Issue with Expression in For Loop - Bash

Question

I am trying to loop through a list of servers and rather than manually enter each one in a text file, I wanted to use an expression.

Example:

[user@server001 ~]$ for i in server{001..010} ; do echo $i ; done
server001
server002
server003
server004
server005
server006
server007
server008
server009
server010

That Produces the desired result. However when I put server{001..010} into a .txt file and try to do the same thing, it doesn't work:

[user@server001 ~]$ cat server_test2.txt
server{001..010}
[user@server001 ~]$ for i in `cat server_test2.txt` ; do echo $i ; done
server{001..010}

As you can see it doesn't actually handle the expression the way I'd like it to.

Any ideas how I can extrapolate from a txt file with multiple lines of servers using the expression method? {001..010}

Order of operations. The output from a command substitution is not brace expanded. — Etan Reisner, Feb 24 '15 at 19:29
Please see http://stackoverflow.com/questions/9337489/bash-curly-brace-expansion-with-variable-for-mkdir — chrisinmtown, Feb 24 '15 at 19:33
The order of expansions is listed here: https://www.gnu.org/software/bash/manual/bashref.html#Shell-Expansions — glenn jackman, Feb 24 '15 at 19:36

score 0 · Accepted Answer · answered Feb 24 '15 at 19:35

0

you could use eval; like this:

list=$(cat server_test2.txt)
CMD="for i in $list ; do echo \$i; done"
eval $CMD

answered Feb 24 '15 at 19:35

Chris Maes

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That worked great, thanks! I'll have to read up on eval to understand why ;) – Nick Greenfield Feb 24 '15 at 19:46
`man eval` should help you on your way: it "evaluates" the string as a command. As noted in related questions; it is a "dangerous" command though – Chris Maes Feb 24 '15 at 19:58

Issue with Expression in For Loop - Bash

1 Answers1