[SOLVED] grep in pattern matching in a loop

francy_casa · 09-29-2011, 12:20 PM

Hi,

I am trying to go through a large file and check if some values exist using the 'grep' command, and I would like to output a file listing the values that exist.
This is what I have….but it does not work obviously…could you please help me figure out why?

Code:

#!/bin/bash
>matches.txt
for i in 'pattern.txt'
do
echo $i
$j='grep -c "$i" myfile.txt'
echo $j
if [$j -ne 0]
then
echo $i >> matches.txt
fi 
done

colucix · 09-29-2011, 12:32 PM

There are many errors in your script. First attempt?

Here is a working version:

Code:

#!/bin/bash
> matches.txt
for i in $(cat pattern.txt)
do
  echo $i
  j=$(grep -c "$i" file1)
  echo $j
  if [ $j -ne 0 ]
  then
    echo $i >> matches.txt
  fi
done

Basically you have to use command substitution to put the result of grep into the j variable: the syntax uses backticks ` (not single quotes as in your code) or even better:

Code:

$(command)

Then pay attention to the spaces inside the if/then expression: they are required to separate the square brackets from the expression. Check the differences with your version for other issues and feel free to ask if something is still not clear.

francy_casa · 09-29-2011, 12:46 PM

Thank you colucix!! Yes…it was my first attempt…I had no idea about the command substitution,
The script works great!
Just one more question to understand this further, out of technical curiosity…Is it easy to store in the output file also the results from $j's number of times the match is found? If this is complicated it does not matter (I would not understand this anyway so please don't waste your time…)

Thank you very much!

grail · 09-29-2011, 01:07 PM

Just include $j in the echo

francy_casa · 09-29-2011, 07:03 PM

yes of course…makes sense. Thank you!