Chapter 10. Files

80

10.3 Shared libraries

This section has moved to `Shared libraries' on page

53

.

10.4 Scripts

All command scripts, including the package maintainer scripts inside the package and used

by

dpkg

, should have a

#!

line naming the shell to be used to interpret them.

In the case of Perl scripts this should be

#!/usr/bin/perl

.

Shell scripts (

sh

and

bash

) should almost certainly start with

set  e

so that errors are de 

tected. Every script should use

set  e

or check the exit status of every command.

The standard shell interpreter

/bin/sh

can be a symbolic link to any POSIX compatible shell,

if

echo  n

does not generate a newline.

4

Thus, shell scripts specifying

/bin/sh

as interpreter

should only use POSIX features. If a script requires non POSIX features from the shell inter 

preter, the appropriate shell must be specified in the first line of the script (e.g.,

#!/bin/bash

)

and the package must depend on the package providing the shell (unless the shell package is

marked  Essential , as in the case of

bash

).

You may wish to restrict your script to POSIX features when possible so that it may use

/bin

/sh

as its interpreter. If your script works with

dash

(originally called

ash

), it's probably

POSIX compliant, but if you are in doubt, use

/bin/bash

.

Perl scripts should check for errors when making any system calls, including

open

,

print

,

close

,

rename

and

system

.

csh

and

tcsh

should be avoided as scripting languages. See Csh Programming Considered

Harmful, one of the

comp.unix.*

FAQs, which can be found at

http://www.faqs.org/

faqs/unix faq/shell/csh whynot/

. If an upstream package comes with

csh

scripts

then you must make sure that they start with

#!/bin/csh

and make your package depend

on the

c shell

virtual package.

Any scripts which create files in world writeable directories (e.g., in

/tmp

) must use a mecha 

nism which will fail if a file with the same name already exists.

The Debian base system provides the

tempfile

and

mktemp

utilities for use by scripts for

this purpose.

10.5 Symbolic links

In general, symbolic links within a top level directory should be relative, and symbolic links

pointing from one top level directory into another should be absolute. (A top level directory

4

Debian policy specifies POSIX behavior for

/bin/sh

, but

echo  n

has widespread use in the Linux com 

munity (in particular including this policy, the Linux kernel source, many Debian scripts, etc.). This

echo  n

mechanism is valid but not required under POSIX, hence this explicit addition. Also, rumour has it that this shall

be mandated under the LSB anyway.