[SOLVED] Bash script: confusing concatenation of explicit string and variable

itayshom · 11-21-2014, 07:25 AM

Hello all,

I'm trying to use rsync to back up my data with the following script:

Code:

#!/bin/bash

TARGET="/var/run/media/itayshom/160 GB Volume"

rsync -a /home/itayshom "'${TARGET}'"

However, I get the following error:

Code:

rsync: mkdir "/home/itayshom/'/var/run/media/itayshom/160 GB Volume'" failed: No such file or directory (2)
rsync error: error in file IO (code 11) at main.c(656) [Receiver=3.1.1]

For some reason, my home directory string gets concatenated to the next argument (even though there's a space).
If I just echo the command, I get the correct answer:

Code:

rsync -a /home/itayshom '/var/run/media/itayshom/160 GB Volume'

and it executes perfectly if entered by hand!

I know bash quotation can be tricky but I couldn't find an answer to this one.

Does anyone know what the problem is?

Thanks,
Itay.

rknichols · 11-21-2014, 09:13 AM

It is not concatenating the strings. It's just that your CWD happens to be the same as that source argument, and rsync is trying to create a directory "$CWD/'/var/run/media/itayshom/160 GB Volume'".

The real problem is that for a local destination you don't want that extra level of quoting to protect the spaces in that argument since there is no remote shell involved. Since the path is seen as beginning with a quote mark and not "/", it is taken as relative to the CWD rather than absolute. Any of these should work:

Code:

rsync -a /home/itayshom "${TARGET}"                           # Eliminate the extra quoting
rsync -a /home/itayshom localhost:"'${TARGET}'"               # Make it a "remote" destination
rsync -a --protect-args /home/itayshom localhost:"${TARGET}"  # Protect the arguments against word splitting
rsync -a --protect-args /home/itayshom "${TARGET}"            #    and the same syntax works for both local and remote

itayshom · 11-21-2014, 10:14 AM

Thanks rknichols! It works.

I used the first example, even though I don't completely understand why I can give up the quotes.

I have a follow-up question. Now I want to execute the command

Code:

rsync -a --exclude='.cache/' --exclude='.thumbnails/'  /home/itayshom '/var/run/media/itayshom/160 GB Volume'

So as to exclude some directories from backup. I want to keep the quotes because in the future I might have some directories with spaces in their names. For this I wrote the script:

Code:

#!/bin/bash

TARGET="/var/run/media/itayshom/160 GB Volume"

EXCLUSIONS=(
  ".cache"
  ".thumbnails"
)

for i in "${EXCLUSIONS[@]}"; do EXCLUDE+="--exclude='$i/' "; done   # note the quotes around $i/

rsync -a "${EXCLUDE}" /home/itayshom "${TARGET}"

Again, when echoing the last line it shows up exactly as I want it (this is very annoying). However running the script, rsync misinterprets the --exclude arguments and copies the contents of .cache etc.
This happens even if I remove the single quotes, e.g. --exclude=.cache/ so I hope this question is not just repeating my previous one.

How can I make bash to tell rsync the right directories to exclude?

Any help would be much appreciated
Itay.

rknichols · 11-21-2014, 10:58 AM

Quote:

Originally Posted by itayshom

Code:

rsync -a "${EXCLUDE}" /home/itayshom "${TARGET}"

You can't have those quotes around ${EXCLUDE}. That causes the whole string to be passed as one argument, so rsync would try to exclude a file whose name was the entire string following that first "=" character, as though you had entered:

Code:

--exclude=".cache --exclude=.thumbnails"

And, you indeed don't want those single quotes around the individual file names. They will be taken literally, as part of the name.

It gets messy trying to build up argument strings that way. Using an array is much more straightforward:

Code:

EXCLUSIONS=(
  ".cache"
  ".thumbnails"
)
N=0
for i in "${EXCLUSIONS[@]}"; do EXCLUDE[N++]="--exclude=$i/"; done

rsync -a "${EXCLUDE[@]}" /home/itayshom "${TARGET}"

I believe this all works even when some of the EXCLUSIONS names contain embedded spaces.

itayshom · 11-21-2014, 04:28 PM

Thanks! That solved it.

Itay.