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output redirection in scripts

 
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# 1  
Old 02-28-2009
output redirection in scripts
I am trying to write a script that will remove any line in 2 given text files
starting with '-'.
the output should be to the second file.
this is what I tried:
Code:
#!/bin/csh -f
cat $1 $2 | grep -v '^-' > $2

the problem is the after executing the script, file2 contains only the
lines from file1.
for example:
before:
file1:
A
B
-C

file2:
D
E
-F

after:
file 2:
A
B

can I do it without temp files?
# 2  
Old 02-28-2009
Because you can't have same input and output with grep.
# 3  
Old 02-28-2009
ok, so is there anyway to do it without temporary file?
# 4  
Old 02-28-2009
You can use this if it's ok to touch $1.
Code:
cat $2 >> $1; grep -v '^-' $1 > $2

This one doesn't touch $1 but the output is inverted ($2 then $1)
Code:
cat $1 >> $2; sed -i '/^-/d' $2

Last edited by chebarbudo; 02-28-2009 at 01:52 PM.. Reason: new idea
# 5  
Old 02-28-2009
well, I can't change file1 and the order should be file1 and then file2
# 6  
Old 02-28-2009
With some shells (bash and zsh) you can use something like this:

Code:
{ rm file2 && grep -v '^-' > file2;}< <(cat file1 file2)

# 7  
Old 02-28-2009
ok this worked:
Code:
grep -v '^-' > $1 << here
`cat $1 $2`
here

thanks a lot!
 
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