Why?

The terminal of UNIX based operating systems is insanely powerful, hence owning this power takes a lifetime. While learning it there are few tips and tricks that you can keep handy which will make you super productive. This document would be forever in Work in Progress mode and as I keep coming across any tips, I’ll be documenting them here.

tips

• Sometimes we need super-user (sudo) privilege to run a command, but we realize it only after executing it. Hence when we try to run the command again we either rewrite the entire command or use the up arrow key to get it again then edit it. But there is a simple way to do it. Use sudo !! to run the previously executed command with sudo privilege.

• How to list the last three newly created files in a directory?
  ls -ltr | tail -3

• How to send last three newly created files in a directory to a server?
  scp `ls -ltr | tail -3` username@<ip>:<location>

• ? variable stores the exit status code of last executed unix or linux shell command. If the value of ? is 0 then it means that the last command executed successfully, but it it’s non-zero, that means there was some error.
  Eg.
  

• Compress a directory:

  • fast- tar -cv /path/to/dir | gzip --fast newFileName.tar.gz (fast compression)
  • best- tar -cv /path/to/dir | gzip --best newFileName.tar.gz (best compression)

• pigz is a parallel implementation of gzip is much faster when compressing multiple number of files:
  tar -cv source-dir/ | pigz --best > target-file-name.tar.gz

• You can use find and sed to replace a particular string with another string, accross all the files in a directory using the following command: for i in $(find pkg -type f -name "*_test.go"); do echo "Checking file $i:"; sed -i -e 's/common\//github.com\/ArecaBay\/service\/pkg\//g' $i ; echo ""; done Here, I’m substituting all the occurances of the pattern “common/” with “github.com/ArecaBay/service/pkg/” in all files with suffix “_test.go” in the directory “pkg”.

  NOTE: When you run sed, it creates backup files with the suffix “-e”, hence if you want to clean all those backup files you can run find . -name "*-e*" -type f -delete

• It is useful to run some commands automatically when certain files change, like, I want to run go install in my working directory every time I edit any go file. You can do it using this tool https://github.com/cespare/reflex using the following command:

  reflex -r '\.go' go install

  Bonus tip: nohup it using the following command to run in the background and ignore the input and append output to .out file to avoid activity on screen.:

  nohup reflex -r '\.go' go install &

  You can of course control the background processes using jobs command afterwards.

  If you’re using vim you can run it async using AsyncRun plugin using:

  AsyncRun reflex -r .go go install

  This will enable use you to look out for compilation errors in the quickfix window easily. (’:copento open and:cclose` to close)