If I have a file with three lines like this
line 1
line 2
curl -H 'Content-Type: application/json' -d '{"user": "joe"}' localhost/api
How can I execute a third line as command in bash?
I tried
$(sed '3q;d' file)
and
`sed '3q;d' file`
but it seems like in both cases the command is only partly executed, I don't get the right result. Of course, calling curl directly works fine.
Unquoted expansion runs string-splitting and globbing, but not other stages of the parsing process. Thus, it doesn't honor quotes, redirections, or other expansions.
This is actually a Good Thing for security reasons -- think about what would happen if you had to worry about the string $(rm -rf ~) being present inside untrusted data that your scripts handle!
That said, if you entirely trust the contents of this file, you can use eval to run it through the entirety of the parsing process:
eval "$(sed '3q;d' file)"
How about running a bash subprocess, with the -c flag?
bash -c "$(sed '3q;d' file)"
From Bash 4 / Bash 3.2(Mac) or higher, you can source the file from a process substitution:
source <(sed '3q;d' file)
or shorter:
. <(sed '3q;d' file)
