help in grep

Shell Programming and Scripting
1

hi all,

could any one tell me what is diffrence in using " " and ' ' in grep.
eg what is diff in the following

 grep  "ram"    filename

  grep  'ram'     filename
2

You will not find any difference between those two grep's. Rather try these two and see the difference.

grep '$USER' /etc/passwd
grep "$USER" /etc/passwd

Open the man pages of sh or ksh and see the section on Quoting. Basically single quotes prevent variable expansion.

3

Adding to Vino's comment...
variables in single quotes are treated as const. string

as

  1. var = 5 ;
    echo '$var'

This will simply display the string $var as it is, no variable replacement by value.

  1. var = 5;
    echo "$var"
    In double quotes variables get expansion in terms of its value.
    o/p will be 5

Similarly is the case with grep '$var' and grep "$var".
But when it comes to constant string, it hardly reflects any change.

grep -w "string1 string2" file1
grep -w 'string1 string2" file1

Both are same.

Hope you get this !!:b: