Question

I have a text file named “file1” containing the following data :

apple  
appLe  
app^e  
app\^e  

Now the commands given are :

1.)grep app[\^lL]e file1  
2.)grep "app[\^lL]e" file1  
3.)grep "app[l\^L]e" file1  
4.)grep app[l\^L]e file1

output in 1st case : app^e

output in 2nd case :   
                     apple  
                     appLe  
                     app^e  

output in 3rd case :  
                     apple  
                     appLe  
                     app^e

output in 4th case :  
                     apple  
                     appLe  
                     app^e  

why so..?
Please help..!

Answer 1

 1.)grep app[\^lL]e file1

The escape (\) is removed by the shell before grep sees it so this is equivalent to app[^lL]e. The bit in brackets matches anything not (from the ^, since it’s the first character) L or l

 2.)grep "app[\^lL]e" file1

This time, the \ escapes the ^ so it matches ^ or L or l

 3.)grep "app[l\^L]e" file1

^ works to negate the set only if it is the first character, so this matches ^ or L or l

  4.)grep app[l\^L]e file1

The ^ is escaped, but since it’s not the first it doesn’t make any difference, so it matches ^ or L or l