Bash vs Zsh

Zsh is "bash with the rough edges sanded off" — almost script-compatible, much nicer interactively.

Summary

Bash and zsh share ancestry — both descend from the Bourne shell family — so most of what you know about pipes, redirection, conditionals, and command substitution carries over unchanged.

Zsh adds genuinely useful upgrades: smarter tab completion, glob qualifiers (`*(.m-1)` for "modified in the last day"), associative arrays without `declare -A` ceremony, and the plugin ecosystem behind Oh My Zsh / Prezto.

The catch: zsh changes a small set of defaults — word-splitting, array indexing, glob behavior on no-match — that quietly break bash scripts unless you set `emulate sh` or fix the script. Apple shipping zsh as the macOS default since Catalina has not eliminated this footgun.

Syntax & semantic differences

POSIX compatibility
Bash
POSIX-extended. Most POSIX `/bin/sh` scripts run in bash unchanged.
Zsh
Mostly bash-compatible, but with quirks. Use `emulate sh` or `emulate bash` at the top of a script for the closest thing to a clean port.
Word splitting on unquoted variables
Bash
`$var` is split on `$IFS` (default: space/tab/newline) — the source of countless bugs around filenames with spaces.
Zsh
`$var` does **not** split by default. To force bash-style splitting use `${=var}` or `setopt SH_WORD_SPLIT`.
This is the single most common "my script works in bash but breaks in zsh" cause — `for x in $list; do ...` iterates once with the whole string in zsh, not once per word.
Array indexing
Bash
Arrays are 0-indexed. `arr=(a b c); echo ${arr[0]}` prints `a`.
Zsh
Arrays are 1-indexed. `arr=(a b c); echo $arr[1]` prints `a`. `$arr[0]` is empty (or an error under `set -u`).
Off-by-one bugs migrating array code from bash → zsh are common. `${arr[@]}` / `${arr[*]}` still work in both for "all elements".
Glob no-match behavior
Bash
`ls *.nope` → bash echoes the literal pattern `*.nope` (and `ls` then errors). Override with `shopt -s nullglob` / `failglob`.
Zsh
`ls *.nope` → zsh **errors out before running the command** ("no matches found"). Override with `setopt NULL_GLOB` (empty list) or `setopt CSH_NULL_GLOB`.
Glob qualifiers
Bash
No qualifiers — combine `find` + `xargs` or shell loops.
Zsh
Rich qualifiers: `*(.)` (regular files), `*(/)` (directories only), `*(.m-1)` (modified < 1 day), `*(.L+1M)` (larger than 1 MiB), `*(om[1,5])` (5 newest).
Qualifiers are zsh's headline feature. A one-liner like `rm -- *.log(.m+30)` deletes only regular `.log` files older than 30 days — no `find` needed.
Extended globbing
Bash
Enable with `shopt -s extglob`. Patterns: `?(pat)`, `*(pat)`, `+(pat)`, `@(pat)`, `!(pat)`.
Zsh
Enable with `setopt EXTENDED_GLOB`. Different syntax: `(pat|pat)`, `pat~pat` (exclude), `pat#pat` (zero+), `pat##pat` (one+). Not interchangeable.
Associative arrays
Bash
`declare -A map; map[key]=value; echo "${map[key]}"` — requires bash 4+. macOS's default bash is still 3.2 (license reasons).
Zsh
`typeset -A map; map[key]=value; echo $map[key]` — works since zsh 4.x.
Prompt configuration
Bash
`PS1='\u@\h:\w\$ '` with backslash escapes (`\u`, `\h`, `\w`, `\$`, `\[\]` for non-printing).
Zsh
`PROMPT='%n@%m:%~ %# '` with `%`-escapes (`%n`, `%m`, `%~`, `%#`, `%F{red}…%f` for color). Different placeholders entirely.
History file
Bash
`~/.bash_history`. Append on exit. `HISTSIZE` (in memory) + `HISTFILESIZE` (on disk).
Zsh
`~/.zsh_history`. Configurable per-shell append/share with `setopt SHARE_HISTORY` / `INC_APPEND_HISTORY`. `HISTSIZE` + `SAVEHIST`.
Config file
Bash
`~/.bashrc` (interactive non-login) and `~/.bash_profile` / `~/.profile` (login). Sourcing one from the other is a long-standing source of confusion.
Zsh
`~/.zshrc` (interactive), `~/.zprofile` (login), `~/.zshenv` (every shell — even non-interactive scripts). Better separation than bash, but reading `zshenv` for every script can be slow if you stuff it.
Tab completion
Bash
Built-in completion with `bash-completion` package adding most of the polish. `complete -F _func name` registers functions.
Zsh
Completion system (`compinit`) is far richer out of the box — context-aware, with descriptions and menu selection. `autoload -Uz compinit && compinit` in `~/.zshrc`.
Function-local variables
Bash
`local var=value` inside a function. Only visible while the function runs.
Zsh
`local var=value` works the same way. Plus `typeset` and `declare` for explicit type flags.
Substring expansion
Bash
`${var:offset:length}` (0-indexed). `${var:2:3}` of `abcdef` is `cde`.
Zsh
`${var:offset:length}` works, but zsh is 1-indexed by default with `KSH_ARRAYS` unset — `${var[2,4]}` of `abcdef` is `bcd`. Different operator, different indexing.

Side-by-side commands

The 32 most-compared commands in Bash and Zsh. See all Bash commands · See all Zsh commands.

aliasCreate a shortcut name for a longer command line.
Bash
```
alias ll='ls -la'
```
Zsh
```
alias ll='ls -la'
```
awkPattern scanning and processing language for structured text.
Bash
```
awk '{print $1}' file
```
Zsh
```
awk '{print $1}' file
```
catPrint file contents to standard output.
Bash
```
cat file.txt
```
Zsh
```
cat file.txt
```
chmodChange file mode bits (read / write / execute permissions) on Unix files.
Bash
```
chmod 755 file
```
Zsh
```
chmod 755 file
```
cpCopy files and directories.
Bash
```
cp source dest
```
Zsh
```
cp source dest
```
curlTransfer data from or to a server over HTTP, HTTPS, FTP, and many other protocols.
Bash
```
curl https://example.com
```
Zsh
```
curl https://example.com
```
cutExtract sections (fields or characters) from each line.
Bash
```
cut -d',' -f1 file.csv
```
Zsh
```
cut -d',' -f1 file.csv
```
echoPrint arguments to standard output, separated by spaces, followed by a newline.
Bash
```
echo "hello world"
```
Zsh
```
echo "hello world"
```
exportSet an environment variable and mark it for export to child processes.
Bash
```
export NAME=value
```
Zsh
```
export NAME=value
```
findLocate files by name, size, time, or other attributes.
Bash
```
find . -name "*.log"
```
Zsh
```
find . -name "*.log"
```
grepSearch file contents for a pattern.
Bash
```
grep -r "pattern" .
```
Zsh
```
grep -r "pattern" .
```
headOutput the first lines of a file.
Bash
```
head -n 10 file
```
Zsh
```
head -n 10 file
```
historyShow previously run commands from the shell history.
Bash
```
history
```
Zsh
```
history
```
killSend a signal to a process (typically to terminate it).
Bash
```
kill <pid>
```
Zsh
```
kill <pid>
```
lsList directory contents.
Bash
```
ls -la
```
Zsh
```
ls -la
```
mkdirCreate a new directory.
Bash
```
mkdir dir
```
Zsh
```
mkdir dir
```
mvMove or rename files and directories.
Bash
```
mv source dest
```
Zsh
```
mv source dest
```
pingSend ICMP echo requests to test reachability and round-trip latency.
Bash
```
ping example.com
```
Zsh
```
ping example.com
```
psList a snapshot of currently running processes.
Bash
```
ps aux
```
Zsh
```
ps aux
```
rmDelete files and directories.
Bash
```
rm file
```
Zsh
```
rm file
```
sedStream editor for filtering and transforming text.
Bash
```
sed 's/old/new/g' file
```
Zsh
```
sed 's/old/new/g' file
```
sortSort lines of text.
Bash
```
sort file
```
Zsh
```
sort file
```
sshOpen a secure shell on a remote host or run a remote command.
Bash
```
ssh user@host
```
Zsh
```
ssh user@host
```
tailOutput the last lines of a file.
Bash
```
tail -n 10 file
```
Zsh
```
tail -n 10 file
```
tarBundle and unbundle files into a single archive (often combined with gzip / bzip2 / xz).
Bash
```
tar -czf archive.tar.gz dir/
```
Zsh
```
tar -czf archive.tar.gz dir/
```
topInteractive process viewer — show running processes sorted by CPU or memory, refreshed in place.
Bash
```
top
```
Zsh
```
top
```
touchCreate an empty file or update its modification time if it exists.
Bash
```
touch file.txt
```
Zsh
```
touch file.txt
```
wcCount lines, words, or bytes.
Bash
```
wc -l file
```
Zsh
```
wc -l file
```
wgetNon-interactive network downloader for HTTP, HTTPS, and FTP.
Bash
```
wget https://example.com/file.zip
```
Zsh
```
wget https://example.com/file.zip
```
whichLocate an executable in PATH and print its full path.
Bash
```
which python3
```
Zsh
```
which python3
```
xargsBuild and execute command lines from standard input.
Bash
```
find . -name '*.tmp' | xargs rm
```
Zsh
```
find . -name '*.tmp' | xargs rm
```
zipPackage and compress files into a ZIP archive.
Bash
```
zip -r archive.zip dir/
```
Zsh
```
zip -r archive.zip dir/
```

Gotchas when porting between them

Bash scripts that use `read -p` (read with prompt) work in zsh, but `read` without `-p` and a separate `print -n "Prompt: "` is more idiomatic in zsh.
Don't rely on `#!/bin/bash` being bash on Linux but zsh on macOS — `#!/bin/bash` is still `bash` on macOS too (Apple ships an old 3.2 for backwards compatibility). zsh is only the *interactive* default; scripts with `#!/bin/bash` still run under bash.
Zsh's `=` in patterns is the "approximate-match" qualifier under `EXTENDED_GLOB`, not assignment. Pattern `f(=cmd)` matches files named like the result of `which cmd`.
`set -e` works in both, but error propagation through pipelines differs unless you also set `set -o pipefail` (works in both). Without it, only the last command's exit status counts.
Tab-completing a partial path on bash treats `*` as literal; on zsh, `*` may expand and select multiple matches, which can be jarring if you typed it expecting completion.

Bash vs Zsh

Summary

Syntax & semantic differences

POSIX compatibility

Word splitting on unquoted variables

Array indexing

Glob no-match behavior

Glob qualifiers

Extended globbing

Associative arrays

Prompt configuration

History file

Config file

Tab completion

Function-local variables

Substring expansion

Side-by-side commands

Gotchas when porting between them

Full references

Other comparisons