. Local variables ##

#!/bin/bash
    #Define bash global variable
    #This variable is global and can be used anywhere in this bash script
    VAR="global variable"
    function bash {
    #Define bash local variable
    #This variable is local to bash function only
    local VAR="local variable"
    echo $VAR
    }
    echo $VAR
    bash
    # Note the bash global variable did not change
    # "local" is bash reserved word
    echo $VAR

![Global vs. Local Bash variables in bash script][]

# 4. Passing arguments to the bash script #

#!/bin/bash
    # use predefined variables to access passed arguments
    #echo arguments to the shell
    echo $1 $2 $3 ' -> echo $1 $2 $3'
    
    # We can also store arguments from bash command line in special array
    args=("$@")
    #echo arguments to the shell
    echo ${args[0]} ${args[1]} ${args[2]} ' -> args=("$@"); echo ${args[0]} ${args[1]} ${args[2]}'
    
    #use $@ to print out all arguments at once
    echo $@ ' -> echo $@'
    
    # use $# variable to print out
    # number of arguments passed to the bash script
    echo Number of arguments passed: $# ' -> echo Number of arguments passed: $#'

/arguments.sh Bash Scripting Tutorial

![Passing arguments to the bash script][]

# 5. Executing shell commands with bash #

#!/bin/bash
    # use backticks " ` ` " to execute shell command
    echo `uname -o`
    # executing bash command without backticks
    echo uname -o

![Executing shell commands with bash][]

# 6. Reading User Input #

#!/bin/bash
     
    echo -e "Hi, please type the word: \c "
    read  word
    echo "The word you entered is: $word"
    echo -e "Can you please enter two words? "
    read word1 word2
    echo "Here is your input: \"$word1\" \"$word2\""
    echo -e "How do you feel about bash scripting? "
    # read command now stores a reply into the default build-in variable $REPLY
    read
    echo "You said $REPLY, I'm glad to hear that! "
    echo -e "What are your favorite colours ? "
    # -a makes read command to read into an array
    read -a colours
    echo "My favorite colours are also ${colours[0]}, ${colours[1]} and ${colours[2]}:-)"

![Reading User Input with bash][]

# 7. Bash Trap Command #

<table style="border-collapse:collapse;border-spacing:0px;color:#666666;font-family:Arial;font-size:12.8000001907349px;line-height:19.2000007629395px;background-color:#f2f2f2;"> 
 <tbody> 
  <tr> 
   <td> <pre>#!/bin/bash
# bash trap command
trap bashtrap INT
# bash clear screen command
clear;
# bash trap function is executed when CTRL-C is pressed:
# bash prints message =&gt; Executing bash trap subrutine !
bashtrap()
{
    echo "CTRL+C Detected !...executing bash trap !"
}
# for loop from 1/10 to 10/10
for a in `seq 1 10`; do
    echo "$a/10 to Exit." 
    sleep 1;
done
echo "Exit Bash Trap Example!!!" </pre> </td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

# 8. Arrays #

## 8.1. Declare simple bash array ##

#!/bin/bash
    #Declare array with 4 elements
    ARRAY=( 'Debian Linux' 'Redhat Linux' Ubuntu Linux )
    # get number of elements in the array
    ELEMENTS=${#ARRAY[@]}
    
    # echo each element in array 
    # for loop
    for (( i=0;i<$ELEMENTS;i++)); do
        echo ${ARRAY[${i}]}
    done

![Declare simple bash array][]

## 8.2. Read file into bash array ##

#!/bin/bash
    # Declare array
    declare -a ARRAY
    # Link filedescriptor 10 with stdin
    exec 10<&0
    # stdin replaced with a file supplied as a first argument
    exec < $1
    let count=0
    
    while read LINE; do
    
        ARRAY[$count]=$LINE
        ((count++))
    done
    
    echo Number of elements: ${#ARRAY[@]}
    # echo array's content
    echo ${ARRAY[@]}
    # restore stdin from filedescriptor 10
    # and close filedescriptor 10
    exec 0<&10 10<&-

**Bash script execution with an output:**

linuxconfig.org $ cat bash.txt 
    Bash
    Scripting
    Tutorial
    Guide
    linuxconfig.org $ ./bash-script.sh bash.txt 
    Number of elements: 4
    Bash Scripting Tutorial Guide
    linuxconfig.org $

# 9. Bash if / else / fi statements #

## 9.1. Simple Bash if/else statement ##

Please note the spacing inside the \[ and \] brackets! Without the spaces, it won't work!

#!/bin/bash
    directory="./BashScripting"
    
    # bash check if directory exists
    if [ -d $directory ]; then
    	echo "Directory exists"
    else 
    	echo "Directory does not exists"
    fi

![Bash if else fi statement][]

## 9.2. Nested if/else ##

#!/bin/bash
     
    # Declare variable choice and assign value 4
    choice=4
    # Print to stdout
     echo "1. Bash"
     echo "2. Scripting"
     echo "3. Tutorial"
     echo -n "Please choose a word [1,2 or 3]? "
    # Loop while the variable choice is equal 4
    # bash while loop
    while [ $choice -eq 4 ]; do
     
    # read user input
    read choice
    # bash nested if/else
    if [ $choice -eq 1 ] ; then
     
            echo "You have chosen word: Bash"
    
    else                   
    
            if [ $choice -eq 2 ] ; then
                     echo "You have chosen word: Scripting"
            else
             
                    if [ $choice -eq 3 ] ; then
                            echo "You have chosen word: Tutorial"
                    else
                            echo "Please make a choice between 1-3 !"
                            echo "1. Bash"
                            echo "2. Scripting"
                            echo "3. Tutorial"
                            echo -n "Please choose a word [1,2 or 3]? "
                            choice=4
                    fi   
            fi
    fi
    done

![Nested Bash if else statement][]

# 10. Bash Comparisons #

## 10.1. Arithmetic Comparisons ##

#!/bin/bash
    # declare integers
    NUM1=2
    NUM2=2
    if [ $NUM1 -eq $NUM2 ]; then
    	echo "Both Values are equal"
    else 
    	echo "Values are NOT equal"
    fi

![Bash Arithmetic Comparisons][]

#!/bin/bash
    # declare integers
    NUM1=2
    NUM2=1
    if [ $NUM1 -eq $NUM2 ]; then
    	echo "Both Values are equal"
    else 
    	echo "Values are NOT equal"
    fi

![Bash Arithmetic Comparisons - values are NOT equal][]

#!/bin/bash
    # declare integers
    NUM1=2
    NUM2=1
    if   [ $NUM1 -eq $NUM2 ]; then
    	echo "Both Values are equal"
    elif [ $NUM1 -gt $NUM2 ]; then
    	echo "NUM1 is greater then NUM2"
    else 
    	echo "NUM2 is greater then NUM1"
    fi

![Bash Arithmetic Comparisons - greater then][]

## 10.2. String Comparisons ##

#!/bin/bash
    #Declare string S1
    S1="Bash"
    #Declare string S2
    S2="Scripting"
    if [ $S1 = $S2 ]; then
    	echo "Both Strings are equal"
    else 
    	echo "Strings are NOT equal"
    fi

![Bash String Comparisons - values are NOT equal][]

#!/bin/bash
    #Declare string S1
    S1="Bash"
    #Declare string S2
    S2="Bash"
    if [ $S1 = $S2 ]; then
    	echo "Both Strings are equal"
    else 
    	echo "Strings are NOT equal"
    fi

![bash interpreter location: /bin/bash][bash interpreter location_ _bin_bash 1]

# 11. Bash File Testing #

<table style="border-collapse:collapse;border-spacing:0px;color:#666666;font-family:Arial;font-size:12.8000001907349px;line-height:19.2000007629395px;background-color:#f2f2f2;"> 
 <tbody> 
  <tr> 
   <td>-b filename</td> 
   <td>Block special file</td> 
  </tr> 
  <tr> 
   <td>-c filename</td> 
   <td>Special character file</td> 
  </tr> 
  <tr> 
   <td>-d directoryname</td> 
   <td>Check for directory existence</td> 
  </tr> 
  <tr> 
   <td>-e filename</td> 
   <td>Check for file existence</td> 
  </tr> 
  <tr> 
   <td>-f filename</td> 
   <td>Check for regular file existence not a directory</td> 
  </tr> 
  <tr> 
   <td>-G filename</td> 
   <td>Check if file exists and is owned by effective group ID.</td> 
  </tr> 
  <tr> 
   <td>-g filename</td> 
   <td>true if file exists and is set-group-id.</td> 
  </tr> 
  <tr> 
   <td>-k filename</td> 
   <td>Sticky bit</td> 
  </tr> 
  <tr> 
   <td>-L filename</td> 
   <td>Symbolic link</td> 
  </tr> 
  <tr> 
   <td>-O filename</td> 
   <td>True if file exists and is owned by the effective user id.</td> 
  </tr> 
  <tr> 
   <td>-r filename</td> 
   <td>Check if file is a readable</td> 
  </tr> 
  <tr> 
   <td>-S filename</td> 
   <td>Check if file is socket</td> 
  </tr> 
  <tr> 
   <td>-s filename</td> 
   <td>Check if file is nonzero size</td> 
  </tr> 
  <tr> 
   <td>-u filename</td> 
   <td>Check if file set-ser-id bit is set</td> 
  </tr> 
  <tr> 
   <td>-w filename</td> 
   <td>Check if file is writable</td> 
  </tr> 
  <tr> 
   <td>-x filename</td> 
   <td>Check if file is executable</td> 
  </tr> 
 </tbody> 
</table>

#!/bin/bash
    file="./file"
    if [ -e $file ]; then
    	echo "File exists"
    else 
    	echo "File does not exists"
    fi

![Bash File Testing - File does not exist][] ![Bash File Testing - File exists][]

Similarly for example we can use while loop to check if file does not exists. This script will sleep until file does exists. Note bash negator "!" which negates the -e option.

#!/bin/bash
     
    while [ ! -e myfile ]; do
    # Sleep until file does exists/is created
    sleep 1
    done

# 12. Loops #

## 12.1. Bash for loop ##

#!/bin/bash
    
    # bash for loop
    for f in $( ls /var/ ); do
    	echo $f
    done

Running for loop from bash shell command line:

$ for f in $( ls /var/ ); do echo $f; done

![Bash for loop][]

## 12.2. Bash while loop ##

#!/bin/bash
    COUNT=6
    # bash while loop
    while [ $COUNT -gt 0 ]; do
    	echo Value of count is: $COUNT
    	let COUNT=COUNT-1
    done

![Bash while loop][]

## 12.3. Bash until loop ##

#!/bin/bash
    COUNT=0
    # bash until loop
    until [ $COUNT -gt 5 ]; do
            echo Value of count is: $COUNT
            let COUNT=COUNT+1
    done

![Bash until loop][]

## 12.4. Control bash loop with ##

Here is a example of while loop controlled by standard input. Until the redirection chain from STDOUT to STDIN to the read command exists the while loop continues.

#!/bin/bash
    # This bash script will locate and replace spaces
    # in the filenames
    DIR="."
    # Controlling a loop with bash read command by redirecting STDOUT as
    # a STDIN to while loop
    # find will not truncate filenames containing spaces
    find $DIR -type f | while read file; do
    # using POSIX class [:space:] to find space in the filename
    if [[ "$file" = *[[:space:]]* ]]; then
    # substitute space with "_" character and consequently rename the file
    mv "$file" `echo $file | tr ' ' '_'`
    fi;
    # end of while loop
    done

![Bash script to replace spaces in the filenames with \_][Bash script to replace spaces in the filenames with]

# 13. Bash Functions #

!/bin/bash
    # BASH FUNCTIONS CAN BE DECLARED IN ANY ORDER
    function function_B {
            echo Function B.
    }
    function function_A {
            echo $1
    }
    function function_D {
            echo Function D.
    }
    function function_C {
            echo $1
    }
    # FUNCTION CALLS
    # Pass parameter to function A
    function_A "Function A."
    function_B
    # Pass parameter to function C
    function_C "Function C."
    function_D

![Bash Functions][]

# 14. Bash Select #

#!/bin/bash
     
    PS3='Choose one word: ' 
    
    # bash select
    select word in "linux" "bash" "scripting" "tutorial" 
    do
      echo "The word you have selected is: $word"
    # Break, otherwise endless loop
      break  
    done
    
    exit 0

![Bash Select][]

# 15. Case statement conditional #

#!/bin/bash
    echo "What is your preferred programming / scripting language"
    echo "1) bash"
    echo "2) perl"
    echo "3) phyton"
    echo "4) c++"
    echo "5) I do not know !"
    read case;
    #simple case bash structure
    # note in this case $case is variable and does not have to
    # be named case this is just an example
    case $case in
        1) echo "You selected bash";;
        2) echo "You selected perl";;
        3) echo "You selected phyton";;
        4) echo "You selected c++";;
        5) exit
    esac

![bash case statement conditiona][]

# 16. Bash quotes and quotations #

Quotations and quotes are important part of bash and bash scripting. Here are some bash quotes and quotations basics.

## 16.1. Escaping Meta characters ##

Before we start with quotes and quotations we should know something about escaping meta characters. Escaping will suppress a special meaning of meta characters and therefore meta characters will be read by bash literally. To do this we need to use backslash "\\" character. Example:

#!/bin/bash
     
    #Declare bash string variable
    BASH_VAR="Bash Script"
    
    # echo variable BASH_VAR
    echo $BASH_VAR
    
    #when meta character such us "$" is escaped with "\" it will be read literally
    echo \$BASH_VAR 
    
    # backslash has also special meaning and it can be suppressed with yet another "\"
    echo "\\"

![escaping meta characters in bash][]

## 16.2. Single quotes ##

Single quotes in bash will suppress special meaning of every meta characters. Therefore meta characters will be read literally. It is not possible to use another single quote within two single quotes not even if the single quote is escaped by backslash.

#!/bin/bash
     
     #Declare bash string variable
     BASH_VAR="Bash Script"
     
     # echo variable BASH_VAR
     echo $BASH_VAR
     
     # meta characters special meaning in bash is suppressed when  using single quotes 
     echo '$BASH_VAR  "$BASH_VAR"'

![Using single quotes in bash][]

## 16.3. Double Quotes ##

Double quotes in bash will suppress special meaning of every meta characters except "$", "\\" and "\`". Any other meta characters will be read literally. It is also possible to use single quote within double quotes. If we need to use double quotes within double quotes bash can read them literally when escaping them with "\\". Example:

#!/bin/bash
     
    #Declare bash string variable
    BASH_VAR="Bash Script"
    
    # echo variable BASH_VAR
    echo $BASH_VAR
    
    # meta characters and its special meaning in bash is 
    # suppressed when using double quotes except "$", "\" and "`"
    
    echo "It's $BASH_VAR  and \"$BASH_VAR\" using backticks: `date`"

![Using double quotes in bash][]

## 16.4. Bash quoting with ANSI-C style ##

There is also another type of quoting and that is ANSI-C. In this type of quoting characters escaped with "\\" will gain special meaning according to the ANSI-C standard.

The syntax fo ansi-c bash quoting is: $'' . Here is an example:

#!/bin/bash
     
    # as a example we have used \n as a new line, \x40 is hex value for @
    # and \56 is octal value for .
    echo $'web: www.linuxconfig.org\nemail: web\x40linuxconfig\56org'

![quoting in bash with ansi-c stype][]

# 17. Arithmetic Operations #

## 17.1. Bash Addition Calculator Example ##

#!/bin/bash
     
    let RESULT1=$1+$2
    echo $1+$2=$RESULT1 ' -> # let RESULT1=$1+$2'
    declare -i RESULT2
    RESULT2=$1+$2
    echo $1+$2=$RESULT2 ' -> # declare -i RESULT2; RESULT2=$1+$2'
    echo $1+$2=$(($1 + $2)) ' -> # $(($1 + $2))'

![Bash Addition Calculator][]

## 17.2. Bash Arithmetics ##

#!/bin/bash
     
    echo '### let ###'
    # bash addition
    let ADDITION=3+5
    echo "3 + 5 =" $ADDITION
    
    # bash subtraction
    let SUBTRACTION=7-8
    echo "7 - 8 =" $SUBTRACTION 
    
    # bash multiplication
    let MULTIPLICATION=5*8
    echo "5 * 8 =" $MULTIPLICATION
    
    # bash division
    let DIVISION=4/2
    echo "4 / 2 =" $DIVISION
    
    # bash modulus
    let MODULUS=9%4
    echo "9 % 4 =" $MODULUS
    
    # bash power of two
    let POWEROFTWO=2**2
    echo "2 ^ 2 =" $POWEROFTWO
    
    
    echo '### Bash Arithmetic Expansion ###'
    # There are two formats for arithmetic expansion: $[ expression ] 
    # and $(( expression #)) its your choice which you use
    
    echo 4 + 5 = $((4 + 5))
    echo 7 - 7 = $[ 7 - 7 ]
    echo 4 x 6 = $((3 * 2))
    echo 6 / 3 = $((6 / 3))
    echo 8 % 7 = $((8 % 7))
    echo 2 ^ 8 = $[ 2 ** 8 ]
    
    
    echo '### Declare ###'
    
    echo -e "Please enter two numbers \c"
    # read user input
    read num1 num2
    declare -i result
    result=$num1+$num2
    echo "Result is:$result "
    
    # bash convert binary number 10001
    result=2#10001
    echo $result
    
    # bash convert octal number 16
    result=8#16
    echo $result
    
    # bash convert hex number 0xE6A
    result=16#E6A
    echo $result

![Bash Arithmetic Operations][]

## 17.3. Round floating point number ##

#!/bin/bash
    # get floating point number
    floating_point_number=3.3446
    echo $floating_point_number
    # round floating point number with bash
    for bash_rounded_number in $(printf %.0f $floating_point_number); do
    echo "Rounded number with bash:" $bash_rounded_number
    done

![Round floating point number with bash][]

## 17.4. Bash floating point calculations ##

#!/bin/bash
    # Simple linux bash calculator 
    echo "Enter input:" 
    read userinput
    echo "Result with 2 digits after decimal point:"
    echo "scale=2; ${userinput}" | bc 
    echo "Result with 10 digits after decimal point:"
    echo "scale=10; ${userinput}" | bc 
    echo "Result as rounded integer:"
    echo $userinput | bc

![Bash floating point calculations][]

# 18. Redirections #

## 18.1. STDOUT from bash script to STDERR ##

#!/bin/bash
     
     echo "Redirect this STDOUT to STDERR" 1>&2

To prove that STDOUT is redirected to STDERR we can redirect script's output to file:  
![STDOUT from bash script to STDERR][]

## 18.2. STDERR from bash script to STDOUT ##

#!/bin/bash
     
     cat $1 2>&1

To prove that STDERR is redirected to STDOUT we can redirect script's output to file:  
![STDERR from bash script to STDOUT][]

## 18.3. stdout to screen ##

The simple way to redirect a standard output ( stdout ) is to simply use any command, because by default stdout is automatically redirected to screen. First create a file "file1":

$ touch file1
    $ ls file1 
    file1

As you can see from the example above execution of ls command produces STDOUT which by default is redirected to screen.

## 18.4. stdout to file ##

The override the default behavior of STDOUT we can use ">" to redirect this output to file:

$ ls file1 > STDOUT
    $ cat STDOUT 
    file1

## 18.5. stderr to file ##

By default STDERR is displayed on the screen:

$ ls
    file1  STDOUT
    $ ls file2
    ls: cannot access file2: No such file or directory

In the following example we will redirect the standard error ( stderr ) to a file and stdout to a screen as default. Please note that STDOUT is displayed on the screen, however STDERR is redirected to a file called STDERR:

$ ls
    file1  STDOUT
    $ ls file1 file2 2> STDERR
    file1
    $ cat STDERR 
    ls: cannot access file2: No such file or directory

## 18.6. stdout to stderr ##

It is also possible to redirect STDOUT and STDERR to the same file. In the next example we will redirect STDOUT to the same descriptor as STDERR. Both STDOUT and STDERR will be redirected to file "STDERR\_STDOUT".

$ ls
    file1  STDERR  STDOUT
    $ ls file1 file2 2> STDERR_STDOUT 1>&2
    $ cat STDERR_STDOUT
    ls: cannot access file2: No such file or directory
    file1

File STDERR\_STDOUT now contains STDOUT and STDERR.

## 18.7. stderr to stdout ##

The above example can be reversed by redirecting STDERR to the same descriptor as SDTOUT:

$ ls
    file1  STDERR  STDOUT
    $ ls file1 file2 > STDERR_STDOUT 2>&1
    $ cat STDERR_STDOUT 
    ls: cannot access file2: No such file or directory
    file1

## 18.8. stderr and stdout to file ##

Previous two examples redirected both STDOUT and STDERR to a file. Another way to achieve the same effect is illustrated below:

$ ls
    file1  STDERR  STDOUT
    $ ls file1 file2 &> STDERR_STDOUT
    $ cat STDERR_STDOUT 
    ls: cannot access file2: No such file or directory
    file1

ls file1 file2 >& STDERR_STDOUT
    $ cat STDERR_STDOUT 
    ls: cannot access file2: No such file or directory
    file1

转载自：http://linuxconfig.org/bash-scripting-tutorial

[bash interpreter location_ _bin_bash]: http://linuxconfig.org/images/locate-bash-interpreter.gif
[Make bash shell script executable]: http://linuxconfig.org/images/make-bash-script-executable.gif
[Example of simple bash shell script]: http://linuxconfig.org/images/Hellobash.gif
[Simple Backup bash script]: http://linuxconfig.org/images/Bash-Simple-backup-script-example.gif
[Bash string Variables in bash script]: http://linuxconfig.org/images/Bash-string-Variables-bash-script.gif
[Bash backup Script with bash Variables]: http://linuxconfig.org/images/Bash-backup-Script-bash-variables.gif
[Global vs. Local Bash variables in bash script]: http://linuxconfig.org/images/Bash-global-local-bash-variables-bash-script.gif
[Passing arguments to the bash script]: http://linuxconfig.org/images/Passing-arguments-bash-script.gif
[Executing shell commands with bash]: http://linuxconfig.org/images/Execute-shell-commands-within-bash-script.gif
[Reading User Input with bash]: http://linuxconfig.org/images/Reading-user-input-bash-script.gif
[Declare simple bash array]: http://linuxconfig.org/images/declare-bash-array.gif
[Bash if else fi statement]: http://linuxconfig.org/images/bash-if-else-fi-statement.gif
[Nested Bash if else statement]: http://linuxconfig.org/images/bash-if-else-nested-statement.gif
[Bash Arithmetic Comparisons]: http://linuxconfig.org/images/bash_arithmetic-comparisons-equal.gif
[Bash Arithmetic Comparisons - values are NOT equal]: http://linuxconfig.org/images/bash_arithmetic-comparisons-not-equal.gif
[Bash Arithmetic Comparisons - greater then]: http://linuxconfig.org/images/bash_arithmetic-comparisons-greater-then.gif
[Bash String Comparisons - values are NOT equal]: http://linuxconfig.org/images/bash-string-comparisons-values-NOT-equal.gif
[bash interpreter location_ _bin_bash 1]: http://linuxconfig.org/images/bash-string-comparisons-values-equal.gif
[Bash File Testing - File does not exist]: http://linuxconfig.org/images/bash-file-testing-file-does-not-exist.gif
[Bash File Testing - File exists]: http://linuxconfig.org/images/bash-file-testing-file-exist.gif
[Bash for loop]: http://linuxconfig.org/images/bash-for-loop.gif
[Bash while loop]: http://linuxconfig.org/images/bash-while-loop.gif
[Bash until loop]: http://linuxconfig.org/images/bash-until-loop.gif
[Bash script to replace spaces in the filenames with]: http://linuxconfig.org/images/Rename_files_containing_spaces.gif
[Bash Functions]: http://linuxconfig.org/images/bash-functions.gif
[Bash Select]: http://linuxconfig.org/images/bash_select.gif
[bash case statement conditiona]: http://linuxconfig.org/images/Bash_case_statement.gif
[escaping meta characters in bash]: http://linuxconfig.org/images/Escaping_meta.gif
[Using single quotes in bash]: http://linuxconfig.org/images/Bash_single_quotes.gif
[Using double quotes in bash]: http://linuxconfig.org/images/Bash_double_quotes.gif
[quoting in bash with ansi-c stype]: http://linuxconfig.org/images/Ansi-c_bash.gif
[Bash Addition Calculator]: http://linuxconfig.org/images/Bash_addition_calc.gif
[Bash Arithmetic Operations]: http://linuxconfig.org/images/bash-arithmetic_operations.gif
[Round floating point number with bash]: http://linuxconfig.org/images/Bash_round_floating_point_number.gif
[Bash floating point calculations]: http://linuxconfig.org/images/Bash_floating_point.gif
[STDOUT from bash script to STDERR]: http://linuxconfig.org/images/STDOUTtoSTDERR.gif
[STDERR from bash script to STDOUT]: http://linuxconfig.org/images/STDERRtoSTDOUT.gif