BASH foo ☯

Taking your BASH skills to the next level

A talk by torstein @ escenic

Finding things

Meet your best friend

grep

Meet your 2nd best friend

find

And their cousins

egrep, xargs and |

And their little brothers

wc & cat

With them

You can do incredible things

How many…

Maven modules are there in your project?

$ find -name pom.xml | wc -l

How many…

lines of Java code is there in your project?

$ find -name "*.java" | xargs cat | wc -l

How many…

lines of production Java code? I.e. not tests?

$ find -name "*.java" | grep src/main/java | xargs cat | wc -l

Where is the class used?

$ find -name "*.java" -o -name "*.properties" | \
    grep trunk | \
    grep src/main/java | \
    xargs grep -ni --color IOObjectLoader

Which JAR has my class?

  • Has my class been deployed at all?
  • In which classloader is my class running?
  • Are there multiple versions of my class deployed?

Which JAR has my class?

Don’t look at your IDEA project structure and guess.

Which JAR has my class?

$ grep -r com.example.app.MyClass /opt/tomcat*

Which JAR has my class?

What’s the problem with grep here?

Can we do better?

Which JAR has my class?

$ find -L /opt/tomcat -name "*.jar" | \
  xargs grep com.example.app.MyClass

Which JAR has my class?

What’s the problem with find and grep here?

Can we do better?

Which JAR has my class?

$ find -L /opt/tomcat -name "*.jar" | \
  while read f; do \
    echo $f;
    unzip -t $f | grep com.example.app.MyClass; \
  done

Can we do better?

Which JAR has my class?

$ /opt/escenic/engine/bin/find-jar \
  /opt/tomcat \
  com.example.app.MyClass

It remembers 🐘

How was that ssh command again?

It remembers 🐘

↑ ↑ ↑

It remembers 🐘

$ history

It remembers 🐘

$ grep ssh ~/.bash_history

It remembers 🐘

Ctrl + r

(reverse-i-search)`ssh': ssh -L 99:localhost:80 foo@login.example.com

Yes, you can ✈

Yes, you can ✈

At the start Ctrl + a

‐

End of line.: Ctrl + e

‐

Delete letter: Ctrl + d

‐

Kill the rest: Ctrl + k

Yes, you can ✈ II

Delete word Alt + d

‐

Delete pevious word: Alt + ←

‐

Uppercase word: Alt + u

‐

Lowercase word: Alt + l

SSH

Passwordless logins

$ ssh-keygen -t rsa
$ ssh-copy-id user@host
$ ssh user@host

Different usernames

Different usernames on different servers

Host *.dev.example.com
     User frodo

TAB completion

Install & enable BASH completion:

# apt-get install bash-completion
$ echo "source /usr/share/bash-completion/bash_completion" \
  >> ~/.bashrc
$ source ~/.bashrc

TAB completion - II

Be sure that your system doesn’t hash the host names in ~/.ssh/known_hosts:

$ echo "HashKnownHosts no" >> ~/.ssh/config

TAB completion - III

$ ssh p[TAB][TAB]
p4.dev.example.com
projects.example.com

Reverse tunnels

Super useful. Makes life bearable in a world of stubborn sys admins.

Reverse tunnels

$ ssh -L 9980:localhost:80 closy

Now, browse http://localhost:9980 and you’ll be in fact accessing http://closy:80

Reverse tunnels

You may want to set the Host header right

# echo 127.0.0.1 closy >> /etc/hosts

Now, you can use http://closy:9980 passing the correct Host header through the tunnel to your target system.

Reverse tunnels

If the CLI is enough:

$ curl -H "Host: closy" http://localhost:9980

Loops

What did I do last week?

$ p4 changes | grep 2015/08/03

Can we do better?

What did I do last week?

$ for el in 3 4 5 6 7 ; do p4 changes | grep 2015/08/0${el}; done

Can we do better?

What did I do last week?

$ for el in {3..7} ; do p4 changes | grep 2015/08/0${el}; done

Can we do better?

What did I do last week?

$ for el in {03..7} ; do p4 changes | grep 2015/08/${el}; done

Don’t be good, be great

Don’t be good, be great

How to use ssh? Read the man pages!

$ man ssh

Don’t be good, be great

Searching man will open your eyes:

$ man -k ssh

Fine

✏ torstein @ escenic dot com

@torsteinkrause