Trying to write a regex in bash - regex

Question

I am new to regex and I am trying to write a regex in a bash script .
I am trying to match line with a regex which has to return the second word in the line .
regex = "commit\s+(.*)"
line = "commit 5456eee"
if [$line =~ $regex]
then
echo $2
else
echo "No match"
fi
When I run this I get the following error:-
man.sh: line 1: regex: command not found
man.sh: line 2: line: command not found
I am new to bash scripting .
Can anyone please help me fix this .
I just want to write a regex to capture the word that follows commit

Answer 1

You don't want a regex, you want parameter expansion/substring extraction:
line="commit 5456eee"
first="${line% *}"
regex="${line#* }"
if [[ $line =~ $regex ]]
then
echo $2
else
echo "No match"
fi
$first == 'commit', $regex == '5456eee'. Bash provides all the tools you need.

Answer 2

If you really only need the second word you could also do it with awk
line = "commit 5456eee"
echo $line | awk '{ print $2 }'
or if you have a file:
cat filename | awk '{ print $2 }'
Even if it's no bash only solution, awk should be present on most linux os's.

Answer 3

You should remove the spaces around the equals sign, otherwise bash thinks you want to execute the regex command using = and "commit\s+(.*)" as arguments.
Then you should remove the spaces also in the if condition and quote the strings:
$ regex="commit\s+(.*)"
$ line="commit 5456eee"
$ if [ "$line"=~"$regex" ]
> then
> echo "Match"
> else
> echo "No match"
> fi
Match

Answer 4

maybe you didn't start your script with the
#!/bin/sh
or
#!/bin/bash
to define the language you're using... ?
It must be your first line.
then be careful, spaces are consistant in bash. In your "if" statement, it should be :
if [ $line =~ $regex ]
check this out and tell us more about the errors you get

Answer 5

if you make this script to a file like test.sh
and execute like that :
test.sh commit aaa bbb ccc
$0 $1 $2 $3 $4
you can get the arguments eassily by $0 $1...

Answer 6

A simple way to get the resulting capture group that was matched (if there is one) is to use BASH_REMATCH, which puts the match results into it's own array:
regex=$"commit (.*)"
line=$"commit 5456eee"
if [[ $line =~ $regex ]]
then
match=${BASH_REMATCH[1]}
echo $match
else
echo "No match"
fi
Since you have only one capture group it will be defined within the array as BASH_REMATCH[1]. In the above example I've assigned the variable $match to the result of BASH_REMATCH[1] which returns:
5456eee