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read from file and grep using shell

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# 1  
Old 02-14-2012
read from file and grep using shell
Hi Guys,

I have a small script which greps for the username reading from stdinput.

./file.sh pattern

Code:
pattern=$1
grep "blah blah.*$pattern" /home/user/log.txt

Instead of typing the pattern everytime i want to read the pattern from a file inside the shell script and execute the grep command for each pattern. Please advise if this can be done.

Cheers
# 2  
Old 02-14-2012
Code:
while read -r pattern; do
...
done

Redirect the read or while loop to your file (either within the script or upon invocation).

Depending on what you are trying to accomplish, you might even be able to just use grep's -f option, which reads patterns from the file provided.

Regards,
Alister
# 3  
Old 02-14-2012
Hi Alister,

Cheers for the reply mate. I'm a newb at this..so i'm assuming the syntax would be as follows:

Code:
pattern<<file.txt
while read -r pattern; do
grep "blah blah.*$pattern" /home/user/log.txt

# 4  
Old 02-15-2012
MySQL
you can try with below script too.

Code:
#! /bin/bash

while read pattern
do
grep "blah blah.*$pattern" /home/user/log.txt
done <file.txt # text file containing pattern

# 5  
Old 02-15-2012
Or
Code:
sed 's/^/blah blah.*/' patternfile | grep -f- /home/user/log.txt

# 6  
Old 02-15-2012
Quote:
Originally Posted by kalpeer
you can try with below script too.

Code:
#! /bin/bash

while read pattern
do
grep "blah blah.*$pattern" /home/user/log.txt
done <file.txt # text file containing pattern

Unless backslashes are to be treated as special characters, you really want to use read's -r option. Given that regular expressions are more likely to contain backslashes than standard text, -r is particularly important when handling them.

Regards,
Alister
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