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Full Discussion: Piping commands
Top Forums UNIX for Dummies Questions & Answers Piping commands Post 302786735 by iliya24 on Thursday 28th of March 2013 06:13:22 AM
Old 03-28-2013
Quote:
Originally Posted by rbatte1
This is known as a useless use of cat

There is no point running the cat command. It costs you a process and it's much neater to write:-

Code:
grep '^[A-Da-f]' f1 >> f2

This will get all lines starting with (the carat ^) uppercase A, B, C or D ; or lower case a, b, c, d, e or f from file f1 and append them to file f2

is this what you wanted to do?



Robin

---------- Post updated at 10:06 AM ---------- Previous update was at 10:00 AM ----------

Ah! An extra reply whilst I was typing.

The difference in the expressions '^[A-Da-f]' & '[^A-Da-f]' are subtle in the text but very different in meaning:-
  • '^[A-Da-f]' means that the string starts with one of the characters in the range in square brackets.
  • '[^A-Da-f]' means that the expression is to exclude all the characters in the range.

If you use the form with the carat ^ inside the square brackets, then you are saying get me all records that do not contain any of A, B, C, D, a, b, c, d, e or f.


Is that clearer?


Robin
Thx
No i saw this command in a queze question was what dose it do?
So basically i am not trying to do some thing i just trying to understand.
Could u explain me what the meaning of ^???
difference between if it inside brakets or outside?
Thx

---------- Post updated at 05:10 AM ---------- Previous update was at 05:09 AM ----------

Quote:
Originally Posted by rbatte1
This is known as a useless use of cat

There is no point running the cat command. It costs you a process and it's much neater to write:-

Code:
grep '^[A-Da-f]' f1 >> f2

This will get all lines starting with (the carat ^) uppercase A, B, C or D ; or lower case a, b, c, d, e or f from file f1 and append them to file f2

is this what you wanted to do?



Robin

---------- Post updated at 10:06 AM ---------- Previous update was at 10:00 AM ----------

Ah! An extra reply whilst I was typing.

The difference in the expressions '^[A-Da-f]' & '[^A-Da-f]' are subtle in the text but very different in meaning:-
  • '^[A-Da-f]' means that the string starts with one of the characters in the range in square brackets.
  • '[^A-Da-f]' means that the expression is to exclude all the characters in the range.

If you use the form with the carat ^ inside the square brackets, then you are saying get me all records that do not contain any of A, B, C, D, a, b, c, d, e or f.


Is that clearer?


Robin
Thx i posted a replay before seeng your explanation very good thanks!!!

---------- Post updated at 05:13 AM ---------- Previous update was at 05:10 AM ----------

Ok i am getting it but what means this ' [A-Da-f]' without the ^ sign?
Thx.
 

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