If the csh were really C-like, you would expect to be able to safely employ this kind of logic. Consider the common C construct:.
Undefined variables are not fatal errors in the Bourne shell, so this issue does not arise there. While the csh does have built-in expression handling, it's not what you might think. In fact, it's space sensitive. This is an error. Wouldn't it be nice to know you had an error in your script before you ran it? That's what the -n flag is for: just check the syntax.
This is especially good to make sure seldom taken segments of code code are correct. Alas, the csh implementation of this doesn't work. Consider this statement:. The csh tells you there's nothing wrong with this script. The equivalent construct in the Bourne shell, on the other hand, tells you this:. If you have an alias with backquotes, and use that in backquotes in another one, you get a coredump.
While some vendors have fixed some of the csh's bugs the tcsh also does much better here , many have added new ones. Most of its problems can never be solved because they're not actually bugs per se, but rather the direct consequences of braindead design decisions.
It's inherently flawed. Do yourself a favor, and if you have to write a shell script, do it in the Bourne shell. It's on every UNIX system out there. However, behavior can vary. The Korn shell is the preferred programming shell by many sh addicts, but it still suffers from inherent problems in the Bourne shell's design, such as parsing and evaluation horrors.
The Korn shell or its public-domain clones and supersets like bash aren't quite so ubiquitous as sh, so it probably wouldn't be wise to write a sharchive in them that you post to the net. When Until then, we'll be stuck with bug-incompatible versions of the sh lying about. The Plan 9 shell, rc, is much cleaner in its parsing and evaluation; it is not widely available, so you'd be sacrificing portability.
No vendor is shipping it yet. Some vendors even ship it standard. Why is the default not float? Hello, I am trying to learn Networking Programming in C in unix enviorment. I want to know how good it is to become a network programmer.
Anybody experienced Network Programmer, please tell me is my I have an extraordinary problem with a csh script This second csh script is below. RedHat Commands.
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View Public Profile for bigearsbilly. Find all posts by bigearsbilly. View Public Profile for kristinu. Find all posts by kristinu. The closes there were in case something really cared about all its FDs. We send stderr to sed, and then put it back out 2. But if you want it from A, you're out of luck -- if you're in the csh , that is. In the Bourne shell, you can get it, although doing so is a bit tricky. The csh is a horrid botch with its built-ins.
You can't put them together in many reasonable way. Just make sure you have another window handy. You can't combine multiline constructs in a csh using semicolons. There's no easy way to do this alias cmd 'if foo then bar; else snark; endif'. In the Bourne shell, you can trap any signal, or the end-of-program exit. This makes it really hard to construct strings with mixed quotes in them. In the Bourne shell, this works just fine. Dollar signs cannot be escaped in double quotes in the csh.
You have to use backslashes for newlines, and it's just darn hard to get them into strings sometimes. Say what? You don't have these problems in the Bourne shell, where it's just fine to write things like this: echo 'This is some text that contains several newlines.
There's this big difference between global environment and local shell variables. In csh , you use a totally different syntax to set one from the other.
You can't use :t, :h, etc on envariables.
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