Bash – xargs Loop with Input Variable for Multi-Command Use

bashxargs

I have a text file with various IP addresses.

I would like to cycle through each, and issue a command:

cat ips.txt | xargs -L 1 `ssh me@__IP__ echo "text" > file; reboot;`

But I'm unsure how to pass the xargs value to _IP_.

Could someone explain how this could be accomplished?

Best Answer

You don't need either cat or xargs for this: a simple read in a loop would suffice:

while read -r IP;do
    ssh me@$IP echo "text" > file
    reboot
done < ips.txt

For future reference, what you want for xargs can be achieved with the -I option: you supply a name after -I and any instances of that name in the command itself will be replaced by the arguments xargs receives on the pipe:

... | xargs -L 1 -I myip ssh me@myip 'echo "text">file;reboot'

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Michael's answer is right, and should sort out your problem. Running

cat file | xargs -I % curl http://example.com/persons/%.tar

will download files bob.tar john.tar. sue.tar as expected.

BUT: cat here is useless

rather use:

<file xargs -I % curl http://example.com/persons/%.tar

Bash – How to decode a list of base64-encoded file names

Just add the base64 encoding of newline (Cg==) after each file name and pipe the whole thing to base64 -d:

find . -name "*_*" -printf "%f\n" |
  sed -n 's/_....-..-..\.pdf$/Cg==/p' |
  base64 -d

With your approach, that would have to be something like:

find . -name "*_*" -printf "%f\0" |
  sed -zn 's/_....-..-..\.pdf$//p' |
  xargs -r0 sh -c '
    for i do
      echo "$i" | base64 -d
    done' sh

as you need a shell to create those pipelines. But that would mean running several commands per file which would be quite inefficient.

Best Answer

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