grep Bash中if语句的2个单词

Question

I am trying to see if my nohup file contains the words that I am looking for. If it does, then I need to put that into tmp file.

So I am currently using:

if  grep -q "Started|missing" $DIR3/$dirName/nohup.out
then
  grep -E "Started|missing" "$DIR3/$dirName/nohup.out" > tmp
fi

But it never goes into the if statement even if there are words that I am looking for.

How can I fix this?

Answer 1

Since basic sed uses BRE , regex alternation operator is represented by \\| . | matches a literal | symbol. And you don't need to touch | symbol in the grep which uses ERE .

if grep -q "Started\|missing" $DIR3/$dirName/nohup.out

Answer 2

You should use egrep instead of grep (Avinash Raj has explained that in other words already in his answer).

I would generally recommend using egrep as a default for everyday use (even though many expressions only contain the basic regular expression syntax). From a practical point the standard grep is only interesting for performance reasons.

Details about the advantages of grep vs. egrep can be found in that superuser question .

Answer 3

When you only put the grep results into the tmp-file, you do not want to grep the file twice.
You can not use

egrep "Started|missing" $DIR3/$dirName/nohup.out > tmp

since that would create an empty tmp file when nothing is found. You can remove empty files with if [ ! -s tmp ] if [ ! -s tmp ] or use another solution:

Redirectong the grep results without grepping again can be done with

rm -f tmp 2>/dev/null
egrep "Started|missing" $DIR3/$dirName/nohup.out | while read -r strange_line; do
   echo "${strange_line}" >> tmp
done