/bash-by-example

Primary LanguageShell

bash-by-example

Introduction

Some notes and examples of bash commands and common command line utilities I frequently use from bash.

A lot of the examples here are similar to stackoverflow threads, but here I get to record my favorite solutions and demo why I like them and give some extra context?

example 18 - setting terminal on new macbook

Add iterm2 via brew:

brew install --cask iterm2

Add the following shortcuts

alias h='history'
alias h40='history|tail -40'
alias hl='history|less'
alias l40='ls -ltr|tail -40'
alias lt='ls -ltr|tail -10'
alias ht='history|tail -10'

Set bash to the default shell

# https://superuser.com/questions/48226/how-do-i-set-my-shell-in-mac-os-x
chsh -s /bin/bash

example 17 - getting started with conda and jupyter notebook

  • Download anacondo

https://www.anaconda.com/products/distribution

  • Setup pandas_playground
conda info --envs
conda activate pandas_playground
conda install pandas jupyter bottleneck numexpr matplotlib
conda update --all
  • Final from terminal
jupyter notebook

example 16 - psql - probably the best command line db editor

  • psql -E or set ECHO_HIDDEN to pg_catalog metadata - VERY USEFUL - details here

example 15 - bash loop with limit $1

I've been struggling with running bash loops with input parameters of the format {1..$1} ... this never quite works for me (I've tried a few iterations).

The solution appears to be to use a while loop

[root@c7-master vagrant]# cat loop.sh 
#echo $1
i=1
while [ "$i" -le "$1" ]; do
   uptime
   sleep 2
   i=$((i+1))
   #echo $i
done

e.g.

[root@c7-master vagrant]# bash loop.sh 3
 21:26:02 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
 21:26:04 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
 21:26:06 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
[root@c7-master vagrant]# bash loop.sh 4
 21:26:10 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
 21:26:12 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
 21:26:14 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
 21:26:16 up 19 days, 50 min,  2 users,  load average: 0.00, 0.01, 0.05
[root@c7-master vagrant]#

example 014 - which: command not found

I thought which was part of the standard bash shell, apparently not

-bash-4.2$ which psql
-bash: which: command not found
-bash-4.2$ exit                     
logout
-bash-4.2# yum install -y which
Loaded plugins: ovl
Resolving Dependencies
--> Running transaction check
---> Package which.x86_64 0:2.20-7.el7 will be installed
--> Finished Dependency Resolution

I suspect which is standard for rhel and ubuntu, but maybe not in more minimal docker linux images?

example 013 - adding an alias

Starting with projects directory

[~] # ls -l | grep proj
drwxrwxr-x 26 dpitts     4096 feb 13 23:26 projects/

create an alias scripts

[~] # ln -s projects scripts
[~] # ls -l | grep proj
drwxrwxr-x 26 dpitts     4096 feb 13 23:26 projects/
lrwxrwxrwx  1 dpitts        8 feb 18 23:01 scripts -> projects/

example 012 - simple load testing via pgbench

example_011 atop - yum install and config

example_010 extra_alias_start_stop_postgres

Some custom extra alias

example_009 chmod_read_write_exec

While git does not support write-only access this is common elsewhere

example_008 bash_awk_sum_stddev

Using awk to calculate sum and stddev

example_007 find_xargs_grepH

find with xargs and grep -H for deep search

example_006 introducing_ShellCheck (to be completed)

RHEL setup shellcheck

example_005 awk_special_characters

awk escape characters, single quote and new_lines

example_004 getting_started_with_git

intro to git cli

example_003 vscode-bash-debug_setup_and_brew

  • While I've routinely worked with bash directly on the command-line (on a daily basis) for almost the last two decades (in the early days I was using ksh and csh), more recently I've started using Visual Studio Code and a debugger extension
  • https://github.com/rogalmic/vscode-bash-debug
  • https://code.visualstudio.com/docs/editor/debugging
  • There are no new scripts here, but some code samples and I do cover different bash versions, in the context of macosx and using brew (the package manager for macosx) to install a second and newer version of bash

example_002 bash_random_and_awk_95th_percentile

  • generate 30000 random numbers before 0 and 9999
  • use awk to sort list and extract the 95th percentile, which should be 'around 9500' +/-100 (i.e. between 9400 and 9600))

example_001 input_flags to scripts and if then elif fi blocks

Appendix - background references