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Old 04-14-2013, 05:44 AM   #1
woodyhead
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Talking Shell Script Help


I'm new to shell scripting and I want to be able to print the lines in between the head and tail of a .txt file.

for example, if I wrote on the command line: ./scriptname filename 4 10
would print lines 5 6 7 8 9 10?


cheers!
 
Old 04-14-2013, 06:03 AM   #2
druuna
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What have you tried this far and where are you struggling with?
 
Old 04-14-2013, 06:07 AM   #3
woodyhead
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So far I am able to print the head and the tail, the problem is when it comes to printing the lines inbetween and the head and tail..

my code so far...
#!/bin/bash

echo "Printing head of $1"
head $1

echo "Printing tail of $1"
tail $1

thank you!
 
Old 04-14-2013, 06:10 AM   #4
druuna
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You should have a look at the sed command, which can print ranges.

Sed resources:
 
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Old 04-14-2013, 08:15 AM   #5
vineethsp
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Quote:
Originally Posted by woodyhead View Post
I'm new to shell scripting and I want to be able to print the lines in between the head and tail of a .txt file.

for example, if I wrote on the command line: ./scriptname filename 4 10
would print lines 5 6 7 8 9 10?


cheers!
try taking head first.... nd then tail..

for example the inputs given by you were 4 and 10, so you can give

Quote:
head 10
tail (10-4)
i don't know for the syntax errors but a kind of sudo code would look like

Quote:
a=[arguement 2]
b=[arguement 2] - [arguement 1]
cat [filename] | head a | tail b
you can google for proper syntax.....
 
Old 04-14-2013, 09:11 AM   #6
woodyhead
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Thats a great help thank you vineethsp !
However as I am a newbie Im still stuck with the proper syntax for it!
I know to pass the parameters are $0 $1 $2 ... etc.(http://www.dreamsyssoft.com/unix-she...s-tutorial.php)

Can't think how a and b would work though? agh

Thanks
 
Old 04-14-2013, 09:25 AM   #7
druuna
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Code:
#!/bin/bash

FILE="$1"
START="$2"
END="$3"

sed -n "${START},${END}p" ${FILE}

exit 0
 
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Old 04-14-2013, 09:29 AM   #8
jpollard
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How about something simple...
Code:
count= $(wc -l file)
tail $((start - count)) | head $((count - start - end))
But I like the sed approach better.

Last edited by jpollard; 04-14-2013 at 09:30 AM.
 
Old 04-14-2013, 09:51 AM   #9
vineethsp
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Quote:
Originally Posted by woodyhead View Post
Thats a great help thank you vineethsp !
However as I am a newbie Im still stuck with the proper syntax for it!
I know to pass the parameters are $0 $1 $2 ... etc.(http://www.dreamsyssoft.com/unix-she...s-tutorial.php)

Can't think how a and b would work though? agh

Thanks
you can use the values in variable as

Quote:
file=$1
a=$3
b=`expr $3 - $2`
cat $file| head $a | tail $b
Hope this helps you \m/
 
Old 04-14-2013, 10:46 AM   #10
woodyhead
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I'm getting there slowly haha!

I am getting a error message when I run the script

"expr: non-numeric argument" and I used 2 and 3 to run it, it said "2: no such file or dierectory"

thanks
 
Old 04-14-2013, 12:05 PM   #11
David the H.
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If you're getting errors, show us the exact code you ran that produced it. We can't tell you what you're doing wrong if we can't see what you did.

And please use ***[code][/code]*** tags around your code and data, to preserve the original formatting and to improve readability. Do not use quote tags, bolding, colors, "start/end" lines, or other creative techniques.


In any case, however, don't use expr. Forget that it even exists. It's completely superfluous in all modern shells, which have features built-in that can do everything that old fossil can do and more.

http://mywiki.wooledge.org/BashGuide..._Ever_Do_These

Use bash's arithmetic evaluation, string manipulation, and testing features instead.
 
Old 04-14-2013, 12:12 PM   #12
woodyhead
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sorry about the formatting, I hope I've done it right now...

***
Code:
#!/bin/bash
#script name

filename=$0
a=$2
b=`$2 - $1`
cat $filename | head $a | tail $b
***

cheers!
 
Old 04-14-2013, 12:25 PM   #13
David the H.
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But how are you running the script? What do the values $0, $1, and $2 hold?

I don't think you realize that $0 stores the name of the script, according to how it was launched. It's very rare that you should actually need to use that parameter. $1 holds the first argument to the script.

PS:

1) Useless Use Of Cat.

2) The syntax of head and tail use "-n" to specify their line numbers.

3) QUOTE ALL OF YOUR VARIABLE EXPANSIONS. You should never leave the quotes off a parameter expansion unless you explicitly want the resulting string to be word-split by the shell and any possible globbing patterns expanded. This is a vitally important concept in scripting, so train yourself to do it correctly now. You can learn about the exceptions when you need them.

http://mywiki.wooledge.org/Arguments
http://mywiki.wooledge.org/WordSplitting
http://mywiki.wooledge.org/Quotes

Code:
#!/bin/bash

filename=$1
a=$3
b=$(( $3 - $2 ))

head -n "$a" "$filename" | tail -n "$b"

exit 0

Last edited by David the H.; 04-14-2013 at 12:31 PM. Reason: moar
 
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Old 04-14-2013, 12:29 PM   #14
woodyhead
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When I run the script in command line I want to be able to run it by:

Code:
./scriptname.sh filename 3(head) 5(tail)
so it prints the lines in between the two numbers?

thanks!
 
Old 04-14-2013, 01:14 PM   #15
David the H.
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Yeah? Well, as explained, $1 will be the filename, $2 the "head" number, and $3 the "tail" number. Now it's up to you to figure out how to use them properly.

By the way, I didn't actually test the code above before I posted it. I don't think it gives you exactly what you want. You'll have to modify the math and code flow to get it to output the proper lines. Or use different a different tool, as has also been shown to you.

In any case we've given you all the resources you need to do what you want, so get on it! Post back what you come up with.

Last edited by David the H.; 04-14-2013 at 01:16 PM. Reason: fixes
 
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