Shell Scripting

PAix · 11-02-2007, 03:58 PM

I read a white paper a few years back that explained at the time why batch programming should be done in sh (bash). Because in tcsh and ksh, while having perhaps richer instruction sets than plain old sh (bourne shell) the behaviour of some constructs tended to differ slightly between the batch and interactive execution of some scripts. Sh was simple, but considered very safe for batch. Just in case, and while your assembled audience awaits you posting the awk version info.

PAix

archtoad6 · 11-03-2007, 12:14 AM

Many people think that shell scripts should be written for sh, for portability.
OTOH, I learned shell scripting in bash & am not about to give up its richness.
If it ever (doubtful) gets to a point that someone really needs to run something of mine on a system that doesn't have bash,
they have 3 choices:

Install bash.
Do without.
Hire my friend Willie to re-write it.

bigearsbilly · 11-05-2007, 03:33 AM

I've never (in all my days) had any trouble running ksh in batch mode.

An annoying thing about linux is that even if you do a
#!/bin/sh it actually runs bash and it's not properly compatible.

so you get a linux bod wiriting a /bin/sh script that won't run on your solaris box
unless you swap it to /bin/ksh.
and when you explain it to them they don't get it.

Another reason is you'll find that on unix boxes the /bin/sh would be statically linked
so if all goes pear shaped it's more likey to work than other shells

nx5000 · 11-05-2007, 09:04 AM

Quote:

An annoying thing about linux is that even if you do a
#!/bin/sh it actually runs bash and it's not properly compatible.

Uhh no. This is only a problem (feature explained in man bash maybe?) of BASH.

Code:

aha@debian$ echo $0
bash
aha@debian$ ls -l /bin/sh
lrwxrwxrwx 1 root root 4 2007-10-01 12:06 /bin/sh -> dash
aha@debian$ cat listf 
#!/bin/bash
 for t in files links directories; do echo $t:`find . -type ${t:0:1} | wc -l`; done 2> /dev/null
aha@debian$ ./listf 
files:60
links:3
directories:2
aha@debian$ sed -i 's/bash/sh/' listf 
aha@debian$ ./listf 
./listf: 1: Syntax error: Bad substitution

This shows that /bin/sh was launched as requested.

bigearsbilly · 11-05-2007, 09:13 AM

ok, try this and I'll believe you, much simpler...

granted on cygwin, I'm at work, but...

Code:

$ uname -a
CYGWIN_NT-5.1 BTG142169 1.5.23(0.156/4/2) 2006-12-19 10:52 i686 Cygwin
$ /bin/sh
$ export X=Y

Code:

billym.>uname -a
SunOS primadtpdev 5.8 Generic_108528-20 sun4u sparc SUNW,Ultra-250
billym.>/bin/sh
billym.>export X=Y
X=Y: is not an identifier

unSpawn · 11-05-2007, 09:31 AM

Quote:

Originally Posted by archtoad6

Many people think that shell scripts should be written for sh, for portability. OTOH, I learned shell scripting in bash & am not about to give up its richness.

ROTFL, that was my stance as well. Then I stepped into this project and I had to unlearn a lot of things to stay compatible... For testing Bourne compatibility on GNU/Linux I use the Heirloom shell. Strict as hell.

nx5000 · 11-05-2007, 09:31 AM

Quote:

billym.>export X=Y
X=Y: is not an identifier

Wow that's ridiculous!!
I haven't got a Slow^H^H^H^HSunOs "easily" to connect to..
Is /bin/sh linked to something?

I remember when I was scripting for different Oses, a bit like doing html for different browsers..

Under cygwin or under busybox's sh or under my linux, I don't have the problem.

nx5000 · 11-05-2007, 09:32 AM

Quote:

Originally Posted by unSpawn

Then I stepped into this project and I had to unlearn a lot of things to stay compatible...

That exactly why I forced myself to link sh to dash, to discover all the "bashism" I had created.
Also because it's supposed to be faster.

bigearsbilly · 11-05-2007, 10:01 AM

it's annoying to try and explain to a supplier to change all their shebangs to ksh
they don't believe it either!

anyway most commercial Unix boxes have ksh (I think all I've used anyway) so I use that.
(I prefer ksh anyway)