Trying to write a regex in bash

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

Note: the =~ operator is only valid with double bracket syntax [[ .. ]] — David C. Rankin
– David C. Rankin, Commented Apr 15, 2015 at 9:35
Your seeing command not found because you have a space between the variable name and the value. Example: regex = "commit\s+(.*)" should become regex="commit\s+(.*)". See answers below. — Tim Rijavec
– Tim Rijavec, Commented Apr 15, 2015 at 9:54

David C. Rankin · Accepted Answer · 2015-04-15 09:39:41Z

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.

edited Apr 15, 2015 at 9:39

answered Apr 15, 2015 at 9:33

David C. Rankin

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Comments

cb0 · Accepted Answer · 2015-04-15 09:45:39Z

1

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.

answered Apr 15, 2015 at 9:45

cb0

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2 Comments

Newbie Over a year ago

How do i copy the output into a variable?

cb0 Over a year ago

You could redirect it with another pipe, output it to a file using cat filename | awk '{ print $2 }' > filename or just do output=$(cat filename | awk '{ print $2 }') to capture output inside the $output var.

enrico.bacis · Accepted Answer · 2015-04-15 09:36:35Z

0

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

edited Apr 15, 2015 at 9:36

answered Apr 15, 2015 at 9:30

enrico.bacis

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2 Comments

David C. Rankin Over a year ago

There is no =~ operator for [ .. ], only [[ .. ]]

Tim Rijavec Over a year ago

You can use =~ like that as long you don't have spaces around the operator.

Random · Accepted Answer · 2015-04-15 09:34:34Z

0

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

answered Apr 15, 2015 at 9:34

Random

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ohohyeah · Accepted Answer · 2015-04-15 09:39:44Z

0

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...

answered Apr 15, 2015 at 9:39

ohohyeah

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Comments

l'L'l · Accepted Answer · 2015-04-15 10:13:01Z

0

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

answered Apr 15, 2015 at 10:13

l'L'l

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