Pipe output to environment variable export command

Question

I'm trying to set a git hash value into an environment variable, i thought it would be as simple as doing this:

git log --oneline -1 | export GIT_HASH=$1

But the $1 doesn't contain anything. What am I doing wrong?

Don Cruickshank · Accepted Answer · 2016-10-25T16:35:27.670

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$1 is used to access the first argument in a script or a function. It is not used to access output from an earlier command in a pipeline.

You can use command substitution to get the output of the git command into an environment variable like this:

export GIT_HASH=`git log --oneline -1`

However...

This answer is specially in response to the question regarding the Bourne Shell and it is the most widely supported. Your shell (e.g. GNU Bash) will most likely support the $() syntax and so you should also consider Michael Rush's answer.

But some shells, like tcsh, do not support the $() syntax and so if you're writing a shell script to be as bulletproof as possible for the greatest number of systems then you should use the `` syntax despite the limitations.

edited Oct 25 '16 at 16:35

answered Mar 09 '14 at 20:48

Don Cruickshank

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For those who care the `export EMR_CLUSTER_ID_HELPER=\`cat /mnt/var/lib/info/job-flow.json | jq -r ".jobFlowId"\`` command works on Amazon EC2-Instance. I just tried it out to use for myself to so that I could put the EMR Cluster ID into an environment variable. So use the `` they work well. Thanks Don Cruickshank – Kyle Bridenstine May 15 '18 at 00:36
In case of `git log --oneline -1` failure, `export GIT_HASH=...` **will not fail**. In some cases it may lead to bugs hard to spot (i.e. CI/CD pipeline execution). I would suggest following modification `GIT_HASH=$(git log --oneline -1) && export GIT_HASH=$GIT_HASH` – Paweł Dulęba Feb 24 '20 at 11:57

score 41 · Answer 2 · edited May 23 '17 at 12:18

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Or, you can also do it using $(). (see What is the benefit of using $() instead of backticks shell scripts?)

For example:

export FOO_BACKWARDS=$(echo 'foo' | rev)

edited May 23 '17 at 12:18

Community

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answered May 09 '16 at 21:14

Michael Rush

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score 2 · Answer 3 · answered Oct 25 '19 at 09:51

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You can use an external file as a temporary variable:

TMPFILE=/var/tmp/mark-unsworth-bashvar-1
git log --oneline -1  >$TMPFILE; export GIT_HASH=$(cat $TMPFILE); rm $TMPFILE
echo GIT_HASH is $GIT_HASH

answered Oct 25 '19 at 09:51

Sohail Si

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Pipe output to environment variable export command

3 Answers3