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Displaying only the matched pattern : By default, grep displays the entire line which has the matched string. We can make the grep to display only the matched string by using the -o option. 6. Show line number while displaying the output using grep -n : To show the line number of file with the line matched.
When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. Use the = operator with the test [ command. Use the == operator with the [[ command for pattern matching.
Testing $? is an anti-pattern.
if ./somecommand | grep -q 'string'; then
echo "matched"
fi
Test the return value of grep:
./somecommand | grep 'string' &> /dev/null
if [ $? == 0 ]; then
echo "matched"
fi
which is done idiomatically like so:
if ./somecommand | grep -q 'string'; then
echo "matched"
fi
and also:
./somecommand | grep -q 'string' && echo 'matched'
Another option is to check for regular expression match on the command output.
For example:
[[ "$(./somecommand)" =~ "sub string" ]] && echo "Output includes 'sub string'"
A clean if/else conditional shell script:
if ./somecommand | grep -q 'some_string'; then
echo "exists"
else
echo "doesn't exist"
fi
This looks more obvious, doesn't it?
# Just a comment... Check if output of command is hahaha
MY_COMMAND_OUTPUT="$(echo hahaha)"
if [[ "$MY_COMMAND_OUTPUT" != "hahaha" ]]; then
echo "The command output is not hahaha"
exit 2
else
echo "The command output is hahaha"
fi
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