for sed elif

#!/bin/bash
for i in a b c
do
echo $i
done

bash for1 

a

b

c

-----------

GNU sed has the option -i to update the file

sed s/for/sss/g for1 -i

ubuntu2@ubuntu2:~/Documents/shellscripting$ cat for1

#!/bin/bash

sss i in a b c

do

echo $i

done
---------
How to add text to the particular line in the file:
 sed -i '1s/^/task goes here\n/' for1

------------
sed -n '1p;$p' file.txt will print 1st and last line of file.txt .
----------
 cat for1
#!/bin/bash
for i in a b c
do
echo $i
done
if [ "$?" -ne "0" ]; then
echo not ok
else
echo ok
fi

bash for1

a

b

c

ok

-----------
cat ifelif1
#!/bin/bash    
#   elif example
##################
echo Hi
OS=`uname -s`
if [ "$OS" = "Linux" ]; then
echo Linux
elif [ "$OS" = "UNIX" ]; then
echo UNIX
fi

bash ifelif1 

Hi

Linux

-------------
cat whileread
#/bin/bash
while read -p "Enter file name: " filename
do
if [ ! -e "$filename" ]; then
echo File doesnt exist
continue
fi
if [ -f "$filename" ]; then
echo Regular file
elif [ -d $filename ]; then
echo Directory
fi
done

bash whileread 

Enter file name: t

Directory

Enter file name: for1

Regular file

--------------