last revised 6 May 2009
| CSC 161 | Grinnell College | Spring, 2009 |
| Imperative Problem Solving and Data Structures | ||
Please read the following materials carefully:
The Bash shell allows users to interact with the computer through a terminal window, organizing commands that tie various programs together. First developed by Brian Fox in 1987, the Bash shell seeks to incorporate numerous features from earlier shells for the Unix operating system. In particular, the Bash shell draws upon the Bourne shell (developed by Ken Thompson and then Stephen Bourne around 1977), the Korn shell (developed by David Korn in the early 1980s), and the C shell (developed by Bill Joy, based on Thompson's earlier shells).
This history is particularly evident in the syntax allowed for if expressions. Bash allows interprets each syntax properly — but do not try to mix and match the different versions. The following examples illustrate acceptable Bash syntax, following two different ancesters.
| Task | Bourne shell style | Korn shell style |
|---|---|---|
| numeric test a > 0 |
if [ $a -gt \0 ]; then echo positive fi |
if (( $a > 0 )); then echo positive fi |
| numeric test a ≤ 0 |
if [ $a -le 0 ]; then echo non-positive else echo positive fi |
if (( $a <= 0 )); then echo non-positive else echo positive fi |
| numeric test a < 0 and a == 0 |
if [ $a -lt 0 ]; then echo negative elif [ $a -eq 0 ]; then echo zero else echo positive fi |
if (( $a <= 0 )); then echo non-positive elif (( $a == 0 )); then echo zero else echo positive fi |
| numeric test 0 ≤ a &le 10 |
if [ 0 -le $a -a $a -le 10 ]; then echo between 0 and 10 else echo not between 0 and 10 fi |
if (( (0 <= $a) && ($a <= 10) )); then echo between 0 and 10 else echo not between 0 and 10 fi |
For reference, all of these code segnments are available in the Bash shell bash-example-1
This document is available on the World Wide Web as
http://www.walker.cs.grinnell.edu/courses/161.sp09/readings/reading-linux-scripts.shtml
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created 21 April 2008 last revised 6 May 2009 |
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| For more information, please contact Henry M. Walker at walker@cs.grinnell.edu. |