GNU/Linux Command-Line Tools Summary

   GNU/Linux Command-Line Tools Summary
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11.2. Text Viewing Tools

• head
   

With no options it shows the first ten lines of a text file.

Use head -n x (where "x" is a number) to display the first x lines.

Try head -F to use a continually updated version of head (if the file changes it will be reloaded and displayed), please note that using this option will run head is a continuous loop so you'll need to use CTRL -C to exit.

For example:


   

head -n 20 somelog.txt

Will display the top 20 entries of the file "somelog.txt".



• tail
   

With no options it shows the last ten lines of a file.

Use tail -n x (where "x" is a number) to display the last x lines.

Try tail -F to use a continually updated version of tail (if the file changes it will be reloaded and displayed), please note that using this option will run tail is a continuous loop so you'll need to use CTRL -C to exit.

For example:


   

tail -n 20 somelog.txt

Will display the last 20 entries of the file "somelog.txt".



• less
   

Views text, can scroll backwards and forwards. Has many different options which are all described in the manual page.

When less is already running, use :n and :p (type a colon then the character) to move to the next and previous files (when there are multiple open files).

Command syntax:


   

less filename.txt

Or using a tool (in this example cat ):


   

cat file.txt | less




• more
   

Displays text, one page full at a time, more limited than less . In this case less is better than more .


   

more filename.txt

Or using a tool (is this example cat):


   

cat file.txt | more




• cat
   

Combines (concatenates) multiple documents into one document. Can be used on individual files as well.

Some useful options:

• -b --- number all non-blank lines

• -n --- number all lines.

Also try using nl to number lines (it can do more complex numbering), you will find it under under this section, Section 11.4

Example:


   

cat filepart1 filepart2 filepart3 > wholefile.txt

This will combine (concatenate) filepart1, filepart2 and filepart3 into the single file "wholefile.txt".



• tac
   

Combines (concatenates) multiple documents into one document and outputs them in reverse order. Can also be used on individual files. Notice that tac is cat written backwards.

Example:


   

tac filepart1 filepart2 filepart3 > wholefile.txt

This will combine (concatenate) filepart1, filepart2 and filepart3 into the single file but have each of the files written in reverse.



• z* commands
   

Many commands can be prefixed with a "z" to read/work within a gzip compressed file.

Some examples are zcat, zless, zmore, zgrep, zcmp, zdiff .

There are many utilities for working with text within compressed files without trying to manually de-compress them somewhere first...most begin with a "z". You will find some of them mentioned over here, Section 15.3 .



• bz*

* License

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