Re: regex question

[Jim Cheetham]

ls | grep -v "\.dat$" | cat > newfile
but cat just gives me the list of files again. Any way to force cat to 
consider the lines as
The output from ls is just a list of filenames, so that's all that can 
appear at the far end of the pipeline here.

What you need to be doing is to use a 'for' loop, which allows you to 
step through the list of filenames one at a time, and do some action 
with them.

The command style is :-

for <variablename> in list of names
do
        action using <variablename>
done
Anything that the shell can use to generate a list of names is 
acceptable on the 'for' line, you could try ...

for i in 1 2 3 4 5 6 7 8 9 10
do
        echo $i
done
or, to expensively simulate ls
for i in *
do
        ls $i
done
If the list of names that you want to use comes as the output of a 
chain of other commands, you can use the subshell quoting of $(command) 
- this is equivalent but better than the old traditional backticks 
`command` that you might see around.

So, if ' ls | grep -v "\.dat$"' fives you the list of file you need ...

for i in $(ls | grep -v "\.dat$")
do
        ls -l $i
done
That will just list out the files with ls -l, I know that's not what 
you want just yet!

Now, you want to concatenate the contents of all the non-.dat files 
into one new file, yes? There's a couple of things to consider. If the 
output file you want to create is supposed to be in the same directory 
as all the others, either it must end with .dat, or it must not exist 
when you do your initial ls - otherwise your command will include the 
output file in it's own input, which would be confusing to say the 
least!

And, you have to be careful with the redirection operator ">" that you 
used earlier. That does a create/overwrite on the target file - if you 
ran it 10 times, only the last output would be found in the file. You 
need to use the ">>" operator - create/append.

So, your command starts to look like this -

rm outputfile
for i in $(ls|grep -v '\.dat$')
do
        cat $i >> outputfile
done
-jim