Question

How to pass a regular expression as a parameter to a shell script?

I need to write a shell script, which will take parameters and give them to unix commands. And I’d like to use regular expressions there. Is this possible at all?

Or reformulation – how to write the script equivalent to “cp” command, using only this command?

I’m trying to make a file “mycp”

#!/bin/bash -fx
cp $2 $1 

and call it by

mycp myDir "*sh" 

and want it to do the same as “cp *sh myDir”.
But resulting bash interpretation is:

+ cp '*sh' myDir
cp: *sh: No such file or directory

Answer 1

Revised question

I’m trying to make a file "mycp"

#!/bin/bash -fx
cp $2 $1 

and call it by

mycp myDir "*sh" 

In that case, you still need eval, but you’d write:

#!/bin/bash -x
eval cp "$2" "$1"

You’re running into problems because you have specified the -f option. man bash says (in part):

After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?, and [.

Remove the f from the ‘shebang’ (first) line of the script.

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Original question

Given that you want mycp "*sh*" aa to do shell expansion on the argument, you’ll probably end up using eval in your script:

eval cp "$@"

However, the use of eval is dangerous; it can lead to unexpected side-effects. The use of "$@" is important; it preserves the number of arguments and spaces in them. Unfortunately, using eval then undoes that, but we can’t have everything — or not easily.

---

For quite a long time (say 1987^* to 1999), I used this script as a cover for cp:

:   "@(#)$Id: cp.sh,v 1.3 1997/06/02 21:45:00 johnl Exp $"
#
#   Alternative copy command

case $# in
0)  /bin/cp     ;;
1)  /bin/cp $1 .    ;;
2)  /bin/cp "$@"    ;;
*)  if [ -d `la "$@"` ]
    then    /bin/cp "$@"
    else    /bin/cp "$@" .
    fi;;
esac

It uses a very simple C program called la (for ‘last argument’) to get the last argument and checks whether the given last argument is a directory. More than 99% of the time, if I typed (by accident) ‘cp /some/where/sh‘ rather than cp /some/where/*sh* ., the second was what I meant, and the script fixed things. I haven’t used it for quite some time; it may have been in the last millennium, but was probably sometime earlier in this one that I gave up using it.

^* Although the version string says ‘1997’, the code is identical to the 1987 version. Version 1.1 and 1.2 were under SCCS and used different SCCS ID strings; the conversion to RCS made them identical. Version 1.3 reinstated the @(#) identifier string used by the SCCS what command to the RCS version handling. So, the script is ancient — 1987, really.