CODEWITHSUNDEEP
bashfileloopsgrep
stevo
stevo

Reputation: 181

bash execute multiple greps on each line in a file

I want to run 2 different greps sequentially on each line in a file so that it will output the matches in the order that occurred in the input file. I have a simple file called temp.txt that I will use for this example. Contents of this file are:

$ cat temp.txt
line1 a
line2 b
line3 c

I have the following code which I have simplified by using an echo instead of the first grep. 

#! /bin/bash

cat temp.txt | while read line
do
  echo $line
  grep b $line
done

I thought the output would have been:

line1 a
line2 b
line2 b
line2 c

But I am getting the following output:

$ ./debug.sh
line1 a
grep: line1: No such file or directory
grep: a: No such file or directory
line2 b
grep: line2: No such file or directory
grep: b: No such file or directory
line3 c
grep: line3: No such file or directory
grep: c: No such file or directory

Upvotes: 1

Views: 166

Answers (3)

twalberg
twalberg

Reputation: 62439

Perhaps you should only run one grep, but give it both patterns to look for:

grep 'pattern1\|pattern2' file.txt

Upvotes: 2

damienfrancois
damienfrancois

Reputation: 59250

Your script should look like this

#! /bin/bash

cat temp.txt | while read line
do
  echo $line
  grep b <<< "$line"
done

to get the output you want. grep is expecting input from a file or from stdin. Your syntax makes grep think it has to open a file. This version makes sure the $line is fed to its stdin.

Upvotes: 0

fedorqui
fedorqui

Reputation: 290025

You have to do something like:

#! /bin/bash

while read line
do
  echo "$line" | grep "b"
done < temp.txt

Or instead of echo "$line" | grep "b" you can also use:

grep "b" <<< "$line"

In your case,

grep b $line

was trying to grep b on a file called $line, which obviously does not exist.

Note there is no need to cat the file and pipe to the while: while read ... done < file makes it.

Upvotes: 1

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