Feed source command with a pipe

Previously I used source command like this:

source file_name

But what I’m trying to do is this:

echo something | source

Which doesn’t work.

Answers:

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Method 1

Since source (or .) takes a file as argument, you could try process substitution:

source <(echo something)

Method 2

Your source command requires a file argument. You can get that in some shells with a process substitution, and this is because in the same way the shell replaces…

arg=$(echo hi)

…the echo bit there on the command-line with the subshell’s output, in the case of process substitution it replaces the subshell with a named file – usually /dev/fd/62 or something – some link to a file-descriptor. With a pipe the file descriptor is 0 so…

echo 'echo hi' | . /dev/fd/0

… /dev/stdin or whatever as the case may be should work just fine on any linux system – and many others besides. You can also use here-documents similarly:

. /dev/fd/3 3<<HI
$(echo 'echo hi')
HI

You can verify the way your shell handles process substitution, by the way:

(set -x; readlink <(:))

…which prints (in bash):

+ set +x
+ readlink /dev/fd/63
++ :
pipe:[2212581]

…and so we can see that the shell is doing the substitution and readlink is reading from an an anoymous pipe that it opens on file-descriptor 63.

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