← Shell Initiation

In our journey we are in the point where we already know the terrain, now it time to start walking.

The fist tools you are going to use regularly are those for viewing files

• echo Echo arguments to the standard options

• touch FILENAME Creates a blank file or modifies an existing file.s attributes.

• cat FILENAME Displays a filename.

• head FILENAME Shows the beginning of a file.

• tail FILENAME Shows the end of a file.

• more FILENAME Browses through a file from beginning to end.

• less FILENAME Browses through a file from end or beginning.

But viewing it's not enough. Isn't? Our terminal can act like a complete word processor. We will find that there are lot of programs that can process text.

• cmp Compare the contents of two files

• comm Compare sorted data

• cut Cut out selected fields of each line of a file

• diff Differential file comparator

• expand Expand tabs to spaces

• join Join files on some common field

• sort Sort file data

• split Split file into smaller files

• tr Translate characters

• uniq Report repeated lines in a file

• wc Count words, lines, and characters

• fmt Simple text formatter

• pico/nano Simple text editors

Sometimes this is just not enough and you need to do heavy regular expressions stuff. You will find two incredible tools for that:

• awk Pattern scanning and processing language. Reference: here

• sed stream text editor. References: here, here, here, here and here

Intact awk and sed have there own kind of language. With is not strange to find in Unix contents. There are other unix programs that have their own language (script language) that you can use directly from the terminal. Must of them you already know them if you have been doing web work:

• perl

• python

• php

Even more, all the commands we have seen can be put together inside a file with a specify header and be executed by the the same program that let you type commands on your terminal (bash):

The header will specify witch program will use to execute the script.

#!/bin/bash
# Proper header for a Bash script.

or

#!/usr/bin/python
# Proper header for a Python script.

or

#!/usr/bin/perl
# Proper header for a Python script.

Little by little you are getting how close are the internet and UNIX. Isn't? If you are interested on How to Programming Bash Scritps check this link of this other one

You will find that this scripts not only have IF and FOR statements that you can use also on your terminal directly, but also the possibility to mix commands by passing through them information. This are call pipes or redirections. That mean you can redirect the out put of one command to be the input of other one.

To do this plumbing magic you use the following simbols:

• pgm > file Output of pgm is redirected to file

• pgm < file Program pgm reads its input from file.

• pgm >> file Output of pgm is appended to file.

• n > file Output from stream with descriptor n redirected to file.

• n >> file Output from stream with descriptor n appended to file.

• n >& m Merge output from stream n with stream m.

• n <& m Merge input from stream n with stream m.

• << tag Standard input comes from here through next tag at start of line.

• | Takes output from one program, or process, and sends it to another.

You can found some amazing examples of very useful lines that involve redirection here

Another important duty you are going to do on your terminal will involve not just moving files from here to there but also compress them and package them. For that there are this tools.

• compress Compress files

• uncompress Uncompress files

• gunzip Uncompress gzipped files

• gzip GNU alternative compression method

• unzip List, test and extract compressed files in a ZIP archive

• zcat Cat a compressed file

• zcmp Compare compressed files

• zdiff Compare compressed files

• zmore File perusal filter for crt viewing of compressed text

There is one that's particularly powerful that let you pack and compress in different formats call tar for witch is worth it to do a

man tar

Speaking of power it's hard not to speak of two text editor that are SO incredible powerful that they can be use as IDEs and much more. This is the case of vi and emacs and the dived waters on their of developers choice. You can picture them as two doors to two different tribes. Choose wisely:

• Emacs

• Vi/vim