[SOLVED] call awk from bash script behaves differently to awk from CLI = missing newlines

titanium_geek · 05-26-2011, 12:57 AM

So, (yes this is tangentially related homework, but I think this question is legal, because it isn't directly related to the assignment.)

I have a file, I want to append the 5th fields (aka 5th column) of that file into another file:

from the CLI:

Code:

awk '{print $5}' fileone >> file2 
cat file2

output:
word
word
word
(yes, this is what I want.)

so, I put that line in a bash file

Code:

awk '{print $5}' fileone >> file2
echo `cat file2`

this will output
word word word
(this is not what I want)

why is this doing this?

Code:

me $ bash --version
GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

The code has to run on these machines, so is there a work around to inserting a newline after each word?

Telengard · 05-26-2011, 01:35 AM

What's the point of echo `cat file2`? Don't you think cat file2 would be good enough?

I think what may be happening is that the transition from STDOUT of cat to argument of echo causes the field separator to be munged.

/me tests

Yeah, that's definitely it. Try it on the command line and see what happens.

Code:

foo$ cat infile
ab
a b
a  b
a--b
a   b
a    b
aaabbb
foo$ echo `cat infile`
ab a b a b a--b a b a b aaabbb
foo$

titanium_geek · 05-26-2011, 02:36 AM

EDIT. Didn't work.
EDIT EDIT: this is because, as I was trying to work out what was going wrong, I make awk printf rather than print.

heh. *me slaps head*

Thanks!

I think I got into my head that echo = C's printf. (tsk tsk)

TG

Telengard · 05-26-2011, 03:30 PM

Quote:

Originally Posted by titanium_geek

I think I got into my head that echo = C's printf. (tsk tsk)

Nope. Bash has its own printf, if you need formatted output.

But that is not what I mean. Here's what you were doing:

Code:

echo `cat file2`

It is pointless to pass STDOUT from cat as an argument list to echo, which then sends it to STDOUT. That is what is changing your newlines into blanks.

All you really need to do what I think you want is:

Code:

cat file2

No need for echo, no need for command substitution. Either way the contents of file2 are sent to STDOUT.

My recommendation is to eliminate the bug you described by eliminating the unneeded echo and command substitution.

titanium_geek · 05-26-2011, 09:06 PM

Thanks Telengard, I did remove the superfluous echos, wondered why it didn't work, then realised I needed to undo some of the poking I'd done to try and fix it before I found out that the echo was the problem.

TG