Shell Programming and Scripting

Hi I am trying to write a bash script to add a line of text to the middle of a file.

The way I worked it out was to calculate the number of lines and divide by 2. The file I am using is called newfile and it just contains lines of data.

The new file I have created I have called midfile and the line of text which will be added is called myline.

code I have done so far is below:

Code:

#!/bin/bash
 
num=$(((wc -l $newfile)/2))
 
cat newfile | head -$num > midfile
cat myline >> midfile
cat newfile | tail -$num >> midfile

At the moment the new file is created but it only contains the line which is supposed to go in the middle. Im guessing the mistake I have made is simple but can't seem to figure out where I have gone wrong. Many Thanks in Advance.

check the output/error of this command. I think you will get syntex error.

try this:

Code:

num=$(expr $(wc -l < $newfile) / 2)

Try:

Code:

num=$(($(wc -l<newfile)/2))

Thanks Scrutinizer.....that is working great.....can u briefly explain why you add a < so i can understand......am a new starter

Hi, if you use < then the wc command leaves out the file name.

you can check by own.

Code:

/home->wc -l file
11 file
/home->wc -l < file
11
/home->

"<" is the indirection, which is sending file o/p to the command line by line.
as a result of that, you will get the line count only. ( unlikely the filename also which you get in the another command.)

if you use first command than you will have to suppress the filename part.

Thanks, I tried that and it makes sense now.....

Was thinking....would separating the filename in brackets allow you to not include the filename??