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https://github.com/simonbaeumer/shell-tricks

Simple bash tricks which make your life easier.
https://github.com/simonbaeumer/shell-tricks

bash linux posix sh shell tricks

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Simple bash tricks which make your life easier.

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README 

        
# Shell tricks



- [Switch to previous directory](#switch-to-previous-directory)

  * [git](#git)

  * [cd](#cd)

- [Get global ip](#get-global-ip)

- [Simple commands](#simple-commands)

- [Loop](#loop)

- [Loop with specified increment each iteration](#loop-with-specified-increment-each-iteration)

- [Sequences of letters or numbers](#sequences-of-letters-or-numbers)

- [Reuse arguments](#reuse-arguments)

- [Reuse commands](#reuse-commands)

- [Compare output of two commands](#compare-output-of-two-commands)

- [Fix last command](#fix-last-command)

- [Accept interactive commands](#accept-interactive-commands)

- [Last exit code](#last-exit-code)

- [Easy backup](#easy-backup)

- [Print to stderr](#print-to-stderr)

- [Debugging](#debugging)

- [Useful readline tricks](#useful-readline-tricks)

- [Repeat command](#repeat-command)

- [Substrings](#substrings)

- [More resources](#more-resources)

  

## Switch to previous directory



Switch between the current and previous branch / directory. 



### git



```bash

$ git branch

* master

development



$ git checkout development

Switched to branch 'development'

$ git checkout - # Switch to previous

Switched to branch 'master'

$ git checkout -

Switched to branch 'development'

```



### cd



```bash

$ pwd

/

$ cd /tmp

$ cd - # Switch to previous

/

$ cd -

/tmp

```



## Get global ip



```bash

$ curl ifconfig.co # IPv4

50.110.14.21

$ curl -6 ifconfig.co # IPv6

2010:3f3f:113f:0:ea57:4497:7291:e422

```



## Simple commands



Create a script which calls functions by its` first argument. This is very useful to create simple scripts which could be a wrapper for other commands.



```bash

#!/usr/bin/env bash



function do_this () { echo "call do_this function"; }



function do_sth() { echo "call do_sth function" }



case "$1" in

    do_this|do_sth) "$1" ;;

esac

```



Execute it:



```bash

$ ./simple-commands.sh do_this

call do_this function

```



## Loop



Write simple one liner loops if you need to do some batch tasks.



```bash

$ for i in {1..10}; do echo "$i"; done



# List disk usage by directories

$ for file in */ .*/ ; do du -sh $file; done

```



## Loop with specified increment each iteration



```bash

for i in {1..100..2}; do echo $i; done

1

3

5

7

...

```



## Sequences of letters or numbers



Brace expansion is great for lots of things.



``` bash

$ touch file{a..c}

$ ls

$ command ls

filea fileb filec

```



``` bash

$ touch file-{1..15}

$ ls

file-1	file-10	file-11	file-12	file-13	file-14	file-15	file-2	file-3	file-4	file-5	file-6	file-7	file-8	file-9

$ ls file-{9..12}

file-10	file-11	file-12	file-9

```



``` bash

$ printf "%s\n" file-{a..c}{1..3}

file-a1

file-a2

file-a3

file-b1

file-b2

file-b3

file-c1

file-c2

file-c3

```



(If you give `printf` more arguments than it expects, it automatically loops.)



## Reuse arguments



```bash

$ ls /tmp

some_file.txt some_archive.tar.gz

$ cd !$

/tmp

```



## Reuse commands



```bash

$ echo "reuse me"

reuse me

$ !!

echo "reuse me"

reuse me

```



## Compare output of two commands

```bash

diff <(echo "1 2 4") <(echo "1 2 3 4")

1c1

< 1 2 4

---

 > 1 2 3 4

```



## Fix last command



```bash

$ ehco foo bar bar

bash: ehco: command not found

$ ^ehco^echo   

foo bar baz 

```



## Accept interactive commands



```bash

$ yes | ./interactive-command.sh

Are you sure (y/n)

Accepted

yes: standard output: Broken pipe

```



The error message is printed because `yes` gets killed by `SIGPIPE` signal. This happens

if the pipe to `./interactive-command.sh` gets closed but `yes` still wants to write into it.



Ignore error message:



`$ yes 2>/dev/null | ./interactive-command.sh`



## Last exit code



```bash

$ ls /tmp

some_file.txt

$ echo $?

0

```



## Easy backup



```bash

$ cp file.txt{,.bak}

$ ls -1

file.txt

file.txt.bak

```



## Print to stderr



```

$ >&2 echo hello

hello

```



## Debugging



Add `-xv` to your bash scripts, i.e.:



```

/usr/bin/env bash

set -xv

```



or `/bin/bash -xv script.sh`



## Useful `readline` tricks



If you use the standard `bash` `readline` bindings.



- `C-a` (aka `CTRL+A`) move cursor to beginning of line

- `C-e` (aka `CTRL+E`) move cursor to end of line

- `M-.` (aka `ALT+.`)  insert last argument of previous command (like `!$`, but you can edit it)



## Repeat command



Execute a command every two seconds and monitor its` output.

This is especially useful for waiting until a deployment or infrastructure provisioning is completed, i.e. on aws.



`watch -n2 echo hello`

`

## Substrings



```

$ a="apple orange"



$ echo ${a#* }

orange

$ echo ${a#*p}

ple orange

$ echo ${a##*p}

le orange



$ echo ${a% *}

apple

$ echo ${a%p*}

ap

$ echo ${a%%p*}

a

```

The # for finding first occurence from the start and % for the first occurence from the end. * for matching any pattern. For greedy matching ## and %%. 



## More resources



 - [BashFAQ](https://mywiki.wooledge.org/BashFAQ) - A full FAQ of useful stuff