How to concatenate rows of 2 files !

Trickie · 04-05-2011, 12:24 PM

@grail - OK, two errors: the first is mine for missing the trailing dots in "file 1", the second is yours for mis-reading the spec.

Richard

Telengard · 04-05-2011, 02:04 PM

Quote:

Originally Posted by grail

Your on

Very cool!

The only part I don't grok is this.

Code:

exec 3<file1 4<file2
...
exec 3<&- 4<&-

Is it truly necessary to call exec to acquire the desired FDs?
How can you safely assume FD 3 and FD 4 are free for use in any particular environment?

chrism01 · 04-05-2011, 07:10 PM

Like FDs 0 (stdin), 1 (stdout), 2 (stderr), more FDs are avail at each shell invocation. It is hoped you know what your current prog/script has used/is using at any time.

Analogous to params $0, $1, $2 etc ...

grail · 04-06-2011, 03:28 AM

Quote:

Is it truly necessary to call exec to acquire the desired FDs?

Happy to see an alternative. I will admit that I am at less than a year of experience with them so still learning.

Quote:

How can you safely assume FD 3 and FD 4 are free for use in any particular environment?

I guess you could make it more robust to check prior to running and use the first available ones, but:

1. Was only really looking at a simple solution
2. As with first answer, happy to know more ways to identify those in use and how to choose next ones

Telengard · 04-06-2011, 10:11 AM

Quote:

Originally Posted by grail

happy to know more ways to identify those in use and how to choose next ones

Here's what I found.

Quote:

Originally Posted by Bash Reference Manual -> 3.6 Redirections

Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally.

http://www.gnu.org/software/bash/man...l#Redirections