About tilde expansion

This post is based on the bash tilde expansion documentation.

• Let's say that you enter several letters, and them the ~ (tilde) character.
• If non of the letters are quoted, then bash will try to treat these letters as a login name.
  It will then try to replace the tilde expression with the home …

About Brace Expansions

This post is based on the documentation of bash brace expansion.

• Brace expansion is a mechanism that creates strings
• The basic syntax is:
  • optional preanble (an opening string)
    • a series of comma-separated strings or
    • a sequence expression between a pair of braces
  • optional postscript (a …

Shell Operation

Covered here in bash documentation.

1. The shell reads its input from one of these:

• an input from a file
• from a string supplied as an argument to the -c invocation option
• from the user’s terminal

2. Breaks the input into words and operators, obeying the quoting rules described in Quoting

• These …

BASH Arrays

See here.

Indexed arrays

1names[0]=Yoesf
2names[1]=David
3echo $names        # will show: Yosef
4echo ${names[1]}   # will show: David

Assigning complete arrays. This is done by surounding a list of word with parentheses:

1-> girlz=(Betty Liza Jane)
2-> echo ${girlz[2]}
3Jane
4-> echo ${girlz}
5 …

Doing logic with [[ and ]]

(this topic is covered in the bash manual here)

• Return a status of 0 or 1 depending on the evaluation of the bash conditional expressions
• example 1: is this a file?

 1$> 
 2$> ls -l
 3total 4
 4-rw-rw-r-- 1 osboxes osboxes 6 Jan 21 08:39 myfile
 5$> 
 6$> [[ -f myfile ]]
 7 …

Pipelines

(this is covered in the bash manual here)

• A pipeline is a sequence of one or more commands separated by one of the control operators:
  |
  or
  |&
• The output of each command in the pipeline is connected via a pipe to the input of the next command.
  (if you want you can read more about pipes)
• These could be …

Introduction

• intro

• Hello World

• Parameters

• Special Parameters

• File Streams

• Bash Logic 1: pipelines and lists

• Bash Logic 2: Doing logic with [[ and ]]

• Bash Arrays

• Bash Expansions:

  • About Shell Expansions

  • Brace Expansion

  • Tilde Expansion

  • parameter and …

streams

• In UNIX, many things take the form of a stream of bytes.
• Real files are like that, because we can read the as a stream of bytes.
• Each process see a private list of streams that the process can access
• There is a number for each stream used:
  0,1,2,3,4….
  These numbers are called file descriptors
• The first 3 …