Using source to include part of a file in a bash script

Question

I've a bash script that need to use some variables included in a separate file.

Normally, for including the entire file I would use source otherfile.sh in the main script. In this case I need to use just a portion of this file. I can't use (include) the rest of the variables included in the rest of the file.

To filter the content of the config file (let's say just as example from the tag "# start" to "# end") I use awk, but I can't redirect the output to the soruce command.

Below my code:

awk ' /'"# start"'/ {flag=1;next} /'"# end"'/{flag=0} flag { print }' config.sh

Do you know any way to redirect the output of this command into source? Is there any other way to include the output in my bash script at run-time?

By the way, I wouldn't like to create temporaty files (it seems me too dirty...)..and I've tried something found on this site, but for some reasons it doesn't work. Below there's the solution I've found.

awk ' /'"# start"'/ {flag=1;next} /'"# end"'/{flag=0} flag { print }' config.sh | source /dev/stdin

Thank you,

Luca

chepner · Accepted Answer · 2014-03-05 13:04:06Z

5

source can read from a process substitution in bash:

source <( awk ' ... ' config.sh )

sed allows a simpler way to get the subset of lines:

sed -n '/#start/,/#end/p' config.sh

UPDATE: It appears that this may only work in bash 4 or later.

edited Mar 5, 2014 at 13:04

answered Mar 4, 2014 at 22:02

chepner

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2 Comments

lukedj Over a year ago

Hi Chepner, I tried to execute the code above but using 'source <(sed -n '/#start/,/#end/p' config.sh)' returns line 7: source/dev/fd/63: No such file or directory. Using 'source<$(sed -n '/#start/,/#end/p' config.sh)' says line 7: $(sed -n '/#start/,/#end/p' config.sh): ambiguous redirect. I report the correct answer given by a friend today below. Thank you anyway!

chepner Over a year ago

Strange. I tried source <(echo foo=bar), which should set the value of foo to "bar" in the current shell. It works as expected in bash 4.1 and above. It does fail in bash 3.2, although I don't see any error message as you report with the first attempt. The second attempt should fail, since you are trying to use the output of sed as a file name, which is syntactically incorrect, I think.

lukedj · Accepted Answer · 2014-03-05 09:45:23Z

2

A correct way of doing it provided by a friend today. Here's the code:

source /dev/stdin <<EOF
$(awk ' /'"# 10.216.33.133 - start"'/ {flag=1;next} /'"# 10.216.33.133 - end"'/{flag=0} flag { print }' testbed.sh)
EOF

Working perfectly...thanks Andrea! :) (and of course everyone tried to answer)

answered Mar 5, 2014 at 9:45

lukedj

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