Erle Robotics Unix Introduction Gitbook Free

Searching the contents of a file

Simple searching using less

Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type

 less science.txt

then, still in less, type a forward slash [/] followed by the word to search

/science

As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.

grep (don't ask why it is called grep)

grep is one of many standard UNIX utilities. It searches files for specified words or patterns. First clear the screen, then type

 grep science science.txt

As you can see, grep has printed out each line containg the word science (without capital letters)

Try typing

 grep Science science.txt

The grep command is case sensitive; it distinguishes between Science and science.

To ignore upper/lower case distinctions, use the -i option, i.e. type

 grep -i science science.txt

To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type

grep -i 'spinning top' science.txt

Some of the other options of grep are:

-v display those lines that do NOT match -n precede each matching line with the line number -c print only the total count of matched lines Try some of them and see the different results. Don't forget, you can use more than one option at a time. For example, the number of lines without the words science or Science is

 grep -ivc science science.txt

wc (word count)

A handy little utility is the wccommand, short for word count. To do a word count on science.txt, type

 wc -w science.txt

To find out how many lines the file has, type

 wc -l science.txt

To finish, let's see some example of the commands.

working with erlerobot: