CODEWITHSUNDEEP
regexbash
elethan
elethan

Reputation: 17003

Bash Regex matches on Ubuntu but not on macOS

I have the following bash script:

#!/bin/bash

git_status="$(git status 2>/dev/null)"
branch_pattern="^(# |)On branch ([^${IFS}]*)"
echo $git_status
echo $branch_pattern

if [[ ${git_status} =~ ${branch_pattern} ]]; then
    echo 'hello'
    echo $BASH_REMATCH
fi

Here is the output when I run the script on Ubuntu with bash version 4:

On branch master Initial commit Untracked files: (use "git add <file>..." to include in what will be committed) test.sh nothing added to commit but untracked files present (use "git add" to track)
^(# |)On branch ([^ ]*)
hello
On branch master

However, when I run the same script on macOS with bash version 3, the regex does not match, and nothing inside the if block is executed. The rest of the output is identical. What am I missing? Does my regex need to be formatted differently on macOS/in this version of bash? Is there a flag I am missing?

I have seen similar posts about differences in regex behavior across platforms for e.g., the find command, but I have not yet found a post relevant to my issue.

Upvotes: 0

Views: 300

Answers (2)

Gordon Davisson
Gordon Davisson

Reputation: 126028

It looks to me like there's a bug in the RE engine in the version of bash that macOS comes with (it's rather old -- 3.2.57). It's something to do with the ^(# |) part -- it doesn't seem to match an empty string at the beginning of the string, as it should. But I found a workaround. Apparently the bug doesn't happen if the ^ is inside the parentheses, like this:

branch_pattern="(^# |^)On branch ([^${IFS}]*)"

BTW, you shouldn't use echo $varname to print the contents of a variable. For one thing, it'll do word splitting (converting all runs of whitespace into single spaces) and wildcard expansion on the value, which can be very confusing/misleading. Try something like printf '<<%q>>\n' "$varname" instead. Its output can be a little cryptic if the variable contains weird characters, but at least it'll make it clear that there are weird things in there.

Upvotes: 1

Jebby
Jebby

Reputation: 1955

If you are only trying to get the current git branch name, there is no need for regex. Git already has this built in.

git rev-parse --abbrev-ref HEAD 2>/dev/null

This will print out the current branch name (if any) If you are in a git repository without any commits, it will only return "HEAD"

Upvotes: 1

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