Grep Context

27th June 2020 - 3 minutes read time

Grep is a really powerful tool for finding things in files. I often use it to scan for plugins in the Drupal codebase or to scan through a CSV or log file for data.

For example, to scan for user centric ViewsFilter plugins in the Drupal core directory use this command (assuming you are relative to the core directory).

grep "@ViewsFilter(\"user" -r core

The -r flag here recursively scans the 'core' directory. This command returns the following output.

core/modules/user/src/Plugin/views/filter/Roles.php: * @ViewsFilter("user_roles")
core/modules/user/src/Plugin/views/filter/Permissions.php: * @ViewsFilter("user_permissions")
core/modules/user/src/Plugin/views/filter/Current.php: * @ViewsFilter("user_current")
core/modules/user/src/Plugin/views/filter/Name.php: * @ViewsFilter("user_name")

One thing I do when looking at log files is to look at the context surrounding the returned strings from grep. This is the lines above or below the matched lines. Grep has a couple of built in flags that allow this.

Here is an excerpt from the documentation.

   Context Line Control
       -A NUM, --after-context=NUM
              Print NUM  lines  of  trailing  context  after  matching  lines.
              Places   a  line  containing  a  group  separator  (--)  between
              contiguous groups of matches.  With the  -o  or  --only-matching
              option, this has no effect and a warning is given.
 
       -B NUM, --before-context=NUM
              Print  NUM  lines  of  leading  context  before  matching lines.
              Places  a  line  containing  a  group  separator  (--)   between
              contiguous  groups  of  matches.  With the -o or --only-matching
              option, this has no effect and a warning is given.
 
       -C NUM, -NUM, --context=NUM
              Print NUM lines of output context.  Places a line  containing  a
              group separator (--) between contiguous groups of matches.  With
              the -o or --only-matching option,  this  has  no  effect  and  a
              warning is given.

Carrying on from the example above, if you want to look at the context 3 lines after your match you would use the -A flag like this.

grep "@ViewsFilter(\"user" -r core -A 3

If you want to look at the context 3 lines before your match you would use the -B flag like this.

grep "@ViewsFilter(\"user" -r core -B 3

If you want to look at the context 3 lines before and 3 lines after your match use the -C flag like this.

grep "@ViewsFilter(\"user" -r core -C 3

The easy way to remember this is the -A flag if for AFTER, the -B flag is for BEFORE, and in typical Unix humour, the combination of the two is the -C flag.

grep

command line

Add new comment

Keychron K2 Wireless Mechanical Keyboard: A Review

I (like a lot of other people) recently started to work at home a lot more, and with a permanent desk setup at home I wanted a decent keyboard to work with. My work machine is a MacBook Pro 2018 and I dislike the keyboard quite a lot. It feels 'poppy', has some interesting key placements (the up and down arrows in particular), has no escape key or function keys at all.

Wrap Around Increments

Something I've been writing long hand for a number of years is wrap around increments. This is essentially adding to a value that has an upper limit, and wrapping back to 0 when that max value is reached. This can be done with an if statement.

Creating A Chatbot Agent With Dialogflow And Kommunicate

Having a chat feature on your website (commonly called 'live chat') is useful when helping your users overcome any difficulties they are having. You can pop up a little chat window in the page and ask if they need any help finding what they need. This can be especially useful on large commerce sites where users might get stuck looking for things.

The addition of a chatbot also allows you to automatically answer some of more common questions. For example, if a user asks where they can find the delivery and returns policy then a chatbot can automatically respond with a response. These rules can get more complicated, but it depends on what you instruct the bot to answer to.

Overwriting Command Line Output With PHP

The other day I was trying to print some output to the command line and then overwrite the output afterwards. It turns out that there are a couple of ways to do this so I thought I would detail a few of them here.

By far the simplest way of doing this is to run the "clear" command, which we can run via the system() function in PHP. This will clear the output of the command line ready for you to print out whatever you need. The downside to this is that the entire terminal window is cleared. Another downside is that once the output is complete scrolling up will reveal the output that was cleared out.

Adventures In FizzBuzz

Tests for programmers in an interview process are not uncommon. For the last couple of years I have asked a quick pre-interview question to junior developers to see what sort of stuff they come up with.

As I don't want to set any developer a task that will take longer than absolutely needed I opted to set a very simple task for them. Commonly known as "FizzBuzz", this task is as follows.

"Write a program that prints the numbers from 1 to 100. But for multiples of three print "Fizz" instead of the number and for the multiples of five print "Buzz". For numbers which are multiples of both three and five print "FizzBuzz"."

The expected output for this would be something like this.