LPI Linux Certification in a Nutshell, 2nd Edition

Objective 2: Process Text Streams Using Filters

Many of the commands on Linux systems are intended to be used as filters, which modify text in helpful ways. Text fed into the command's standard input or read from files is modified in some useful way and sent to standard output or to a new file leaving the original source file unmodified. Multiple commands can be combined to produce text streams, which are modified at each step in a pipeline formation. This section describes basic use and syntax for the filtering commands important for Exam 101. Refer to a Linux command reference for full details on each command and the many other available commands.

cut

Syntax

cut options [files]

Description

Cut out (that is, print) selected columns or fields from one or more files. The source file is not changed. This is useful if you need quick access to a vertical slice of a file. By default, the slices are delimited by a tab character.

Frequently used options

-b list

Print bytes in list positions.

-c list

Print characters in list columns.

-d delim

Set field delimiter for -f.

-f list

Print list fields.

Example

Show usernames (in the first colon-delimited field) from /etc/passwd:

$ cut -d: -f1 /etc/passwd

expand

Syntax

expand [options] [files]

Description

Convert tabs to spaces. Sometimes the use of tab characters can make output that is attractive on one output device look bad on another. This command eliminates tabs and replaces them with the equivalent number of spaces. By ...