Brace expansion

Curly braces allow you to specify a set of characters from which the shell automatically forms all possible combinations. To make this work, the characters to be combined with the given string must be specified as a comma-separated list with no spaces:

    $ touch file{1,2,3}
    $ ls

    $ mkdir directory{1,2,3}{a,b,c}
    $ ls

    $ touch file{a..z}
    $ ls

The following is the summary of various I/O-redirection and logical operators:

For example:

    $ ls || echo "Command un-successful"
    $ ls a abcd || echo "Command un-successful"

These commands will print Command un-successful if the ls command is unsuccessful.