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Category:C Shell: Difference between revisions
Fill 'Syntax' and 'Reputation' sections.
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(Fill 'Syntax' and 'Reputation' sections.) |
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{{language
|exec=interpreted
|tags=csh}}{{implementation|UNIX Shell}}
'''csh''' was the shell that William Joy wrote for [[BSD]]. '''csh''' accepted the same [[Unix]] commands as other shells, but had a very different syntax (for variable assignments, control flow, and such). '''csh''' is not compatible with the [[Bourne Shell]].
BSD keeps the C
<lang csh>#!/bin/csh -f</lang>
== Reputation ==
C Shell is obsolete. Most scriptwriters prefer a Bourne-compatible shell, and few users want to learn two flavors of shells. C Shell introduced tilde expansion (<code>ls ~</code>), history recall, job control and aliases, but POSIX shells now have all of those.
== Syntax ==
[http://www.openbsd.org/cgi-bin/man.cgi?query=csh&apropos=0&sektion=1&manpath=OpenBSD+Current&arch=i386&format=html The manual for csh(1)] claims that C Shell has "a C-like syntax". Several other languages have a C-like syntax, including [[Java]] and [[Pike]], and Unix utilities [[AWK]] and [[bc]]. C Shell is less like [[C]] than those other languages.
This example prints a [[Hailstone sequence]] from 13.
{| class="wikitable"
! C
! C Shell
! Bourne Shell▼
|-
|| <lang c>#include <stdio.h>
Line 55 ⟶ 62:
</lang>
|}
|| <lang bash>▼
C Shell has no braces {} to group the commands. Strange keywords are <code>then</code>, <code>endif</code> and <code>end</code>. Expressions have <code>$n</code> instead of <code>n</code>. Assignments use <code>@ n</code>.
C Shell has "a C-like syntax" because C Shell is more like C than [[Bourne Shell]].
{| class="wikitable"
▲! Bourne Shell
! C Shell
|-
▲|| <lang bash>n=13
echo $n
while test $n -ne 1; do
Line 71 ⟶ 81:
fi
echo $n
done</lang>
echo $n
while ($n != 1)
</lang>▼
if ($n % 2) then
@ n = 3 * $n + 1
else
@ n /= 2
endif
echo $n
▲end</lang>
|}
Bourne Shell requires <code>test</code> or <code>expr</code> to evaluate expressions. C Shell has built-in expressions, so the Hailstone sequence comes more easily. These expressions have a stupid quirk: all operators are right-associative, so <code>10 - 3 - 2</code> acts like <code>10 - (3 - 2)</code>. The fix is to use parentheses.
<lang csh>% @ n = 10 - 3 - 2
% echo $n
9
% @ n = (10 - 3) - 2
▲<lang csh>% @ n = (10 - 3) - 2
% echo $n
5</lang>
== Links ==
* [[OpenBSD]] has [http://www.openbsd.org/cgi-bin/man.cgi?query=csh&apropos=0&sektion=1&manpath=OpenBSD+Current&arch=i386&format=html csh(1) manual] and [http://www.openbsd.org/cgi-bin/cvsweb/src/bin/csh/ source code].
▲* [http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/ Csh Programming Considered Harmful]
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