The diff command displays two files and prints the lines that are different.

# To view the differences between two files:
diff -u version1 version2

# To view the differences between two directories:
diff -ur folder1/ folder2/

# To ignore the white spaces:
diff -ub version1 version2

# To ignore the blank lines:
diff -uB version1 version2

# To ignore the differences between uppercase and lowercase:
diff -ui version1 version2

# To report whether the files differ:
diff -q version1 version2

# To report whether the files are identical:
diff -s version1 version2

# To diff the output of two commands or scripts:
diff <(command1) <(command2)

# To compare two files ignoring differences in the case of the letters and blank spaces:
diff -iw version1 version2