Search for specified strings within files using extended regular expressions.
The egrep command is used to search for specified strings within files. The execution effect of egrep is similar to grep -E. Its syntax and parameters are the same as the grep command. The difference lies in how the pattern is interpreted: egrep uses extended regular expression (ERE) syntax, while grep uses basic regular expression (BRE) syntax. Extended regular expressions are more powerful and standardized than basic regular expressions.
egrep [options] [pattern] [file1, file2, ...]
Display lines in files that match the criteria. For example, to find files containing the string "Linux" in the current directory:
egrep Linux *
Result:
# Lines containing "Linux" in testfile
testfile:hello Linux!
testfile:Linux is a free Unix-type operating system.
testfile:This is a Linux testfile!
testfile:Linux
testfile:Linux
# Lines containing "Linux" in testfile1
testfile1:helLinux!
testfile1:This a Linux testfile!
# Lines containing "Linux" in testfile_2
testfile_2:Linux is a free unix-type opterating system
testfile_2:Linux test
Filter out comment lines and blank lines:
egrep -v '^\s*(#|$)' filename