Bash variable returns "command not found" in OSX Terminal

Question

I tried using some variables to rename a few files, but it failed miserably. I've tried different ways of getting it to work, but to no avail. As far as I understand the documentation, this is the correct way of doing things - however now I'm stumped...

Here's the code (as written in the file rename_prefix.sh):

 #!/bin/sh
 NEWPREF="LALA"
 OLDPREF="LULU"
 for f in $OLDPREF*; do mv $f $(echo $f | sed 's/^$OLDPREF/$NEWPREF/g'); done

Here's the error message:

 usage: mv [-f | -i | -n] [-v] source target
   mv [-f | -i | -n] [-v] source ... directory

Initially I thought the problem lay in using variables with what I assume are the regular expressions, but as can be seen from the error messages, the problem lies where the variables are first declared.

What's going on here?

variables are not interpreted in single quotes '. Try using double quotes " in the sed command e.g. sed "s/^$OLDPREF/$NEWPREF/g" or something similar — user000001
– user000001, Commented Mar 22, 2013 at 9:01
Are you certain there's no spaces, e.g. NEWPREF ="LALA" in your script ? — nos
– nos, Commented Mar 22, 2013 at 9:03
Oh man... bad. Almost definitely should be quoting "$OLDPREF" in the glob, and definitely definitely shouldn't be recycling it for use as a regex. Use parameter expansion for string manipulation of shell variables if at all possible. Lots of quoting issues here. — ormaaj
– ormaaj, Commented Mar 22, 2013 at 9:06
No spaces double-check: Affirmative! I am certain. Single quoting double quotes, and double quoting single quotes didn't work. Double quoting variable in the glob didn't work. Error message unchanged, suggesting the problem is the variable declaration and not the glob/regex line. — Kebman
– Kebman, Commented Mar 22, 2013 at 9:13
You can't have any quotes around globbing characters if you want filename expansion, single or double. You almost certainly have some whitespace between variable name and the = to get those error messages. Try: od -xc rename_prefix.sh to see "hidden" characters, like \r. — cdarke
– cdarke, Commented Mar 22, 2013 at 9:22

Jens · Accepted Answer · 2013-03-22 10:51:12Z

4

This can be done entirely in the shell, which also avoids the possible problem of escaping metacharacters for the sed substitution patterns. It is also blazingly fast because it saves two forks per file renamed.

NEWPREF="LALA"
OLDPREF="LULU"
for f in "$OLDPREF"*; do
   mv "$f" "$NEWPREF${f#$OLDPREF}"
done

If you want to learn more about removing suffixes and prefixes from shell variable values, read up the POSIX spec on parameter expansion (which all of zsh, ksh, mksh, and bash support).

PS: The only way you can get an error like rename_prefix.sh: line 2: NEWPREF: command not found is if you had whitespace after NEWPREF and before the =. It looks very much like your program as posted is not exactly the program you ran. Did you type it instead of cut'n'paste it?

edited Mar 22, 2013 at 10:51

answered Mar 22, 2013 at 9:24

Jens

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7 Comments

Kebman Over a year ago

Error: mv: rename ABY to PPU: No such file or directory

Jens Over a year ago

What does echo $OLDPREF* expand to?

ormaaj Over a year ago

Whether you should use something like this answer or mine essentially depends upon whether OLDPREF is intended to be a pattern. If no, this has quoting issues. If yes, you should set IFS= in order to deal with whitespace characters, however it's generally not a good idea to put patterns into variables.

Jens Over a year ago

The poster explicitly gave the old and new prefixes as strings without metacharacters. Of course it is always good to state assumptions.

ormaaj Over a year ago

as you mentioned, it's pretty much the only way this can fail unless there were no glob matches. edit +1 anyway, it's a right answer for some definition of right. :)

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Jens · Accepted Answer · 2013-03-22 13:20:34Z

0

Alright so assuming you don't require POSIX, and guessing about certain other details, here's the same thing with general corrections applied.

#!/bin/bash
newpref=LALA
oldpref=LULU

shopt -s nullglob

for f in "$oldperf"*; do
    mv -- "$f" "${f/#"$oldpref"/$newpref}"
done

or POSIX

#!/bin/sh
newpref=LALA
oldpref=LULU

for f in "$oldpref"*; do
    [ -e "$f" ] || break
    mv -- "$f" "${newpref}${f#"$oldpref"}"
done

edited Mar 22, 2013 at 13:20

Jens

73.3k16 gold badges134 silver badges186 bronze badges

answered Mar 22, 2013 at 9:25

ormaaj

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8 Comments

Jens Over a year ago

What about keeping the case of variables consistent? oldpref != OLDPREF. And it is pref, not perf. This script certainly wasn't tested.

ormaaj Over a year ago

@Jens You should conventionally avoid all-caps variable names for purely internal purposes, as they may cause conflicts and can be mistaken for environment variables.

Jens Over a year ago

You misunderstand: you are using BOTH. One of them uninitialized. This can't work at all. And you also use both the proper spelling and misspelling (perf). Why didn't you bother to test run your script, which would immediately have shown all those errors?

ormaaj Over a year ago

@Jens I don't see this, I missed a few previously and edited.

ormaaj Over a year ago

@Jens Ah you mean s/pref/perf. I see. Thanks.

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