用bash中的确切值替换变量（不扩展）

Question

I have written a script as follows:

#!/bin/bash

opt1='-vvaumrhhhsq --info=name1 --delete --modify-window=2 --safe-links'
opt2="--progress --exclude-from=$HOME/exrsync"
opt3='--exclude-from="$excl" --log-file="$logfile"'

src="$HOME"
dest="/My Backup/home/"    
excl="$HOME/exrsync-gh"
logfile="rsync_home.log"

rm -f "$logfile"
rsync ${opt1} ${opt2} ${opt3} "$src" "$dest"

Based on bash -x myscript.sh output:
opt1 varibale has nothing to be expanded, ie:

 + opt1='-vvaumrhhhsq --info=name1 --delete --modify-window=2 --safe-links'

opt2 is expanded on the line it is defined, ie:

+ opt2='--progress --exclude-from=/home/username/exrsync'

and opt3 is not expanded in the line it is defined, ie:

+ opt3='--exclude-from="$excl" --log-file="$logfile"'

But in the last command of the script, opt1 and opt2 are replaced by their values without '' , but each part of opt3 is putted inside single quotes, ie:

+ rsync -vvaumrhhhsq --info=name1 --delete --modify-window=2 --safe-links --progress --exclude-from=/home/me/backup/rsync/exrsync '--exclude-from="$excl"' '--log-file="$logfile"' /home/me '/My Backup/home/'

Obviously above command will return an error:

rsync: failed to open exclude file "$excl": No such file or directory (2)
rsync error: error in file IO (code 11) at exclude.c(1179) [client=3.1.0]

I need that opt3 to be raplaced such as opt1 is replaced. Thus the last command will be as follows:

+ rsync -vvaumrhhhsq --info=name1 --delete --modify-window=2 --safe-links --progress --exclude-from=/home/me/backup/rsync/exrsync --exclude-from=/home/me/exrsync-gh --log-file=rsync_home.log /home/me '/My Backup/home/'

Note:
One solution is to put opt3 definition after excl and logfile definitions, so it coulde be expnded in the line it is defines. But I do not want to do that, because in the future I want to add some loops to above script and in this way I have to re-define opt3 every time excl or logfile change.

Answer 1

You should be using arrays to store program arguments. You also need to define logfile and excl before you use them to set the value of opt3 .

#!/bin/bash

src="$HOME"
dest="/My Backup/home/"    
excl="$HOME/exrsync-gh"
logfile="rsync_home.log"

opt1=(-vvaumrhhhsq --info=name1 --delete --modify-window=2 --safe-links)
opt2=(--progress --exclude-from=$HOME/exrsync)
opt3=(--exclude-from="$excl" --log-file="$logfile")



rm -f "$logfile"
rsync "${opt1[@]}" "${opt2[@]}" "${opt3[@]}" "$src" "$dest"

---

One thing you can do is wrap your rsync command in a function that will take two arguments, the value of excl and the value of logfile .

syncer () {
    excl=$1
    logfile=$2
    shift 2
    options=( --vvaumrhhhsq
              --info=name1
              --delete
              # etc
    )
    rsync "${options[@]}" --exclude-from="$excl" --log-file="$logfile" "$@"
}

syncer "$excl" "$logfile" "$src" "$dest"