Issue when doing a loop

UNIX for Beginners Q & A
1

Hi,

I just have started learning shell scripting (sh). Why do i only get the date?

while read dt
do
   echo "Date : ${dt}
   sed -n '/${dt}/,/${dt}/p' file1.log | grep -w ERROR
done < date1.dat

INPUT - date1.dat

2019-04-05 04:58:25
2019-04-05 04:58:26
2019-04-05 05:00:56
2019-04-05 05:08:26
2019-04-05 05:14:08
2019-04-05 05:21:26
2019-04-05 05:31:08

Desired Output

Date : 2019-04-05 04:58:25
2019-04-05 04:58:25,696 [Timer-7] ERROR :  421 Exceeded allowable connection time, disconnecting.

Actual Output

Date : 22019-04-05 04:58:25
Date : 22019-04-05 04:58:26
Date : 22019-04-05 05:00:56
Date : 22019-04-05 05:08:26
Date : 22019-04-05 05:14:08
Date : 22019-04-05 05:21:26
Date : 22019-04-05 05:31:08
2

The sed does not find anything.
Your mistake is the 'ticks' around $dt, but the shell only expands $dt within "quotes".
Further, a /x/,/x/ range is always one line, so you can simply address it with one /x/ .
Further, consider searching only at the beginning of the lines, by means of /^x/ , here /^$dt/ or /^${dt}/
Further, you can save the invocation of grep.

sed -n "/ERROR/!d; /^$dt/p" file1.log

or

sed "/ERROR/!d; /^$dt/!d" file1.log

Note: in bash you need to turn off history substitution with comand set +H .

1 Like
3

Thank you MadeInGermany.
Do i always need to turn off history substitution?

4

Only in an interactive bash shell (i.e. the command line), an exclamation mark followed by an alphanumeric character does history substitution.
For example

echo "!1"

prints line 1 from the command history .
Fortunately a bash script never does history substitution; a set +H work-around is not needed there.

1 Like