Scripting on Linux

Question

I am trying to create a script that will run a program on each file in a list. I have been trying to do this using a .csh file (I have no clue if this is the best way), and I started with something as simple as hello world

echo "hello world"

The problem is that I cannot execute this script, or verify that it works correctly. (I was trying to do ./testscript.csh which is obviously wrong). I haven't been able to find anything that really explains how to run C Scripts, and I'm guessing there's a better way to do this too. What do I need to change to get this to work?

faqs.org/faqs/unix-faq/shell/csh-whynot

William Pursell
– William Pursell

2011-07-13 17:58:18 +00:00
Commented Jul 13, 2011 at 17:58 — William Pursell
– William Pursell, Commented Jul 13, 2011 at 17:58

geekosaur · Accepted Answer · 2011-07-12 19:42:04Z

4

You need to mark it as executable; Unix doesn't execute things arbitrarily based on extension.

chmod +x testscript.csh

Also, I strongly recommend using sh or bash instead of csh, or you will soon learn about the idiosyncrasies of csh's looping and control flow constructs (some things only work inside them if done a particular way, in particular with the single-line versions things are very limited).

answered Jul 12, 2011 at 19:42

geekosaur

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Fred Foo Over a year ago

chmod works, but only because the file is also a valid Bourne shell script.

Drav Sloan · Accepted Answer · 2011-07-12 19:55:17Z

2

You can use ./testscript.csh. You will however need to make it executable first:

chmod u+x testscript.csh

Which means set testscript to have execute permissions for the user (who ever the file is owned by - which in this case should be yourself!)

Also to tell the OS that this is a csh script you will need put

 #! /path/to/csh

on the first line (where /path/to/csh is the full path to csh on your system. You can find that out by issuing the command which csh).

That should give you the behvaiour you want.

EDIT As discussed in some of the comments, you may want to choose an alternative shell to C Shell (csh). It is not the friendliest one for scripting.

edited Jul 12, 2011 at 19:55

answered Jul 12, 2011 at 19:43

Drav Sloan

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user405725 Over a year ago

+1. BTW this #! is called a shebang - en.wikipedia.org/wiki/Shebang_%28Unix%29

Keith Thompson · Accepted Answer · 2011-07-29 16:18:38Z

You have several options.

You can run the script from within your current shell. If you're running csh or tcsh, the syntax is source testscript.csh. If you're running sh, bash, ksh, etc., the syntax is . ./testscript.sh. Note that I've changed the file name suffix; source or . runs the commands in the named file in your current shell. If you have any shell-specific syntax, this won't work unless your interactive shell matches the one used by the script. If the script is very simple (just a sequence of simple commands), that might not matter.

You can make the script an executable program. (I'm going to repeat some of what others have already written.) Add a "shebang" as the first line. For a csh script, use #!/bin/csh -f. The -f avoids running commands in your own personal startup scripts (.cshrc et al), which saves time and makes it more likely that others will be able to use it. Or, for a sh script (recommended), used #!/bin/sh (no -f, it has a completely different meaning). In either case, run chmod +x the_script, then ./the_script.

There's a trick I often use when I want to perform some moderately complex action. Say I want to delete some, but not all, files in the current directory, but the criterion can't be expressed conveniently in a single command. I might run ls > tmp.sh, then edit tmp.h with my favorite editor (mine happens to be vim). Then I go through the list of files and delete all the ones that I want to leave alone. Once I've done that, I can replace each file name with a command to remove it; in vim, :%s/.*/rm -f &/. I add a #!/bin/sh at the top save it, chmod +x foo.sh, then ./foo.sh. (If some of the file names might have special characters, I can use :%s/.*/rm -f '&'/.)

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