Why does sh/bash set command line parameter values when trying to set environment variable?

Question

A question on basics : While tuning environment variables for a program launched from a script, I ended up with somewhat strange behaviour with sh (which seems to be actually linked to bash) : variable setting seems to mess up with command-line parameters.

Could somebody explain why does this happen?

A simple script:

#! /bin/sh

# Messes with $1 ??
set ANT_OPTS=-Xmx512M
export ANT_OPTS

# Works
# export ANT_OPTS=-Xmx512M

echo "0 = $0"
echo "1 = $1"

When I run this with the upper alternative (set + export), the result is as following:

$ ./test.sh foo
0 = ./test.sh
1 = ANT_OPTS=-Xmx512M

But with lower alternative (export straight), the result is as I supposed:

$ ./test.sh foo
0 = ./test.sh
1 = foo

There is surely logical explanation, I just haven't figured it out yet. Somebody who does have idea?

br, Touko

Solution 1

You should just use ANT_OPTS=-Xmx512M instead of set ANT_OPTS=-Xmx512M.

UPDATE: See here for discussion of set, and the manual.

Solution 2

"set" isn't part of setting variables in Bourne Shell. That should be

ANT_OPTS=-Xmx512m
export ANT_OPTS 

Comments

[Apollon]

OK, that also solves the behavior that I didn't expect. Thanks!

[Hank Gay]

1. As @Paul Tomblin mentions in a comment, if you're using #!/bin/sh you should restrict yourself to just Bourne Shell, but bash is what you're going to get from /bin/sh on pretty much every single Linux distro, so if you get bugs it might be because you used a bash-ism by accident. 2. If you're coming to bash from csh or similar, you should probably find a good book and dig in; it seems like bash was designed to confuse people who already know csh (and vice versa).