Bash-Prog-Intro-HOWTO.pdf

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BASH Programming - Introduction HOW-TO
BASH Programming − Introduction HOW−TO
BASH Programming − Introduction HOW−TO
Table of Contents
BASH Programming − Introduction HOW−TO .............................................................................................1
by Mike G mikkey at dynamo.com.ar .....................................................................................................1
1. Introduction. ..........................................................................................................................................1
2. Very simple Scripts. ..............................................................................................................................1
3. All about redirection. ............................................................................................................................1
4. Pipes. .....................................................................................................................................................1
5. Variables. ..............................................................................................................................................2
6. Conditionals. .........................................................................................................................................2
7. Loops for, while and until. ....................................................................................................................2
8. Functions. ..............................................................................................................................................2
9. User interfaces. .....................................................................................................................................2
10. Misc. ...................................................................................................................................................2
11. Tables. .................................................................................................................................................3
12. More Scripts. .......................................................................................................................................3
13. When something goes wrong (debugging). ........................................................................................3
14. About the document. ...........................................................................................................................3
1. Introduction. ..........................................................................................................................................3
1.1 Getting the latest version ...................................................................................................................3
1.2 Requisites. ..........................................................................................................................................4
1.3 Uses of this document. .......................................................................................................................4
2. Very simple Scripts. ..............................................................................................................................4
2.1 Traditional hello world scrip. ............................................................................................................4
2.2 A very simple backup script ..............................................................................................................4
3. All about redirection. ............................................................................................................................5
3.1 Theory and quick reference. ..............................................................................................................5
3.2 Sample: stdout 2 file .........................................................................................................................5
3.3 Sample: stderr 2 file . .........................................................................................................................5
3.4 Sample: stdout 2 stderr ......................................................................................................................6
3.5 Sample: stderr 2 stdout .....................................................................................................................6
3.6 Sample: stderr and stdout 2 file . .......................................................................................................6
4. Pipes. .....................................................................................................................................................6
4.1 What they are and why you'll want to use them. ...............................................................................7
4.2 Sample: simple pipe with sed ...........................................................................................................7
4.3 Sample: an alternative to ls −l *.txt . .................................................................................................7
5. Variables. ..............................................................................................................................................7
5.1 Sample: Hello World! using variables. ..............................................................................................7
5.2 Sample: A very simple backup script (little bit better). .....................................................................8
5.3 Local variables. ..................................................................................................................................8
6. Conditionals. .........................................................................................................................................9
6.1 Dry Theory. ........................................................................................................................................9
6.2 Sample: Basic conditional example if .. then.. ...................................................................................9
6.3 Sample: Basic conditional example if .. then ... else .......................................................................10
6.4 Sample: Conditionals with variables. ..............................................................................................10
7. Loops for, while and until. ..................................................................................................................10
7.1 For sample.. ......................................................................................................................................10
7.2 C−like for. ........................................................................................................................................11
7.3 While sample ...................................................................................................................................11
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BASH Programming − Introduction HOW−TO
Table of Contents
7.4 Until sample. ....................................................................................................................................11
8. Functions. ............................................................................................................................................12
8.1 Functions sample. ............................................................................................................................12
8.2 Functions with parameters sample. ..................................................................................................12
9. User interfaces. ...................................................................................................................................13
9.1 Using select to make simple menus. ................................................................................................13
9.2 Using the command line . ................................................................................................................13
10. Misc. .................................................................................................................................................14
10.1 Reading user input with read. ........................................................................................................14
10.2 Arithmetic evaluation. ....................................................................................................................14
10.3 Finding bash. .................................................................................................................................15
10.4 Getting the return value of a program. ...........................................................................................16
10.5 Capturing a commands output . .....................................................................................................16
10.6 Multiple source files. .....................................................................................................................16
11. Tables. ...............................................................................................................................................16
11.1 String comparison operators. .........................................................................................................16
11.2 String comparison examples. .........................................................................................................17
11.3 Arithmetic operators. .....................................................................................................................17
11.4 Arithmetic relational operators. .....................................................................................................18
11.5 Useful commands.. .........................................................................................................................18
12. More Scripts. .....................................................................................................................................22
12.1 Applying a command to all files in a directory.. ...........................................................................22
12.2 Sample: A very simple backup script (little bit better). .................................................................22
12.3 File re−namer. ................................................................................................................................23
12.4 File renamer (simple). ....................................................................................................................24
13. When something goes wrong (debugging). ......................................................................................25
13.1 Ways Calling BASH . ....................................................................................................................25
14. About the document. .........................................................................................................................25
14.1 (no) warranty. .................................................................................................................................25
14.2 Translations. ...................................................................................................................................25
14.3 Thanks to.. ......................................................................................................................................26
14.4 History ...........................................................................................................................................26
14.5 More resources.. .............................................................................................................................26
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BASH Programming − Introduction HOW−TO
by Mike G mikkey at dynamo.com.ar
Thu Jul 27 09:36:18 ART 2000
This article intends to help you to start programming basic−intermediate shell scripts. It does not intend to
be an advanced document (see the title). I am NOT an expert nor guru shell programmer. I decided to write
this because I'll learn a lot and it might be useful to other people. Any feedback will be apreciated, specially
in the patch form :)
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4. Pipes
BASH Programming − Introduction HOW−TO
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BASH Programming − Introduction HOW−TO
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10. Misc
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5.Variables
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