How do I call a script with a wildcard pattern and two more arguments?

Question

I have this code to rename a bunch of files:

#!/bin/bash
for file in $1
    do
        mv -i "${file}" "${file/pattern/replacement}"
    done

How do I replace "pattern" and "replacement" with $2 and $3?

This code does not work:

#!/bin/bash
for file in $1
    do
        mv -i "${file}" "${file/$2/$3}"
    done

I'm trying to rename using the following 3 arguments: file_*.jpg jpg bak (the result should be renaming all *.jpg files to *.bak files). But all it does is: mv -i file_01.jpg file_01.jpg (thus not renaming anything, since both mv arguments are identical, plus it stops at the first file, even when there are more *.jpg files). If I manually type jpg and bak into the bash script instead of $2 and $3 then it DOES work.

Solution

You call your script with

./script file_*.jpg jpg bak

But * gets expanded before it is passed to the script. Assuming you have the files file_1.jpg, file_2.jpg and file_3.jpg in your folder, this is what is invoked:

./script file_1.jpg file_2.jpg file_3.jpg jpg bak

which means that ${1} = file_1.jpg, ${2} = file_2.jpg and ${3} = file_3.jpg.

It might be better if you write your script such, that (in your example): ${1} = jpg and ${2} = bak. Then you can store those variables in your script, invoke shift 2 to get rid of them, and loop over all positional arguments simply by using

for file; do
    # do something
done

Comments

[Ipor Sircer]

It works for me.

[pfnuesel]

How do you invoke that script?

[pfnuesel]

Maybe add #!/usr/bin/env bash on top of the script, to make sure bash is invoked.

[Арсений Черенков]

It looks like you are rewriting rename command ...

[OMA]

@Archemar: What rename command? Excuse my ignorance, but I don't know any rename command other than "mv"

[Арсений Черенков]

see man rename

[OMA]

That command is not available for me. That's why I asked.

[Stéphane Chazelas]

As written, the script would work if called as ./script 'file_*.jpg' jpg bak as $1 is unquoted, so subject to split+glob, so that file_*.jpg would be expanded at that point. Your advice of having $1=pat, $2=ret and the rest the list of files is certainly best though (1- to avoid having to quote the pattern, 2- to avoid confusing users of other shells with different globs than bash, 3- to allow patterns like my file*...)

[Stéphane Chazelas]

consider using getopts to process your options. For instance, had you used getopts, you would have been able to do myscript -- -p -q files to replace -p with -q, and -ppp would have meant the same as -p.

[Stéphane Chazelas]

Your use of needle, haystack and wildcard words is confusing here.

[Stéphane Chazelas]

Note that if your boolean variables are made to contain only true or false, you can just do if "$found" instead of if [ "$found" = true ].

[Stéphane Chazelas]

Note that [ -f "$file" ] is not for file existence, but that the file exists and is a regular file (or symlink to regular file). That would exclude all other types of file like fifo, device, directory...

[OMA]

Thanks a lot for reviewing my code and for all your comments, Stéphane! You're really helpful! I've implemented most of your suggestions, except getopts (I have to learn more about it) and if [ "$found" ], because that results in true when $found contains "false" (it's a string after all; I used strings since booleans don't exist in Bash). Also I don't mind the if [ -f "$file" ] checking only for regular files. It's all I need for now.

[OMA]

BTW, it seems I'm reinventing the wheel here since there is an actual "rename" command I didn't know about the existence of, but it's not available on my machine, so my script will do. Plus, it's a nice exercise in Bash scripting :)

[Stéphane Chazelas]

yes, rename (both util-linux, perl's and now separate perl script with more extensions) and also mmv and zsh's zmv...

[Stéphane Chazelas]

Note that I said if "$found", not if [ "$found" ], as in run the command stored in $found (false and true being builtin bash commands), not the [ command with the content of $found as argument.

[OMA]

Ah, I see. That's another intricacy I didn't know about :). About "mmv" and "zmv", those aren't available here, either

[Stéphane Chazelas]

zmv is a function shipped with zsh, so you can use all the expansion operators and glob operators of zsh (use autoload zmv from within zsh to enable it). You can search this site for zmv to see hundreds of examples.