Re: FWD: About Bash Script

[Mart Frauenlob]

On 16.02.2010 19:52, Curtis wrote:
> Thanks pk!
> 
> That's the same thin Greg told me.
> 
> #!/bin/bash
> 
> 
> if [! -e b.txt];

if [[ ! -e b.txt ]; then ...; fi

or

if [[ ! - b.txt ]]
then
...
fi

you only need the semicolon if you omit the newline.

> 
> then
> 
> mv a.txt b.txt
> 
> exit
> 
> fi
> 
> 
> 
> #The previous commands checks to see if b.txt is NOT already there, if
> NOT, it renames a.txt to b.txt
> 
> 
> 
> #If the script gets here, b.txt EXISTS..........
> 
> # does_exist is a recursive function....looking at b.txt(i) ......the
> first b.txt(some number) it finds NOT existing...it creates....
> 
> 
> 
> set i = 1

set??? see: help set

i=1
or
declare i=1

see: help declare (in you bash prompt)

> 
> does_exist[]

you want to define a function?

does_exist() {

<code_here>
}

> 
> 
> 
> if [-e b.txt.$i];
> {

this `{' one is bad here.

> 
> then
> 
> i = i +1

i=$((i + 1))
or
i=$((i++))
or
let i++
or
let i+=1

> 
> does_exist
> 
> else
> 
> mv a.txt b.txt.$i
> exit
> fi
> }
> 
> 
> I'm close but getting an eror near the last line....not really sure
> why....
> ./test: line 25: syntax error near unexpected token `fi'
> ./test: line 25: `fi'
> 

May i suggest some readings:

http://tldp.org/LDP/abs/html/index.html
http://bash-hackers.org/wiki/doku.php/start
http://mywiki.wooledge.org/BashFAQ
http://tiswww.case.edu/php/chet/bash/FAQ

I sent you this link in my first reply to you:
http://groups.google.com/group/comp.unix.shell/browse_thread/thread/233d175274e246bd/b4deba6bf5fea99a?lnk=raot

This thread talks about race conditions, that is what i based my first
piece of code for you on. That's why i tried not to use
if condition then react - type of stuff.
Might not affect you at all.

However, we see what you are trying to do, but we don't know what for.
I guessed file downloading, greg guessed log rotating.
It might be a good idea to provide some more information, because that
might lead to different solutions.

Again however, as i didn't do that before myself, i tried to write some
what hopefully meets your requirements:

#!/bin/bash

f() {
[[ $2 ]] || return 1
set -f
set -C
local in_file="$1" out_file="$2"
local i=0 ext=
(
    until command exec 3> "$out_file$ext"; do
        ext=.$((i++))
    done
    exec cat "$in_file" >&3
) 2>/dev/null || exit 1
}

f /tmp/a /tmp/b || echo "error"

---
the function takes 2 parameters, the name of the input file and the name
of the file which may already exist.
read the above link, it explains like all commands used here.

Best regards

Mart