CIT 140: Introduction to IT Slide #1

CSC 140: Introduction to IT

UNIX Shells

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Objectives

• To describe what a UNIX shell is.

• To describe briefly some commonly used shells

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What is a shell?

A command interpreter.– Runs external commands like cp and rm.

– Built-in commands change shell environment:• cd – change directory

• VAR=value

– I/O redirection.• cat /etc/shells >shells

– Ease of use• Command line editing, tab completion, history.

– Programming• Conditionals, loops, etc.

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Environment Variables

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Shell Initialization Files

• Configure shell settings at login.– Create aliases.– Set environment variables.

• bash initialization files– /etc/profile System-wide for sh and bash.– /etc/bashrc System-wide for bash.– ~/.bashrc User startup file.

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sh/csh Differences

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Which Shell Suits Your Needs?

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sh/csh Similarities

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How to change your shell?

• Change your login shell.> chsh zsh

• Run the other shell directly> echo $SHELL

/bin/bash

> zsh

%

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Shell Metacharacters

• Non-alphanumeric characters that have special meaning to the shell.

• They cannot be used in shell commands.• Allow you to specify multiple files in

multiple directories in one command line.

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Globbing

• ?  Matches any one character.

• *  Matches zero or more characters.

• []  Matches list of characters inside brackets.

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Globbing> ls *htmlannounce.html guidelines.html readings.html sites.htmlassignments.html index.html schedule.html> cd assignments> ls a[2-3]?htmla2.html a3.html

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Command History

Up-arrow Previous command

Down-arrow Next command

history List old commands

!! Previous command

!# Command #

!$ Last arg of previous command

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Command line editing

Ctrl-a Beginning of line

Ctrl-e End of line

Left-arrow Move back one character

Right-arrow Move forward one character

Ctrl-u Erase line

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Filename completion

TAB Completes filename

TAB-TAB Show list of possible

completions.