Looping through variables which is an output of another command
Hello I am learning Scripting here. I am trying to write a simple script using the ‘for’ loop.
I have hundreds of folders in a folder called user.
if i run this command i get a list of folders that i need to move to another folder
cat failed | awk -F ":" '/FAILED/ {print $1}' | uniq
i.e folders under users that have failed a task have to be moved to users/failed/failedusers
what i am currently doing is i am creating a new file first using
cat failed | awk -F ":" '/FAILED/ {print $1}' | uniq > failedusers
and then i move the folders using the following command
while read line; do cp -r users/$line users/failed; done < failedusers
My question here is can i do the same using just the for command instead of writing the output to another file and using the while read command to get it done?
for example somehow assign a value to a variable in a loop like
faileduser=`cat failed | awk -F ":" '/FAILED/ {print $1}' | uniq`
and then write something like
mv users/$faileduser user/failed/$faileduser
i am getting all kinds of errors when i am trying to write something like above.
thanks
With GNU xargs and a shell with support for ksh-style process substitution, you can do:
xargs -rd 'n' -I USER -a <(awk -F : '/FAILED/ {print $1}' failed | sort -u
) cp -r users/USER user/failed/USER
With zsh, you could do:
faileduser=( ${(f)"$(awk -F : '/FAILED/ {print $1}' failed | sort -u)"} )
autoload zargs
zargs -rI USER -- $faileduser -- cp -r users/USER user/failed/USER
Assuming you want to copy USER to user/failed/USER, that is, copy it into user/failed, you could also do (still with zsh):
(( $#faileduser )) && cp -r users/$^faileduser user/failed/
With the bash shell, you could do something similar with:
readarray -t faileduser < <(awk -F : '/FAILED/ {print $1}' failed | sort -u)
(( ${#faileduser[@]} )) &&
cp -r "${faileduser[@]/#/user/}" user/failed/
Or get awk to prepend the user/ to all the user names:
readarray -t faileduser < <(awk -F : '/FAILED/ {print "user/"$1}' failed | sort -u)
(( ${#faileduser[@]} )) &&
cp -r "${faileduser[@]}" user/failed/
With a for loop, with Korn-like shells (including bash, and would also work with zsh) the syntax would be:
for user in "${faileduser[@]}"; do
cp -r "user/$user" "user/failed/$user"
done
Which in zsh could be shortened to:
for user ($faileduser) cp -r user/$user user/failed/$user
With:
faileduser=`cat failed | awk -F ":" '/FAILED/ {print $1}' | uniq`
(`...` being the archaic and deprecated form of command substitution. Use $(...) instead).
You’re storing awk‘s output in a scalar, not array variable.
In zsh, you can split it on newline with the f parameter expansion flag like we do directly above on the command substitution:
array=( ${(f)faileduser} )
In bash (or ksh), you could use the split+glob operator after having disabled glob and tuned split:
set -o noglob
IFS=$'n'
array=( $faileduser )
(yes, in bash, leaving a parameter expansion unquoted invokes an implicit split+glob operator (!), a misfeature inherited from the Bourne shell, fixed in zsh and most modern non-Bourne-like shells).