Understanding UNIX Shell Scripts

Special characters that can be used to manipulate commands in the command line include

1.    Backslash (\)

2.    Greater than (>)

3.    Less than (<)

4.    Pipe (|)

5.    Ampersand (&)

Backslash:

Character prevents the shell from treating another character as a special character through a process called backslash escaping.

This allows us to split a command statement across multiple lines. When we place the backslash at the end of a line and then press Enter, we can continue the statement on the next line. The backslash prevents the shell from treating the Enter keystroke – or new line character – as a special character.

For Example:

$echo Long pieces of test may not always fit onto to a single \

Line of the command line interface, so it becomes \

Necessary to split them across multiple lines using \

Backslashes.

Greater than (>):

Allows us to direct the standard output of a command to a file or a device such as a printer instead of to the terminal screen.

For Eample:

$ ls –l /usr/home > userdirs

Less than (<):

Allows us to send the contents of a file to a command as its standard output.

For Eg:

$ sort –d < list

Pipe line (|):

Direct the output of one command to the input of another command.

For Example:

$ cat good | grep ‘India’

Ampersand(&):

Character at the end of a command statement allows us to run commands in the background.

For Eg:

$ find / -name che &

[1]  48748

$ che

NOTE:

If we want to use special character in command line text without the shell recognizing them as special characters, we have to enclose them with a backslash (\).

For Example:

$echo Tours \& Accommodation

Tours & Accommodation

This eg shows an ‘echo’ command in which the ‘echo’ text contains an ampersand. There’s backslash

In front of the ampersand, which prevents the shell from treating it as a special character.