Bourne Shell: Difference between revisions
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The '''[[wp:Bourne Shell|Bourne Shell]]''' is a [[Unix]] shell upon which many shells are based; notably the [[wp:Korn shell|Korn shell]] and [[Bourne Again SHell]]. (The other major tree of Unix shells descend from [[csh]].)
'''Portable Shell Syntax''' is the scripting language syntax used by the [[wp:UNIX System V|System V]] Bourne shell. This syntax is compatible with the heirloom shell and is the syntax documented in most Unix books. Examples marked "Works with: Bourne Shell" should work in any of the Bourne-compatible shells.
A Bourne Shell script begins with a [[wp:shebang (Unix)|shebang]] (also known as a ''hashbang'') like this, which tells the operating system to use the Bourne compatible shell interpreter:
<syntaxhighlight lang="sh">
</syntaxhighlight>
In 2009, ''[[wp:Computerworld|Computerworld]]'' published an in-depth interview with Steve Bourne,
== Bugs ==
Bourne Shell and Heirloom Shell have problems with here documents. Here is one such problem. A substitution, inside a here document, inside backquotes, inside double quotes, does insert too many backslashes.
<syntaxhighlight lang="sh">f() {
cat <<!
here $1
!
}
expr "`f string`"
# Output from Bourne Shell: here \s\t\r\i\n\g
# Correct output: here string</syntaxhighlight>
The workaround is to move the backquotes to an assignment.
<syntaxhighlight lang="sh">f() {
cat <<!
here $1
!
}
var=`f string`
expr "$var"
# Output: here string</syntaxhighlight>
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Latest revision as of 12:35, 5 July 2023
The Bourne Shell is a Unix shell upon which many shells are based; notably the Korn shell and Bourne Again SHell. (The other major tree of Unix shells descend from csh.)
Portable Shell Syntax is the scripting language syntax used by the System V Bourne shell. This syntax is compatible with the heirloom shell and is the syntax documented in most Unix books. Examples marked "Works with: Bourne Shell" should work in any of the Bourne-compatible shells.
A Bourne Shell script begins with a shebang (also known as a hashbang) like this, which tells the operating system to use the Bourne compatible shell interpreter:
#!/bin/sh
In 2009, Computerworld published an in-depth interview with Steve Bourne, "The A-Z of Programming Languages: Bourne shell, or sh", which details the Bourne shell origins and design decisions.
Bugs
Bourne Shell and Heirloom Shell have problems with here documents. Here is one such problem. A substitution, inside a here document, inside backquotes, inside double quotes, does insert too many backslashes.
f() {
cat <<!
here $1
!
}
expr "`f string`"
# Output from Bourne Shell: here \s\t\r\i\n\g
# Correct output: here string
The workaround is to move the backquotes to an assignment.
f() {
cat <<!
here $1
!
}
var=`f string`
expr "$var"
# Output: here string