Differences between zsh and bash

Published on: 2022-04-11

Introduction

This article aims only to differences between zsh and bash. Author has no experiences with others. Both of them are categorized as unix shells.

## Sh (Bourne Shell) This unix shell is not a subject of this article, but I’d like to mention it because its name Bourne shell could be confused as bash by beginners. This shell was created in 1977 by Stephen R. Bourne, who worked in AT&T Bell Laboratories. This shell can be found in most of today’s unix computers under the path /bin/sh. Bourne shell was a replacement for the Thompson shell, whose executable file had the same path /bin/sh.

Bash (Bourne again shell)

Bash is unix POSIX shell which was created by Free Software Foundation (FSF). Development started in 1988 by Brian Fox as replacement for sh. Syntax of bash is a superset of the Bourne shell. It can call it as extension of the bourne shell or advanced bourne shell, because bash has a lot extra features against to bourne shell, but syntax is preserved as the bourne shell. Bash is used in most of nowadays linux distributions as default shell under the path /bin/bash. MacOS used bash as default shell until 2019, when they’ve switched to zsh. One of reason why Apple chnaged was a new license GPL-3.0 for bash 4.0.

## Zsh (Z shell) Zsh is also unix shell under license MIT. Zsh is extended bourne shell with much improvements. Zsh also added some really favorite functions from ksh, bash and tcsh. Original author of zsh was Paul Falstad who created the zsh during his study on Princeton University and the name of zsh was created by his professor Zhong Shao. Zsh can be call as command and programming language. zsh is used in MacOS or Kali Linux nowadays. Path to execute this shell is /bin/zsh.

Differences between ZSH and BASH

## Word splitting upon parameter expansion

Word Splitting Space is taken as special char which separate each arguments and commands. So if we save some text with spaces to shell variable, we have to remember, when we’d like to expansion this variable.

Parameter Expansion (Substitution) If we want to use expansion we have to use dollar-sign as syntax. When we use dollar-sign before to var name, content of variable will expand to command line and we can use the content with some command.

bash

$ /bin/bash
$ a="a b c d"
$ printf '<%s>\n' $a
<a>
<b>
<c>
<d>

As you can see in example above, parameter expansion evaluate each word separate by space as one argument for command printf. If we dont want to allow word splitting after parameter expansion we have to put the expansion to double-quotes “ in bash.

$ /bin/bash
$ a="a b c d"
$ printf '<%s>\n' "$a"
<a b c d>

But this approach will not work in zsh, because word splitting is disable by default. So there is opposite situation how enable word splitting upon parameter expansion?

zsh

Word splitting is disable by default

$ /bin/zsh
$ a="a b c d"
$ printf '<%s>\n' $a
<a b c d>

It does not matter in zsh if we used double-quotes to disable word splitting upon parameter expansion (or substition) because of default disabled value.

$ /bin/zsh
$ a="a b c d"
$ printf '<%s>\n' "$a"
<a b c d>

So if we want to use word splitting we have to use special syntax = for perform word splitting.

$ /bin/zsh
$ a="a b c d"
$ printf '<%s>\n' $=a
<a>
<b>
<c>
<d>

Word splitting upon parametr expansion could be set globally with option shwordsplit.

Globbing pattern upon parameter expansion

Glob is command which is able to match filenames by pattern which we created. Paterrns consists of basic wildcards as:

, where each wildcard has own special meaning. Dont confuse globbing with regex. Although it is similar concept, there is absolutely different usage. By default glob does not match hidden files start with dot ..

Glob pattern can be saved in shell variable. There occurs problem with parameter (variable) expansion again.

bash

$ /bin/bash
$ a=*
$ ls $a
a.txt   b.txt   c.txt   d.txt

As you can see in example above, expansion is proceeded that asterisk is taken as glob wildcard.

$ /bin/bash
$ a=*
$ ls "$a"
ls: *: No such file or directory

When we used double-quoutes, asterisk is used as text (string) after expansion and command takes asterisk as filename not as wildcard. If we’ve really created file with name * then ls will not invoke exception.

zsh

Globbing upon parameter expansion is disabled by default, so asterisk is not used as pattern for globbing but like filename.

$ /bin/zsh
$ a=*
$ ls $a
ls: *: No such file or directory

If we want to enable pattern globbing after expansion we have to use special syntax ~.

$ /bin/zsh
$ a=*
$ ls $~a
a.txt b.txt c.txt d.txt

We can use different approach and save to parameter at the beginning by running glob pattern in subshell. Subshell start by run the command in simple parentheses. So during expansion there will not be the asterisk char but filenames matched by glob in subshell.

$ /bin/zsh
$ a=( * )
$ ls $a
a.txt b.txt c.txt d.txt

Globbing upon parametr expansion could be set in zsh globally with option globsubst.

## ZSH word split and glob expansion together There is also option to combine special syntax for * word splitting upon expansion = * and globbing upon expansion ~.

$ /bin/zsh
$ $=~a

Useful links