OS: kernel 2.6.x
Shell: POSIX compatible shell
Utilities: BusyBox 1.25
Question: How do you remove the values in $VAR2 from $VAR1 and output the remainder values to $VAR3 ? Each value in the variables is space separated.
Logic:
VAR1="1 2 3 4 5" VAR2="1 3 5" for i in $VAR1 if $i is not found in $VAR2; do append $i to $VAR3 remove trailing space character done Desired Output:
VAR3="2 4" It looks like those are meant to be list of strings which you encode by storing them space separated in a scalar variable (assumes the strings don't contain that space character).
It would make more sense to use variables of type list/array, with shells that support them. For instance, with zsh and its ${varX:|varY} array subtraction operator:
VAR1=(1 2 3 4 5) VAR2=(1 3 5) VAR3=(${VAR1:|VAR2}) (VAR3=("${(@)VAR1:|VAR2}") to preserve empty elements)
Now, if you're limited to POSIX sh that is without array support except for $@, you'll have to be more creative.
The standard command for list intersection and substraction is comm. But the lists have to be provided as a sorted list, newline separated and inside files whose name is passed as arguments (though - can be used for one them to mean stdin).
So here, it becomes awkward to use. If your system supports /dev/fd/<n> special files:
VAR3=$(printf '%s\n' "$VAR1" | tr ' ' '\n' | sort | { printf '%s\n' "$VAR2" | tr ' ' '\n' | sort | comm -23 /dev/fd/3 - } 3<&0 | paste -sd ' ' -) Or:
to_comm() { printf '%s\n' "$@" | tr ' ' '\n' | sort; } from_comm() { paste -sd ' ' -; } VAR3=$(to_comm "$VAR1" | { to_comm "$VAR2" | comm -23 /dev/fd/3 -;} 3<&0 |from_comm) (that also assumes $VAR1 contains at least one element (how would you express a list with one empty elements differently from an empty list, BTW) and that elements don't contain newline characters).
So you might as well implement it by hand. Loop over each element of the first list and look them up in the second list.
In POSIX shells, you could use the split+glob operator:
IFS=' ' # split on space set -o noglob # we don't want the glob part VAR3= sep= for i in $VAR1; do case " $VAR2 " in (*" $i "*) ;; (*) VAR3=$VAR3$sep$i; sep=$IFS;; esac done That can't be used if there may be empty elements (like in VAR1=' 2 3' or VAR1='1 3'). For that it would be better to use a non-whitespace separator (like | below) for which the splitting rules are different:
VAR1='*|foo bar||blah' VAR2='|blah' IFS='|' # split on | set -o noglob # we don't want the glob part VAR3= sep= for i in $VAR1''; do # that $VAR1 split+glob invocation will split the content of $VAR1 # into "*", "foo bar", "", "blah" while with IFS=" ", the empty # element wouldn't have been there as sequences of spaces would # have been seen as a single separator. case "|$VAR2|" in (*"|$i|"*) ;; (*) VAR3=$VAR3$sep$i; sep=$IFS;; esac done The '' in $VAR1'' is to make sure foo| is split into "foo" and "" instead of just "foo" for instance in POSIX shells (most, as that's a POSIX requirement) that treat $IFS as a field terminator instead of separator.
Or you could use awk instead:
export VAR1 VAR2 VAR3=$(awk 'BEGIN{ n = split(ENVIRON["VAR1"], a1, /[ ]/) split(ENVIRON["VAR2"], a2, /[ ]/) for (i in a2) in_a2[a2[i]] for (i = 1; i <= n; i++) if (! (a1[i] in in_a2)) $(++NF) = a1[i] print}') 
comm is a standard/POSIX command. If that's using busybox with comm not enabled, the awk ones should work as long as awk has been enabled. If not, the shell only one should work as long as the ash variant is used for the busybox sh. /dev/fd -> /proc/self/fd symlink (in which case you can use /proc/self/fd instead of /dev/fd in the code above. But in any case, that won't help if you don't have comm. The other solutions should work with the default build of busybox 1.25 VAR3=$(printf "%d\n" $VAR1 $VAR2 | sort | uniq -u | tr '\n' ' ' | sed 's/\s$//) $ echo "$VAR3" 2 4 The main flaw is: it leaves only unique values from the VAR1 variable. That is, if $VAR1 have one value repeated few times, this value doesn't appear in the $VAR3, because it's not unique.
Example:
VAR1="1 2 2 3 4 4 4 5" VAR2="1 3 5" # the resulting VAR3 variable is empty VAR3 = "" # because it is containing only unique values and `2` and `4` repeated few times in the `VAR1`, therefore, they are not unique. # The right result should be VAR3 = "2 2 4 4 4" VAR3=$(printf "%s\n" $VAR2 | awk -v var1="$VAR1" ' {arr2[$1] = 1;} END { size = split(var1, arr1); for(i = 1; i <= size; i++) { if(!arr2[arr1[i]]) printf "%s ", arr1[i]; } }' | sed 's/\s$//') Explanation
printf "%s\n" $VAR2 - converts the $VAR2 to the column - one value per line.awk ... - removes $VAR2 values from $VAR1.
{arr2[$1] = 1;} - puts all VAR2 values (they piped to awk by printf) into the array, where values becomes the array's indexes. The = 1 just mean true - this value exist. This trick give us next behaviour: the first value occurrence create array element, then, if the same value appears again, it goes to the same array index, in other words, the item doesn't changed, when the same value appears few times. Thus, in the end we are having all unique values from the VAR2 variable. If VAR2="one three five", then arr2 will be: arr2[one] = 1, arr2[three] = 1, arr2[five] = 1.END { size = split(var1, arr1); - when input lines ended (VAR2 processing complete), we are splitting the VAR1 into the array - each value goes into the separate item. If VAR1="one two three four five", then we will get the follow array:arr1[1] = one, arr1[2] = two, arr1[3] = three ..., so on. The split function return the size of new, created array.if(!arr2[arr1[i]]) printf "%s ", arr1[i]; - then, iterates through arr1 items and checks, does arr2 have index for this item. For example: i = 1; arr1[1] = "one" then arr2[arr1[i]] is this - arr2[one]. This item exists, don't print it. i = 2; arr1[2] = "two". The arr2[two] doesn't exist, so print it. Thus, we are printing all values from the arr1, which doesn't appear in the arr2.sed 's/\s$//' - removes trailing space.
Pros of this way compared to the first variant:
# It can process strings VAR1="one two three four five" VAR2="one three five" # the resulting VAR3 variable VAR3 = "two four" # It doesn't remove multiple occurrence of one value in the VAR1 VAR1="1 2 2 3 4 4 4 5" VAR2="1 3 5" # the resulting VAR3 variable VAR3 = "2 2 4 4 4" 
sed. I removed previous comments, because they contained wrong information (about newlines and quoting). $( ) can be written on multiple lines. In this case, it starts on the first line VAR3=$( and ends on the last line sed 's/\s$//'). Just copy all code to the command line and press Enter. $VAR1, but all awk command, written on multiple lines do it. I can add comments inside awk code, if you are needed. > echo $VAR1 $VAR2 | tr ' ' '\n' | sort | uniq --unique | tr '\n' ' ' 2 4 
VAR1="1 * 3".