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UNIX Scripting

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# 8  
Old 02-04-2014
I think the trouble is he's literally using cat $file without setting file. but there is no reason to cat and pipe a file. it's a useless use of cat. grep works on files.

Code:
grep -e ^Owner -e ^machine file

# 9  
Old 02-04-2014
make the grep case-insensitive by changing the command to
Code:
cat script.txt | egrep -i "^machine|^Owner

# 10  
Old 02-04-2014
Thanks a lot Macro!!!!It worksSmilie
# 11  
Old 02-04-2014
You can give awk a try:
Code:
awk '/^machine/||/^Owner/' file

BTW, this is useless use of cat
Code:
cat $file | egrep -i "^machine|^Owner"

This should be sufficient:
Code:
egrep -i "^machine|^Owner" $file

# 12  
Old 02-04-2014
Hi Vinoth, great.

for those calling things useless...... In my opinion using `cat` as an example is easy to understand, so useful. There are many one-liners (without useless things) which take hours to understand what is really happening. My scripts are easy to read, how 'bout yours??????
# 13  
Old 02-04-2014
Quote:
Originally Posted by ocrambo
Hi Vinoth, great.

for those calling things useless...... In my opinion using `cat` as an example is easy to understand, so useful. There are many one-liners (without useless things) which take hours to understand what is really happening. My scripts are easy to read, how 'bout yours??????
Useless use of cat is a waste of time, and it costs you an extra process.
# 14  
Old 02-04-2014
Quote:
Originally Posted by ocrambo
Hi Vinoth, great.

for those calling things useless...... In my opinion using `cat` as an example is easy to understand, so useful. There are many one-liners (without useless things) which take hours to understand what is really happening. My scripts are easy to read, how 'bout yours??????
Using:
Code:
cat file | grep expression

  • uses two processes,
  • causes the data in file to be read by cat, written by cat, and read again by grep, and
  • runs slower
than using:
Code:
grep expression file
    or
grep expression < file

both of which:
  1. use only one process,
  2. only reads the data in file once, and
  3. run faster.
That is why we call the first form a useless (and inefficient) use of cat.
With a little more experience, you will find either of the latter forms of these command lines just as easy to read as the first form.
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