linux

Unix/Linux: Find all files that contain multiple strings/patterns alvin September 5, 2019 - 8:36am

When using Unix or Linux, if you ever need to find all files that contain multiple strings/patterns, — such as finding all Scala files that contain 'try', 'catch', and 'finally' — this find/awk command seems to do the trick:

find . -type f -name *scala -exec awk 'BEGIN {RS=""; FS="\n"} /try/ && /catch/ && /finally/ {print FILENAME}' {} \;

As shown in the image below, all of the matching filenames are printed out. As Monk says, you’ll thank me later. :)

(I should mention that I got part of the solution from this gnu.org page.)

Linux: Recursive file searching with grep -r (like grep + find) alvin July 23, 2019 - 7:46pm

Linux grep FAQ: How can I perform a recursive search with the grep command in Linux?

Solution: find + grep

For years I always used variations of the following Linux find and grep commands to recursively search subdirectories for files that match a grep pattern:

find . -type f -exec grep -l 'alvin' {} \;

This command can be read as, “Search all files in all subdirectories of the current directory for the string ‘alvin’, and print the filenames that contain this pattern.” It’s an extremely powerful approach for recursively searching files in all subdirectories that match the pattern I specify.

The Unix/Linux `htop` command alvin July 22, 2019 - 3:07pm

One new thing I learned in the last week is the `htop` command. It’s a nicely-improved version of the standard top command. This image provides some hints as to its features. If you have a Mac, you can install it with Homebrew.

How to use the Linux ‘scp’ command without a password to make remote backups alvin July 17, 2019 - 5:19pm

Summary: How to create a public and private key pair to use ssh and scp without using a password, which lets you automate a remote server backup process.

Over the last two years I've ended up creating a large collection of websites and web applications on a variety of Linux servers that are hosted with different companies like GoDaddy and A2 Hosting. I recently embarked on a mission to automate the backup processes for all these sites, and as a result of this effort, I thought I'd share what I've learned here.

Linux crontab examples (every X minutes or hours)

Table of Contents1 - Linux crontab: How to run a command every minute2 - Descriptions of the crontab date/time fields3 - Run a crontab command every hour4 - Run a crontab entry every day5 - Run a crontab entry every 5 minutes6 - Unix and Linux “crontab every” summary7 - Unix and Linux crontab reference information

Linux crontab FAQ: How do I schedule Unix or Linux crontab jobs to run at intervals, like “Every five minutes,” “Every ten minutes,” “Every half hour,” and so on?

Solution: I’ve posted other Unix/Linux crontab tutorials here before (How to edit your Linux crontab file, Example Linux crontab file format), but I’ve never included a tutorial that covers the “every” options, so here are some examples to demonstrate this crontab syntax.

A big collection of Unix/Linux `find` command examples

Linux/Unix FAQ: Can you share some Linux find command examples?

Sure. The Unix/Linux find command is very powerful. It can search the entire filesystem to find files and directories according to the search criteria you specify. Besides using the find command to locate files, you can also execute other Linux commands (grep, mv, rm, etc.) on the files and directories you find, which makes find extremely powerful. 

Linux/Unix: How to copy a directory and save the date/time file information alvin April 29, 2019 - 10:57am

If you need to copy a directory on Unix/Linux and want to preserve the date/time information while copying the directory and files, use the -p option to save the date/time information, and the -r option to copy the directory properly. For instance, I just used this cp command to copy a directory named OldDir to a new directory named NewDir, while retaining all of the date/time file information:

Using find and grep to print lines before and after what you’re searching for alvin April 20, 2019 - 10:41am

A cool thing about the Unix/Linux grep command is that you can show lines before and after a pattern match with the -B and -A options. As an example, I just used this combination of find and grep to search for all Scala files under the current directory that contain the string null. This command prints five lines before and after each null line in each file:

$ find . -type f -name "*.scala" -exec grep -B5 -A5 null {} \;

That’s good stuff, but it prints a really long list of lines, and I can’t tell the output of one file from another. To fix this, I put the following code in a file named helper.sh, and made it executable:

Jeyes, a Java version of Xeyes alvin March 10, 2019 - 2:22pm

Jeyes, a Java version of Xeyes

In my spare time back in 2011 I created a Java version of the old Unix/X-Windows “Xeyes” application. If you ever used Xeyes, you know it as a set of eyes that are displayed on-screen, and follow the mouse cursor as you move it around.

Now in 2019 I just brought it back to life, and here’s a 56-second video that shows how it works:

A Scala “Word of the day” shell script

I have a 19" monitor on the counter between my kitchen and living room, and it’s powered by a Raspberry Pi. I use the Linux Phosphor screen saver to show a scrolling “news and stock ticker” on the display, which I’ve programmed to show news from several different sources (Atom and Rss feeds, along with other news and data sources). An old version of the display looks like this:

My Raspberry Pi news ticker display

Today I added a new “Word of the day” feature to the display, and as with all of the other code, I wrote a Scala shell script to generate the output.