110 lines
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3.2 KiB
Text
110 lines
No EOL
3.2 KiB
Text
{{language
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|exec=interpreted
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|tags=csh
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|hopl id=1936
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}}{{implementation|UNIX Shell}}
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'''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]].
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BSD keeps the C Shell at <code>/bin/csh</code>. [[Hashbang]] lines should use the -f option:
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<lang csh>#!/bin/csh -f</lang>
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== Reputation ==
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C Shell is obsolete.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>), job control, command history, and aliases, but POSIX shells now have all of those.
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[http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/ Csh Programming Considered Harmful] and [http://www.grymoire.com/Unix/CshTop10.txt Top Ten Reasons not to use the C shell] give multiple reasons to avoid C Shell.
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tcsh is a later version that fixed many of the problems with csh. It is still actively, if intermittently, maintained and has a following such as on Solaris.
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== Syntax ==
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[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.
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This example prints a [[Hailstone sequence]] from 13.
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{| class="wikitable"
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! C
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! C Shell
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|-
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|| <lang c>#include <stdio.h>
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int
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main()
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{
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int n;
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n = 13;
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printf("%d\n", n);
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while (n != 1) {
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if (n % 2)
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n = 3 * n + 1;
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else
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n /= 2;
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printf("%d\n", n);
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}
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return 0;
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}</lang>
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|| <lang csh>
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@ n = 13
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echo $n
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while ($n != 1)
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if ($n % 2) then
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@ n = 3 * $n + 1
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else
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@ n /= 2
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endif
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echo $n
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end
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</lang>
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|}
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C Shell has no braces {} to group the commands. Strange keywords are <code>then</code>, <code>endif</code> and <code>end</code>. Expressions have <code>$n</code> instead of <code>n</code>. Assignments use <code>@ n</code>.
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C Shell has "a C-like syntax" because C Shell is more like C than [[Bourne Shell]].
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{| class="wikitable"
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! Bourne Shell
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! C Shell
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|-
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|| <lang bash>n=13
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echo $n
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while test $n -ne 1; do
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if expr $n % 2 >/dev/null; then
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n=`expr 3 \* $n + 1`
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else
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n=`expr $n / 2`
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fi
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echo $n
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done</lang>
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|| <lang csh>@ n = 13
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echo $n
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while ($n != 1)
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if ($n % 2) then
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@ n = 3 * $n + 1
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else
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@ n /= 2
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endif
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echo $n
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end</lang>
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|}
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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.
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<lang csh>% @ n = 10 - 3 - 2
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% echo $n
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9
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% @ n = (10 - 3) - 2
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% echo $n
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5</lang>
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== Links ==
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* [[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]. |