Convert Rows into Columns.

xargs -n1 < text_file.txt
or  
tr -s '[:blank:]' '\n' < text_file3.txt
or
tr -s ' '  '\n'< text_file3.txt > text_file4.txt
or
fmt -1 text_file3.txt

Reverse sorting.
sort -n -r numbers.txt

Writes results to file specified. sort -n -r numbers.txt -o sort_output.txt

Ignore case while sorting [option -f]
sort -f string.txt

Sort and remove duplicates [option -u].
sort -u string.txt

Numeric Sorting.

sort -n string.txt

Sorting according Specific Column [-k] with filed seprator[-t]*

sort -t ":" -k 3 -n /etc/passwd -n -> number sorting

Sort File/folder size

du -s ~/Learning/* |sort -nr

file Overwrite file with stdout

file append stdout to file 2> file Overwrite file with stderr 2>> file append stderr to file &> file Overwrite file with stdout and stderr combined &>> file append stdout and stderr to file

cat text_file1.txt \ text_file2.txt | grep Endorphins

The pipe connects the output of the first with the input of the second command. More details on this later.

Special Variables:

Sr.No. Variable & Description 1 $0 The filename of the current script. 2 $n These variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on). 3 $# The number of arguments supplied to a script. 4 $* All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2. 5 $@ All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2. 6 $? The exit status of the last command executed. 7 $$ The process number of the current shell. For shell scripts, this is the process ID under which they are executing. 8 $! The process number of the last background command.

#!/bin/sh

echo "File Name: $0"
echo "First Parameter : $1"
echo "Second Parameter : $2"
echo "Quoted Values: $@"
echo "Quoted Values: $*"
echo "Total Number of Parameters : $#"

1. Reading the user input and storing it in a variable

#!/bin/bash 
echo "What's your name?" 
read entered_name 
echo -e "\nWelcome " $entered_name

2. Reading from a file

while read line
do
  echo $line
done < input.txt

while read inpt
do
ping -c 3 $inpt
if [ $? = 0 ]
then
echo "The server $inpt is pinging"
else
echo "Unable to ping server $inpt"
fi
done < server.txt

3. Redirecting output:

ls > files.txt

This lists the files in the current directory and writes the output to a file named files.txt.

Conditional statements

Syntax:

if [[ condition ]];
then
    statement
elif [[ condition ]]; then
    statement 
else
    do this by default
fi

We can use logical operators such as AND -a and OR -o to make comparisons that have more significance.

if [ $a -gt 60 -a $b -lt 100 ]

Example 1:

#!/bin/bash
echo "\Please enter the number"
read num
if [ $num -gt 0 ]
then
  echo "The $num is positive number"

elif [ $num -lt 0 ]
then  
    echo "the $num is negative number"

else
  echo "Please enter valid number "
 
fi