Using Grep In A For Loop

Question

/home/errorcodes contains:

421 RP-001
421 RP-002
421 RP-003
550 SC-001
550 SC-002
550 SC-003
550 SC-004
550 DY-001
550 DY-002
550 DY-001
550 OU-001
550 OU-002

Script:

#!/bin/bash

Elogs=/home/elogs.txt
Errors=/home/errorcodes
for i in `cat $Errors`; do
    #Get Error Logs
    grep "$i" /home/eximlog >> $Elogs
done

Debug:

+ cat /home/errorcodes
+ for i in '`cat $Errors`'
+ grep 421 /home/eximlog
+ for i in '`cat $Errors`'
+ grep RP-001 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 421 /home/eximlog
+ for i in '`cat $Errors`'
+ grep RP-002 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 421 /home/eximlog
+ for i in '`cat $Errors`'
+ grep RP-003 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep SC-001 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep SC-002 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep SC-003 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep SC-004 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep DY-001 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep DY-002 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep DY-001 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep OU-001 /home/eximlog
+ for i in '`cat $Errors`'
+ grep 550 /home/eximlog
+ for i in '`cat $Errors`'
+ grep OU-002 /home/eximlog

Why does the loop read all codes like "421" and "RP-001" separately? And bring duplicate result. Grep should consider codes a single string like: "421 RP-001" And debugging should be like this:

+ for i in 'cat $Errors'
+ grep 421 RP-001 /home/eximlog
    ︙

John1024 · Accepted Answer · 2016-06-08 06:38:36Z

7

The shell will perform word splitting on $(cat $Errors). That is why you get one word at a time instead of one line at a time.

You want a while read... loop:

while read -r line; do
    #Get Error Logs
    grep "$line" /home/eximlog >> $Elogs
done <"$Errors"

read is line oriented: it reads one line at a time.

Or, this may work for you and it doesn't need any looping at all:

 grep -f "$Errors" /home/eximlog

The -f options tells grep to read patterns from a file, one pattern per line.

Also, it looks to me like your error code patterns are fixed strings not regular expressions. In that is the case, to avoid unpleasant surprises, add the -F option to grep:

 grep -Ff "$Errors" /home/eximlog

edited Jun 8, 2016 at 6:38

answered Jun 8, 2016 at 6:18

John1024

76.4k12 gold badges176 silver badges165 bronze badges

2

Yes grep -f "$Errors" /home/eximlog works for me. thanks @John1024

blaCkninJa
– blaCkninJa

2016-06-08 06:45:47 +00:00
Commented Jun 8, 2016 at 6:45
1

was returning only one line for me, and I discovered this is due to CRLF line endings in the source file, so make sure you have it converted to Unix EOL

RAM237
– RAM237

2022-07-26 15:58:45 +00:00
Commented Jul 26, 2022 at 15:58

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