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Old 11-17-2004, 04:34 PM   #1
alts
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Getting info from text file


Warning, REAL newb here!

I have a script that, as of now, reads in a .txt file, takes all the lines (all the lines are 8 characters long always), writes and chmods a new, blank, .txt file with the same name and passes this info on to another script. It works perfectly.

I now want to alter this script so that it takes only the first line of the .txt file, deletes that line from the file, writes the file back (minus that one line of course) and passes that one line on to my other script.

I am doing this so multiple computers can access and process the lines in order without affecting the rest of the lines in the .txt file and without processing any line multiple times. Please excuse the dirty(?) coding of the script . . . I am brand new:

(The "sUpdate.que" is the said .txt file used)

while read shotIn; do
shots[${#shots[@]}]=$shotIn

rm /Volumes/Projects01/ShellScripts/sUpdate.que
touch /Volumes/Projects01/ShellScripts/sUpdate.que
chmod 777 /Volumes/Projects01/ShellScripts/sUpdate.que
done < /Volumes/Projects01/ShellScripts/sUpdate.que

for shot in "${shots[@]}" ; do

echo $shot

/Volumes/Projects01/ShellScripts/shakeRender $shot
echo `date` "$shot" >> /Volumes/Projects01/ShellScripts/sUpdate.log
done


Thanks for any help!
alts
 
Old 11-17-2004, 05:10 PM   #2
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Moved: This thread is more suitable in "Programming", and has been moved accordingly to help your thread/question get the exposure it deserves.
 
Old 11-17-2004, 08:00 PM   #3
sirclif
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well, i dont know the language your using very well, im assuming bash. but a quick fix would be to just keep track of what line your reading and writing by having some index variable start at zero and increase everytime you read a line. then you can check with an if statment to see if you need to write that line.

i = 1
while shot in; do
{
if($i != 1)
{ write to your file}
$i++
}

sorry for the poor syntax, im not sure what it will look like, but you get the idea
 
Old 11-17-2004, 08:09 PM   #4
alts
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It is bash, sorry for not stating earlier.

Thanks for the reply. Because the amount of lines in this file may vary greatly, isn't it easier, and cleaner, to just remove the the line and always have script read line 1? Otherwise the script has to check what lines have been read and find the next one that has not been read. With the method I am thinking of, it's also easier to spot where problematic lines are as they will be at the top of the file if the script fails. Again, I could be wrong about the best way to go about this but that's why I am here. I've been pouring over books and I just can't get the syntax right. I'll buy beers if someone can help me! Thanks again!

alts
 
Old 11-18-2004, 08:49 AM   #5
sirclif
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oh, im sorry, i misunderstood your problem. you want the script to just take the first line of the text file, and remove that line so that if another script opens the file, it wont have to worry about weather or not that line has been processed. is that about it? your right, my solution is not very efficient for that.

well, you could easily read the first line of the file into an variable using the head command.

VARIABLE = `head -n 1 filename.txt`

but im not sure how to just remove the first line without actually reading and writing each line in the file. ill think about it
 
Old 11-18-2004, 09:12 AM   #6
ahh
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You can use
Code:
tail -n +2 file.txt > temp.txt; mv temp.txt file.txt;
to replace the file with one that has the first line removed.
 
Old 11-18-2004, 09:34 AM   #7
sirclif
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of course, good idea
 
Old 11-18-2004, 11:06 AM   #8
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Quote:
Originally posted by sirclif
oh, im sorry, i misunderstood your problem. you want the script to just take the first line of the text file, and remove that line so that if another script opens the file, it wont have to worry about weather or not that line has been processed. is that about it? your right, my solution is not very efficient for that.

well, you could easily read the first line of the file into an variable using the head command.

VARIABLE = `head -n 1 filename.txt`

but im not sure how to just remove the first line without actually reading and writing each line in the file. ill think about it
sed -i '1d' filename.txt
That will remove the first line in-place (if your sed is version 3.x)

Btw - in this context it's whether, not weather ;)


Cheers,
Tink
 
Old 11-18-2004, 11:17 AM   #9
sirclif
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yes, sorry about that. I just think of the word and my fingers decide how to spell it
 
Old 11-18-2004, 11:44 AM   #10
alts
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Thanks for all the help. This is exactly what I was looking to do! One question though 'ahh' - I need to flag the 'tail' command to write back ALL lines other than the one we removed and the amount of lines could vary significantly (say 5 -200). Maybe I am not quite understandign the 'tail' flags yet but does the way you've written it only write back two lines?

Thanks again for the help.
 
Old 11-18-2004, 11:49 AM   #11
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sirclif's signature

If you don't care how it's spellt maybe
you should stick to talking ;)


Cheers,
Tink
 
Old 11-18-2004, 12:04 PM   #12
ahh
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If you use the format
Code:
tail -n +x
where x is a number, it will read the entire file starting from the line x lines from the start of the file.

May I suggest
Code:
man tail
or
Code:
info tail
if you are interested in the various ways tail can be used?
 
Old 11-18-2004, 01:26 PM   #13
alts
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Sorry to bother you guys again. In the declaration of the variable to get line 1 from my text file:

line1='head -n 1 /path/path/filename.txt'

I am getting an error that during "read $line1" command tha:
" '-n': not a valid identifier "

What am I doing wrong?
 
Old 11-18-2004, 03:06 PM   #14
alts
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I got it working perfectly! I cannot thank all of you enough for your help. Like I said, I'm buying beers (when you come to the States)!

Cheers,
alts
 
Old 11-18-2004, 03:20 PM   #15
alts
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. . . well, almost . . .

One more thing I need is this script to query the text file to see if there's anything in it and then run once again if there is, in fact, any more info in the text file.

I know this will be using a "while" loop but again I am stuck on the proper syntax . . .
 
  


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