Bash scripting

Bash-Scripting.txt

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+-> ls :
+
+    List all the file or folder present in the current directory.
+
+        Option:
+
+        * -l :  List all the file and folder with permission, owner,
+                and group details in form of vertically alinged list.
+        
+        * -a :  Display hidden (.)dotfile as well.
+
+-> pwd :
+
+    Print the current directory, present on the terminal.
+
+-> date :
+
+    Print the current date and time.
+
+-> chmod :
+
+    Used to change the permission of file or folder
+
+        Symbol Meaning :
+
+        * a : For all (including owner, group and others)
+        * u : For owner
+        * g : For group
+        * o : For others
+        * r : read permission ( number 4 )
+        * w : write permission ( number 2 )
+        * x : execute permission ( number 1 )
+
+        Option :
+
+        * a+x : Add execute permission for all.
+        * a-x : Remove execute permission for all.
+        * 755 : rwx - user , r-x - group, r-x - others
+
+    How to use?
+
+        chmod a+x "file/folder name"
+        chmod 755 "file/folder name"
+
+-> echo :
+
+    To Print argument on the terminal
+
+        Option:
+
+        * -n : Not to add newline.
+        * ".." : String to print
+        * $PATH : variable ( environment variable, etc. )
+
+-> $PATH environment variable :
+
+    Store the paths which help in invoking executable, script, etc,
+    without specifying whole path, where its present.
+
+    How to add path to $PATH?
+
+    export PATH=$PATH:$(pwd)
+                        or full path to intended directory.
+
+-> SHABANG (#!/bin/bash)
+
+    Tells to use this interpreter to run the script.
+    Same as /bin/bash ./script
+
+-> Variables :
+
+    To stores data and can be changed.
+
+    1. Explicit Defination :
+        VAR=value
+        COUNT=5
+        PATH=/var/lib
+
+    2. Read command :
+        read VAR
+        read COUNT
+        read PATH
+
+        Option :
+
+        * -p :  to print the parameter before read.
+
+            How to use?
+
+                read -p "Your name: " NAME
+
+        * -s :  to hide the input to be taken. Best use
+                for password.
+
+            How to use?
+            
+                read -sp "Your age: " AGE
+
+    3. Command Substitution :
+
+        To store the output of the command executed to the variable.
+
+        How to use?
+
+            VAR=$(pwd) or VAR=`pwd`
+
+
+    How to use variables?
+
+        Use $variableName for using variables.
+
+
+-> For Math Calculation :
+
+    1 . let
+
+        let RESULT=NUMBER+5
+        let NUMBER++
+        let NUMBER--
+        let NUMBER+=5
+        let NUMBER-=5
+
+    2. (( ))
+
+        RESULT=$(( NUMBER + 5 ))
+    
+    3. []
+
+        RESULT=$[ NUMBER + 5 ]
+    
+    4. expr 
+
+        RESULT=$(expr $NUMBER + 5)
+        RESULT=`expr $NUMBER + 5`
+        RESULT=`expr 2 + 3`
+
+    5. bc ( used for floating point number )
+
+        RESULT=`echo "$NUMBER * 1.9" | bc`
+
+
+-> Argument :
+
+
+    $0 - script name
+    $1 - first argument
+    $2 - second argument
+    $n - nth argument
+    "$@" - all argument, expands as "$1" "$2" "$3"
+            and so on.
+    "$*" - all argument as string, "$1c$2c$3", 
+            where c is IFS (Internal field
+            separator), which is usally whitespace.
+    $# - arguments count
+
+-> Redirecting and piping:
+
+    Redirecting
+
+    * STDIN (0) - Standard input (data provided to program)
+    * STDOUT (1) - Standard output (what program prints, defaultly to the terminal)
+    * STDERR (2) - Standard error (what error message program prints, defaultly to terminal)
+
+    examples:
+    cat file1.txt > output_from_cat.txt
+    cat file1.txt 1>output_from_cat.txt
+    cat file1.txt 2>error.txt
+    cat file1.txt 1>output_from_cat.txt 2>error.txt
+    cat file1.txt &> output_from_cat.txt (from both 1 and 2)
+    cat file1.txt 1> output_from_cat.txt 2>&1(redirecting error to output)
+
+    cat file1.txt >> output_from_cat.txt(adding output instead of replacing it)
+
+    Piping
+
+    output of preceeding program is input to succeeding
+    program.
+
+    Program1 | Program2
+
+    examples:
+    cat file.txt | wc -l
+    cat file.txt | head -5 | tail -3 | wc -l
+
+-> Exit Status
+
+    echo $?
+
+    $? will give a return value of previous command.
+    It's the return value, called EXIT STATUS.
+    Successfully exiting give 0 value otherwise
+    non-zero value.
+
+    We can exit script using exit command.
+    exit command can be used with number 0 - 255.

arguments.sh

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+#!/bin/bash
+
+IFS=","
+echo "Script name: $0"
+echo "First argument: $1"
+echo "Second argument: $2"
+echo "All arguments with \$@: $@"
+echo "All arguments with \$*: $*"
+echo "Arguments count: $#"

configure.in

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 AC_INIT(["Name of Program"], [ Version X.X.X], ["author email"])
 
-AM_INIT_AUTOMAKE
+AM_INIT_AUTOMAKE()
 
 AC_CHECK_PROGS(CC,[clang, gcc, xlc, icc], [""])
 AC_PROG_CC

time_measurement.sh

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+#!/bin/bash
+
+#start time measurement from here
+START=$(date +%s)
+CURRENT_DIRECTORY=$(pwd)
+sleep 2 #sleep 2 seconds
+END=$(date +%s)
+
+#end time measurement
+DIFFERENCE=$(( END - START ))
+
+echo
+echo Time elapsed: $DIFFERENCE seconds.