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Shell Script Linux

the first line in the shell script should be the interpreter location to be used

#!/bin/bash ----> this interpreter is taken to execute the file

if this is not there the shell which launched this will be taken.

 

echo –n no new line

eco –e take special

Double Quotes does interpolation , substitutes with var value
Single Quotes no manipulation directly prints
Back Quotes executes a command and gives us output.

Special variables in shell

program to print

  • program name
  • number of paramerters
  • all arguments

echo "program name is $0"
echo "argument one dollar 1 $1"
echo "argument two dollar two $2"
echo "argument three Dollar three $3"
IFS=":"
echo "all args $@ "
echo "all args with delimiter $* "

 

If in Shell Script:

if test $x –lt $y

OR

if [$x –lt $y]

Check the file properties

root@v11> if [ -e shell.sh ]; then echo yes ; else echo no; fi
yes
root@v11> if [ -f shell.sh ]; then echo yes ; else echo no; fi
yes
root@v11> if [ -d shell.sh ]; then echo yes ; else echo no; fi
no
root@v11> if [ -L shell.sh ]; then echo yes ; else echo no; fi
no
root@v11> if [ -r shell.sh ]; then echo yes ; else echo no; fi
yes

Case in Shell Script:

case $1 in
  a) echo "this is a";;
  b) echo "this is b";;
  c) echo "this is c";;
  *) echo "this is default";;
esac

While in Shell Script:

num=0;
while [ $num -lt $# ]
do
echo $num
      num=$[num+1]
done

Until in Shell Script:

For in Shell Script:to print all the command line arguments passed using for

for i in $@
do
  echo $i
done

 

Handling Signals

trap "echo trapped; exit;" SIGINT

while [ 1 ]
do
echo "hi"
done

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