Category:C Shell
This programming language may be used to instruct a computer to perform a task.
| Execution method: | Interpreted |
|---|---|
| Lang tag(s): | csh |
| See Also: |
|
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 Shell at /bin/csh. Hashbang lines should use the -f option:
<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C Shell is obsolete.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 (ls ~), job control, command history, and aliases, but POSIX shells now have all of those.
Csh Programming Considered Harmful and Top Ten Reasons not to use the C shell give multiple reasons to avoid C Shell.
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.
Syntax
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.
| C | C Shell |
|---|---|
| <lang c>#include <stdio.h>
int main() { int n; n = 13;
printf("%d\n", n);
while (n != 1) {
if (n % 2)
n = 3 * n + 1;
else
n /= 2;
printf("%d\n", n);
}
return 0; }</lang> |
<lang csh>
if ($n % 2) then @ n = 3 * $n + 1 else @ n /= 2 endif echo $n end
|
C Shell has no braces {} to group the commands. Strange keywords are then, endif and end. Expressions have $n instead of n. Assignments use @ n.
C Shell has "a C-like syntax" because C Shell is more like C than Bourne Shell.
| Bourne Shell | C Shell |
|---|---|
| <lang bash>n=13
echo $n while test $n -ne 1; do if expr $n % 2 >/dev/null; then n=`expr 3 \* $n + 1` else n=`expr $n / 2` fi echo $n done</lang> |
<lang csh>@ n = 13
echo $n while ($n != 1) if ($n % 2) then @ n = 3 * $n + 1 else @ n /= 2 endif echo $n end</lang> |
Bourne Shell requires test or expr 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 10 - 3 - 2 acts like 10 - (3 - 2). The fix is to use parentheses.
<lang csh>% @ n = 10 - 3 - 2 % echo $n 9 % @ n = (10 - 3) - 2 % echo $n 5</lang>
Links
- OpenBSD has csh(1) manual and source code.
Subcategories
This category has the following 3 subcategories, out of 3 total.
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- C Shell Implementations (empty)
- C Shell User (4 P)
Pages in category "C Shell"
The following 31 pages are in this category, out of 31 total.