You can use AWK or grep

awk '/error/' logfilename.txt

or grep

grep 'pattern' logfilename.txt

This example will show you all the fixed strings:

grep -F 'pattern' file 

The example below finds the word '_configuration' in *.cs files and writes the filename and the found text

find . -name "*.cs" -exec awk '/_configuration/ { print FILENAME ": " $0 }' {} +