How to get the parent of a specific commit in Git

I have a commit number. I would like to get the previous commit number (parent). I need commits from the current branch.

git log --pretty=%P -n 1 "$commit_from"

To get Parent Commit

git cat-file -p commit_id

tree tree_id
parent parent_commit_id
[parent other_parent_commit_id] # present only in case of merge commits
author xxx <[email protected]> 1513768542 +0530
committer xxx <[email protected]> 1513768542 +0530 

If ${SHA} is the commit you know and you want its parent (assuming it's not a merge commit and has only one parent):

git rev-parse ${SHA}^

You can use git rev-parse for this.

# Output hash of the first parent
git rev-parse $commit^

# Nth parent
git rev-parse $commit^N

# All parents
git rev-parse $commit^@

These constructs are explained in git help rev-parse:

 <rev>^, e.g. HEAD^, v1.5.1^0
     A suffix ^ to a revision parameter means the first
     parent of that commit object.  ^<n> means the <n>th
     parent (i.e.  <rev>^ is equivalent to <rev>^1). As a
     special rule, <rev>^0 means the commit itself and is
     used when <rev> is the object name of a tag object that
     refers to a commit object.

 ...

 <rev>^@, e.g. HEAD^@
     A suffix ^ followed by an at sign is the same as listing
     all parents of <rev> (meaning, include anything
     reachable from its parents, but not the commit itself).