Differences

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+====== Set Intersection / Set Subtraction ======
+To find lines that are in both of two files (intersection) or in only one of the two files (subtraction), use the following commands:
+<code bash>
+# intersection of file1 and file2
+grep -xF -f file1 file2
+# subtraction of file1 from file2
+grep -vxF -f file1 file2
+</code>
+====== Trim Commented and Blank Lines ======
+Many Linux configuration files use the hash sign (''#'') as a comment indicator. The following command:
+<code bash>
+grep -v -e "^#" -e "^$" /etc/squid3/squid.conf
+</code>
+will remove (''-v'') all the lines starting with comments (''^#'') and then additionally will remove blank lines left after the trim (''^$'') from the file ''/etc/squid3/squid.conf''.