A visual reference · Bash

Bash,
one change at a time

From a first command to small, reliable shell programs. Complete source. A small change. Its actual result.

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Last changes: 2026-10-19. Added a searchable HTML gallery with code-and-output previews, labelled Zsh comparisons and links to complete examples and back. Every tour now links to tours.emaix.org. Unified tour–chapter–example IDs, numbered chapter anchors and updated direct links, downloads and comparisons. Added nine worked examples for here-strings, variable-name expansion and ERR traps, with an expanded quick reference and a Devhints cheatsheet link. Reader pages now omit publishing instructions and highlight PDF downloads.

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152worked examples

21topic families

1canonical Org source

Browse by code and result

All shell examples at a glance

152 examples · 21 topics

Choose a preview to open the complete program and captured result. Search examples or select a topic to narrow the gallery. An ellipsis marks shortened code or output.

First commands and formatted output

6 examples

BSH-01-001

Print a line

Code preview

printf '%s\n' 'Hello, shell!'

Bash · exit 0

Hello, shell!

View complete example

BSH-01-002

One argument, one line

Code preview

printf '%s\n' 'alpha' 'beta'

Bash · exit 0

alpha
beta

View complete example

BSH-01-003

Keep words together

Code preview

printf '<%s>\n' 'alpha beta' gamma

Bash · exit 0

<alpha beta>
<gamma>

View complete example

BSH-01-004

Align columns

Code preview

printf '%-8s %04d\n' apples 7 pears 12

Bash · exit 0

apples   0007
pears    0012

View complete example

BSH-01-005

Choose decimal precision

Code preview

printf 'mean = %.2f\n' 3.14159

Bash · exit 0

mean = 3.14

View complete example

BSH-01-006

Comments and continuation

Code preview

# Two physical lines, one command
printf '%s\n' \
  'continued command'

Bash · exit 0

continued command

View complete example

Variables and quoting

6 examples

BSH-02-001

Assign and expand

Code preview

label='sample A'
printf '<%s>\n' "$label"

Bash · exit 0

<sample A>

View complete example

BSH-02-002

Single versus double quotes

Code preview

label='sample A'
printf '%s\n' '$label' "$label"

Bash · exit 0

$label
sample A

View complete example

BSH-02-003

Bash splits an unquoted scalar

Code preview

label='sample A'
printf '<%s>\n' $label

Bash · exit 0

<sample>
<A>

View complete example

BSH-02-004Zsh comparison

Zsh difference: keeps an unquoted scalar

Code preview

label='sample A'
printf '<%s>\n' $label

Zsh · exit 0

<sample A>

View complete example

BSH-02-005Zsh comparison

Zsh difference: Explicit Zsh splitting

Code preview

label='sample A'
printf '<%s>\n' ${=label}

Zsh · exit 0

<sample>
<A>

View complete example

BSH-02-006

Protect a variable boundary

Code preview

label=sample
printf '%s\n' "${label}_final"

Bash · exit 0

sample_final

View complete example

Parameter expansion and arithmetic

8 examples

BSH-03-001

A fallback value

Code preview

unset label
printf '%s\n' "${label:-untitled}"

Bash · exit 0

untitled

View complete example

BSH-03-002

Unset versus empty

Code preview

label=''
printf 'colon=<%s> plain=<%s>\n' "${label:-fallback}" "${label-fallback}"

Bash · exit 0

colon=<fallback> plain=<>

View complete example

BSH-03-003

Assign the fallback

Code preview

unset label
printf '%s\n' "${label:=untitled}" "$label"

Bash · exit 0

untitled
untitled

View complete example

BSH-03-004

Remove a suffix

Code preview

file='sample.raw.csv'
printf '%s\n' "${file%.csv}"

Bash · exit 0

sample.raw

View complete example

BSH-03-005

Shortest versus longest match

Code preview

file='sample.raw.csv'
printf '%s\n' "${file%.*}" "${file%%.*}"

Bash · exit 0

sample.raw
sample

View complete example

BSH-03-006

Remove a path prefix

Code preview

file='data/raw/sample.csv'
printf '%s\n' "${file##*/}"

Bash · exit 0

sample.csv

View complete example

BSH-03-007

Replace matching text

Code preview

label='a-b-c'
printf '%s\n' "${label/-/_}" "${label//-/_}"

Bash · exit 0

a_b-c
a_b_c

View complete example

BSH-03-008

Integer arithmetic

Code preview

n=7
printf '%s\n' "$((n + 2))" "$((n / 2))" "$((n % 2))"

Bash · exit 0

9
3
1

View complete example

Files and filename patterns

9 examples

BSH-04-001

Create, copy and read

Code preview

mkdir data
printf '%s\n' alpha > data/input.txt
cp data/input.txt data/copy.txt
cat data/copy.txt

Bash · exit 0

alpha

View complete example

BSH-04-002

Select a filename suffix

Code preview

touch a.txt b.txt c.csv
printf '%s\n' *.txt

Bash · exit 0

a.txt
b.txt

View complete example

BSH-04-003

A quoted pattern stays literal

Code preview

touch a.txt b.txt c.csv
printf '%s\n' '*.txt'

Bash · exit 0

*.txt

View complete example

BSH-04-004

Exactly one character

Code preview

touch a1.txt a2.txt b1.txt aa1.txt
printf '%s\n' [ab]?.txt

Bash · exit 0

a1.txt
a2.txt
b1.txt

View complete example

BSH-04-005

Brace expansion does not find files

Code preview

printf '%s\n' sample_{A,B}.csv

Bash · exit 0

sample_A.csv
sample_B.csv

View complete example

BSH-04-006

Bash unmatched glob

Code preview

printf '<%s>\n' missing*.csv

Bash · exit 0

<missing*.csv>

View complete example

BSH-04-007Zsh comparison

Zsh difference: unmatched glob

Code preview

printf '<%s>\n' missing*.csv

Zsh · exit 1

(no stdout)

Standard error

zsh:1: no matches found: missing*.csv

View complete example

BSH-04-008

Bash: collect zero matches

Code preview

shopt -s nullglob
files=(missing*.csv)
printf 'files=%s\n' "${#files[@]}"

Bash · exit 0

files=0

View complete example

BSH-04-009Zsh comparison

Zsh difference: collect zero matches

Code preview

files=(missing*.csv(N))
printf 'files=%s\n' "${#files[@]}"

Zsh · exit 0

files=0

View complete example

Streams, redirection and pipes

13 examples

BSH-05-001

Write a file

Code preview

printf '%s\n' alpha > notes.txt
cat notes.txt

Bash · exit 0

alpha

View complete example

BSH-05-002

Append instead

Code preview

printf '%s\n' alpha > notes.txt
printf '%s\n' beta >> notes.txt
cat notes.txt

Bash · exit 0

alpha
beta

View complete example

BSH-05-003

Read standard input

Code preview

printf '%s\n' alpha > notes.txt
tr 'a-z' 'A-Z' < notes.txt

Bash · exit 0

ALPHA

View complete example

BSH-05-004

Connect two commands

Code preview

printf '%s\n' alpha beta | tr 'a-z' 'A-Z'

Bash · exit 0

ALPHA
BETA

View complete example

BSH-05-005

Sort and count repeats

Code preview

printf '%s\n' pear apple pear | sort | uniq -c

Bash · exit 0

   1 apple
   2 pear

View complete example

BSH-05-006

Separate stdout and stderr

Code preview

printf '%s\n' result
printf '%s\n' diagnostic >&2

Bash · exit 0

result

Standard error

diagnostic

View complete example

BSH-05-007

Capture both streams

Code preview

{ printf 'result\n'; printf 'diagnostic\n' >&2; } > log.txt 2>&1
cat log.txt

Bash · exit 0

result
diagnostic

View complete example

BSH-05-008

Redirection order matters

Code preview

{ printf 'result\n'; printf 'diagnostic\n' >&2; } 2>&1 > log.txt
printf 'FILE:\n'
cat log.txt

Bash · exit 0

diagnostic
FILE:
result

View complete example

BSH-05-009

A literal here-document

Code preview

label=sample
cat <<'TEXT'
$label is literal here.
TEXT

Bash · exit 0

$label is literal here.

View complete example

BSH-05-010

An expanding here-document

Code preview

label=sample
cat <<TEXT
$label is expanded here.
TEXT

Bash · exit 0

sample is expanded here.

View complete example

BSH-05-011

Save and continue a stream

Code preview

printf 'alpha\n' | tee copy.txt | tr 'a-z' 'A-Z'
cat copy.txt

Bash · exit 0

ALPHA
alpha

View complete example

BSH-05-012

Feed a variable through a here-string

Code preview

text='alpha beta'
tr '[:lower:]' '[:upper:]' <<< "$text"

Bash · exit 0

ALPHA BETA

View complete example

BSH-05-013

An empty here-string still supplies a line

Code preview

text=''
IFS= read -r line <<< "$text"
printf 'here-string: status=%s length=%s\n' "$?" "${#line}"
printf '%s' "$text" | {
…

Bash · exit 0

here-string: status=0 length=0
printf: status=1 length=0

View complete example

Exit status and decisions

8 examples

BSH-06-001

Read the exit status

Code preview

false
printf 'status=%s\n' "$?"

Bash · exit 0

status=1

View complete example

BSH-06-002

Run only after success

Code preview

true && printf 'runs\n'
false && printf 'skipped\n'
printf 'done\n'

Bash · exit 0

runs
done

View complete example

BSH-06-003

Recover after failure

Code preview

false || printf 'fallback\n'

Bash · exit 0

fallback

View complete example

BSH-06-004

Branch on a number

Code preview

n=7
if [[ "$n" -gt 5 ]]; then
  printf 'large\n'
else
…

Bash · exit 0

large

View complete example

BSH-06-005

Match a string pattern

Code preview

file='sample.csv'
if [[ "$file" == *.csv ]]; then
  printf 'CSV input\n'
fi

Bash · exit 0

CSV input

View complete example

BSH-06-006

Several alternatives with case

Code preview

file='sample.tsv'
case "$file" in
  *.csv) printf 'comma\n' ;;
  *.tsv) printf 'tab\n' ;;
…

Bash · exit 0

tab

View complete example

BSH-06-007

Default pipeline status

Code preview

false | cat
printf 'pipeline=%s\n' "$?"

Bash · exit 0

pipeline=0

View complete example

BSH-06-008

Enable pipefail

Code preview

set -o pipefail
false | cat
printf 'pipeline=%s\n' "$?"

Bash · exit 0

pipeline=1

View complete example

Loops, arguments and functions

8 examples

BSH-07-001

Loop over explicit arguments

Code preview

for item in alpha 'beta gamma'; do
  printf '<%s>\n' "$item"
done

Bash · exit 0

<alpha>
<beta gamma>

View complete example

BSH-07-002

Read complete lines

Code preview

printf '%s\n' '  alpha' 'a\b' > lines.txt
while IFS= read -r line; do
  printf '<%s>\n' "$line"
done < lines.txt

Bash · exit 0

<  alpha>
<a\b>

View complete example

BSH-07-003

Repeat while a condition holds

Code preview

n=0
while [[ "$n" -lt 3 ]]; do
  printf '%s\n' "$n"
  n=$((n + 1))
…

Bash · exit 0

0
1
2

View complete example

BSH-07-004

Preserve positional arguments

Code preview

set -- alpha 'beta gamma'
printf 'count=%s\n' "$#"
printf '<%s>\n' "$@"

Bash · exit 0

count=2
<alpha>
<beta gamma>

View complete example

BSH-07-005

Join positional arguments

Code preview

set -- alpha 'beta gamma'
printf '<%s>\n' "$*"

Bash · exit 0

<alpha beta gamma>

View complete example

BSH-07-006

A function with an argument

Code preview

greet() {
  local person="$1"
  printf 'Hello, %s!\n' "$person"
}
…

Bash · exit 0

Hello, Ada Lovelace!

View complete example

BSH-07-007

Capture a command result

Code preview

greet() { printf 'Hello, %s!\n' "$1"; }
message=$(greet Ada)
printf '<%s>\n' "$message"

Bash · exit 0

<Hello, Ada!>

View complete example

BSH-07-008

Return a status from a function

Code preview

is_csv() { [[ "$1" == *.csv ]]; }
if is_csv sample.csv; then printf 'accepted\n'; fi

Bash · exit 0

accepted

View complete example

Arrays and mappings

8 examples

BSH-08-001

Bash starts at index zero

Code preview

items=(alpha 'beta gamma')
printf '%s\n' "${items[0]}" "${items[1]}"

Bash · exit 0

alpha
beta gamma

View complete example

BSH-08-002Zsh comparison

Zsh difference: starts at index one

Code preview

items=(alpha 'beta gamma')
printf '%s\n' "${items[1]}" "${items[2]}"

Zsh · exit 0

alpha
beta gamma

View complete example

BSH-08-003

Preserve array elements

Code preview

items=(alpha 'beta gamma')
printf 'count=%s\n' "${#items[@]}"
printf '<%s>\n' "${items[@]}"

Bash · exit 0

count=2
<alpha>
<beta gamma>

View complete example

BSH-08-004

Append an array element

Code preview

items=(alpha)
items+=('beta gamma')
printf '<%s>\n' "${items[@]}"

Bash · exit 0

<alpha>
<beta gamma>

View complete example

BSH-08-005

Bash associative array

Code preview

declare -A units
units[mass]=kg
units[time]=s
printf '%s\n' "${units[mass]}"

Bash · exit 0

kg

View complete example

BSH-08-006Zsh comparison

Zsh difference: associative array

Code preview

typeset -A units
units[mass]=kg
units[time]=s
printf '%s\n' "${units[mass]}"

Zsh · exit 0

kg

View complete example

BSH-08-007Zsh comparison

Zsh difference: split and join flags

Code preview

text='alpha,beta,gamma'
items=("${(@s:,:)text}")
printf '%s\n' "${(j: / :)items}"

Zsh · exit 0

alpha / beta / gamma

View complete example

BSH-08-008Zsh comparison

Zsh difference: path modifiers

Code preview

file='data/sample.csv'
printf '%s\n' "${file:t}" "${file:h}" "${file:r}"

Zsh · exit 0

sample.csv
data
data/sample

View complete example

Processes, isolation and robust scripts

8 examples

BSH-09-001

A subshell isolates assignments

Code preview

n=1
(n=2; printf 'inside=%s\n' "$n")
printf 'outside=%s\n' "$n"

Bash · exit 0

inside=2
outside=1

View complete example

BSH-09-002

A group shares assignments

Code preview

n=1
{ n=2; printf 'inside=%s\n' "$n"; }
printf 'outside=%s\n' "$n"

Bash · exit 0

inside=2
outside=2

View complete example

BSH-09-003

Export to a child process

Code preview

export TOUR_LABEL=sample
bash --noprofile --norc -c 'printf "%s\n" "$TOUR_LABEL"'

Bash · exit 0

sample

View complete example

BSH-09-004

Wait for a background job

Code preview

(exit 7) &
job_pid=$!
wait "$job_pid"
printf 'job status=%s\n' "$?"

Bash · exit 0

job status=7

View complete example

BSH-09-005

Process substitution

Code preview

diff <(printf 'b\na\n' | sort) <(printf 'a\nb\n')
printf 'diff status=%s\n' "$?"

Bash · exit 0

diff status=0

View complete example

BSH-09-006

Unset variables become errors

Code preview

set -u
unset missing
printf '%s\n' "$missing"

Bash · exit 127

(no stdout)

Standard error

bash: line 3: missing: unbound variable

View complete example

BSH-09-007

A fallback works with nounset

Code preview

set -u
unset missing
printf '%s\n' "${missing:-fallback}"

Bash · exit 0

fallback

View complete example

BSH-09-008

Cleanup on shell exit

Code preview

printf 'temporary\n' > scratch.txt
trap 'rm -f scratch.txt; printf "cleaned up\n"' EXIT
cat scratch.txt

Bash · exit 0

temporary
cleaned up

View complete example

A small reproducible report

3 examples

BSH-10-001

Stage a tiny dataset

Code preview

cat > measurements.tsv <<'DATA'
sample	value
A	3
B	7
…

Bash · exit 0

sample	value
A	3
B	7
C	5

View complete example

BSH-10-002

Validate before processing

Code preview

printf 'sample\tvalue\nA\t3\n' > measurements.tsv
if [[ ! -r measurements.tsv || ! -s measurements.tsv ]]; then
  printf 'missing input\n' >&2
  exit 1
…

Bash · exit 0

input accepted

View complete example

BSH-10-003

Compute and write a report

Code preview

printf 'sample\tvalue\nA\t3\nB\t7\nC\t5\n' > measurements.tsv
awk 'NR>1 {sum+=$2; n++}
     END {printf "samples=%d\nmean=%.2f\n", n, sum/n}' \
  measurements.tsv > report.txt
…

Bash · exit 0

samples=3
mean=5.00

View complete example

Filename-safe processing

6 examples

BSH-11-001

Keep a space inside a filename

Code preview

touch 'sample A.txt' 'sample B.txt'
files=(*.txt)
for file in "${files[@]}"; do
  printf '<%s>\n' "$file"
…

Bash · exit 0

<sample A.txt>
<sample B.txt>

View complete example

BSH-11-002

A leading dash is still a filename

Code preview

printf 'contents\n' > ./-n
cat ./-n

Bash · exit 0

contents

View complete example

BSH-11-003

Read NUL-separated records

Code preview

printf '%s\0' 'sample A.txt' 'sample B.txt' > names.bin
while IFS= read -r -d '' file; do
  printf '<%s>\n' "$file"
done < names.bin

Bash · exit 0

<sample A.txt>
<sample B.txt>

View complete example

BSH-11-004

Process the last unterminated line

Code preview

printf 'alpha\nbeta' > lines.txt
while IFS= read -r line || [[ -n "$line" ]]; do
  printf '<%s>\n' "$line"
done < lines.txt

Bash · exit 0

<alpha>
<beta>

View complete example

BSH-11-005

Read two fields

Code preview

printf 'sample:7:kg\n' > data.txt
while IFS=: read -r name rest; do
  printf 'name=%s rest=%s\n' "$name" "$rest"
done < data.txt

Bash · exit 0

name=sample rest=7:kg

View complete example

BSH-11-006

Skip a file deliberately

Code preview

for file in a.csv notes.txt b.csv; do
  [[ "$file" == *.csv ]] || continue
  printf 'process %s\n' "$file"
done

Bash · exit 0

process a.csv
process b.csv

View complete example

Script options one step at a time

6 examples

BSH-12-001

Consume one argument

Code preview

set -- alpha beta gamma
printf 'before=%s\n' "$1"
shift
printf 'after=%s count=%s\n' "$1" "$#"

Bash · exit 0

before=alpha
after=beta count=2

View complete example

BSH-12-002

Parse a short flag

Code preview

set -- -v
OPTIND=1
verbose=no
while getopts ':v' opt; do
…

Bash · exit 0

verbose=yes

View complete example

BSH-12-003

An option with a value

Code preview

set -- -n 'sample A'
OPTIND=1
while getopts ':n:' opt; do
  case "$opt" in n) printf 'name=%s\n' "$OPTARG" ;; esac
…

Bash · exit 0

name=sample A

View complete example

BSH-12-004

Keep the remaining filenames

Code preview

set -- -n demo -- 'sample A.csv' b.csv
OPTIND=1
while getopts ':n:' opt; do
  case "$opt" in n) printf 'name=%s\n' "$OPTARG" ;; esac
…

Bash · exit 0

name=demo
file=<sample A.csv>
file=<b.csv>

View complete example

BSH-12-005

Report a missing option value

Code preview

set -- -n
OPTIND=1
while getopts ':n:' opt; do
  case "$opt" in
…

Bash · exit 2

(no stdout)

Standard error

missing value: -n

View complete example

BSH-12-006

Report an unknown option

Code preview

set -- -x
OPTIND=1
while getopts ':n:' opt; do
  case "$opt" in
…

Bash · exit 2

(no stdout)

Standard error

unknown option: -x

View complete example

Pipeline scope and status details

6 examples

BSH-13-001

Bash: pipeline assignment disappears

Code preview

value=before
printf 'after\n' | read -r value
printf '%s\n' "$value"

Bash · exit 0

before

View complete example

BSH-13-002Zsh comparison

Zsh difference: final pipeline assignment persists

Code preview

value=before
printf 'after\n' | read -r value
printf '%s\n' "$value"

Zsh · exit 0

after

View complete example

BSH-13-003

Use redirection to preserve state

Code preview

value=before
read -r value < <(printf 'after\n')
printf '%s\n' "$value"

Bash · exit 0

after

View complete example

BSH-13-004

Bash: inspect every pipeline status

Code preview

false | true | false
codes=("${PIPESTATUS[@]}")
printf '%s\n' "${codes[@]}"

Bash · exit 0

1
0
1

View complete example

BSH-13-005Zsh comparison

Zsh difference: inspect every pipeline status

Code preview

false | true | false
codes=("${pipestatus[@]}")
printf '%s\n' "${codes[@]}"

Zsh · exit 0

1
0
1

View complete example

BSH-13-006

A command substitution trims newlines

Code preview

value=$(printf 'alpha\n\n')
printf '<%s> length=%s\n' "$value" "${#value}"

Bash · exit 0

<alpha> length=5

View complete example

More patterns and array operations

8 examples

BSH-14-001

Include hidden files in Bash

Code preview

touch visible.txt .hidden.txt
shopt -s dotglob nullglob
files=(*.txt)
printf '%s\n' "${files[@]}"

Bash · exit 0

.hidden.txt
visible.txt

View complete example

BSH-14-002Zsh comparison

Zsh difference: Include hidden files in Zsh

Code preview

touch visible.txt .hidden.txt
files=(*.txt(DN))
printf '%s\n' "${files[@]}"

Zsh · exit 0

.hidden.txt
visible.txt

View complete example

BSH-14-003Zsh comparison

Zsh difference: regular files only

Code preview

mkdir data
 touch a.txt
printf 'file=%s\n' *(N.)
printf 'dir=%s\n' *(N/)

Zsh · exit 0

file=a.txt
dir=data

View complete example

BSH-14-004Zsh comparison

Zsh difference: recurse through directories

Code preview

mkdir -p data/raw
touch top.csv data/raw/sample.csv
printf '%s\n' **/*.csv(N)

Zsh · exit 0

data/raw/sample.csv
top.csv

View complete example

BSH-14-005

Bash: recursive globbing

Code preview

mkdir -p data/raw
touch top.csv data/raw/sample.csv
shopt -s globstar nullglob
printf '%s\n' **/*.csv

Bash · exit 0

data/raw/sample.csv
top.csv

View complete example

BSH-14-006

Bash: load lines into an array

Code preview

printf 'alpha\n\nbeta gamma\n' > lines.txt
mapfile -t items < lines.txt
printf 'count=%s\n' "${#items[@]}"
printf '<%s>\n' "${items[@]}"

Bash · exit 0

count=3
<alpha>
<>
<beta gamma>

View complete example

BSH-14-007Zsh comparison

Zsh difference: uppercase a scalar

Code preview

label='Sample A'
printf '%s\n' "${(U)label}" "$label"

Zsh · exit 0

SAMPLE A
Sample A

View complete example

BSH-14-008

Bash: uppercase a scalar

Code preview

label='Sample A'
printf '%s\n' "${label^^}" "$label"

Bash · exit 0

SAMPLE A
Sample A

View complete example

Debugging and controlled failures

6 examples

BSH-15-001

Trace expanded commands in Bash

Code preview

PS4='+ trace: '
set -x
label=sample
printf '%s\n' "$label"
…

Bash · exit 0

sample

Standard error

+ trace: label=sample
+ trace: printf '%s\n' sample
…

View complete example

BSH-15-002Zsh comparison

Zsh difference: Trace expanded commands in Zsh

Code preview

PS4='+ trace: '
set -x
label=sample
printf '%s\n' "$label"
…

Zsh · exit 0

sample

Standard error

+ trace: label=sample 
+ trace: printf '%s\n' sample
…

View complete example

BSH-15-003

A plain failure under errexit

Code preview

set -e
printf 'before\n'
false
printf 'unreachable\n'

Bash · exit 1

before

View complete example

BSH-15-004

A checked failure under errexit

Code preview

set -e
if false; then
  printf 'unreachable\n'
else
…

Bash · exit 0

handled
continues

View complete example

BSH-15-005

Capture status before logging

Code preview

false
exit_code=$?
printf 'command failed\n' >&2
printf 'saved=%s now=%s\n' "$exit_code" "$?"

Bash · exit 0

saved=1 now=0

Standard error

command failed

View complete example

BSH-15-006

Negation changes the observed status

Code preview

if ! false; then
  printf 'negated status=%s\n' "$?"
fi

Bash · exit 0

negated status=0

View complete example

Traps, file descriptors and reusable commands

11 examples

BSH-16-001

Keep a stream on another descriptor

Code preview

exec 3> log.txt
printf 'log entry\n' >&3
printf 'terminal entry\n'
exec 3>&-
…

Bash · exit 0

terminal entry
log entry

View complete example

BSH-16-002

Preserve failure during cleanup

Code preview

cleanup() {
  local exit_code=$?
  printf 'cleanup after status=%s\n' "$exit_code"
  return "$exit_code"
…

Bash · exit 3

cleanup after status=3

View complete example

BSH-16-003

Cancel an exit trap

Code preview

trap 'printf "old handler\n"' EXIT
trap - EXIT
printf 'done\n'

Bash · exit 0

done

View complete example

BSH-16-004

Store a command as an array

Code preview

cmd=(printf '<%s>\n' 'sample A' 'sample B')
"${cmd[@]}"

Bash · exit 0

<sample A>
<sample B>

View complete example

BSH-16-005

Source a small function library

Code preview

cat > helpers.sh <<'LIB'
greet() { printf 'Hello, %s!\n' "$1"; }
LIB
. ./helpers.sh
…

Bash · exit 0

Hello, Ada!

View complete example

BSH-16-006Zsh comparison

Zsh difference: Scope options in a Zsh function

Code preview

collect() {
  emulate -L zsh
  setopt null_glob
  local files=(missing*.csv)
…

Zsh · exit 0

files=0
option restored

View complete example

BSH-16-007

Report a failed command with ERR

Code preview

trap 'status=$?; printf "ERR: status=%s\n" "$status"' ERR
false
printf 'script continues\n'

Bash · exit 0

ERR: status=1
script continues

View complete example

BSH-16-008

A checked failure does not trigger ERR

Code preview

trap 'status=$?; printf "ERR: status=%s\n" "$status"' ERR
if false; then
  printf 'unexpected success\n'
else
…

Bash · exit 0

failure handled

View complete example

BSH-16-009

Keep ERR traps outside a function

Code preview

set +E
trap 'status=$?; printf "ERR: status=%s\n" "$status"' ERR
run_step() {
  false
…

Bash · exit 0

function continues
caller continues

View complete example

BSH-16-010

Inherit ERR traps inside a function

Code preview

set -E
trap 'status=$?; printf "ERR: status=%s\n" "$status"' ERR
run_step() {
  false
…

Bash · exit 0

ERR: status=1
function continues
caller continues

View complete example

BSH-16-011

Combine an ERR report with errexit

Code preview

set -e
trap 'status=$?; printf "ERR: status=%s\n" "$status" >&2' ERR
printf 'before failure\n'
false
…

Bash · exit 1

before failure

Standard error

ERR: status=1

View complete example

Strings, formats and regular expressions

7 examples

BSH-17-001

Take a substring

Code preview

text='sample-2026.csv'
printf '%s\n' "${text:7:4}"

Bash · exit 0

View complete example

BSH-17-002

Count from the end

Code preview

text='sample-2026.csv'
printf '%s\n' "${text: -4}"

Bash · exit 0

.csv

View complete example

BSH-17-003

Format directly into a variable

Code preview

printf -v sample 'sample-%03d' 7
printf '%s\n' "$sample"

Bash · exit 0

sample-007

View complete example

BSH-17-004

Show an argument as reusable shell syntax

Code preview

file='sample A.csv'
printf '%q\n' "$file"

Bash · exit 0

sample\ A.csv

View complete example

BSH-17-005

Match an extended regular expression

Code preview

value='123'
pattern='^[0-9]+$'
if [[ "$value" =~ $pattern ]]; then
  printf 'integer text\n'
…

Bash · exit 0

integer text

View complete example

BSH-17-006

Capture groups from a regex

Code preview

file='sample-042.csv'
pattern='^([a-z]+)-([0-9]+)\.csv$'
if [[ "$file" =~ $pattern ]]; then
  printf 'label=%s number=%s\n' \
…

Bash · exit 0

label=sample number=042

View complete example

BSH-17-007

Quote a regex to match it literally

Code preview

value='123'
pattern='^[0-9]+$'
if [[ "$value" =~ "$pattern" ]]; then
  printf 'literal match\n'
…

Bash · exit 0

no literal match

View complete example

Arithmetic and loop control

6 examples

BSH-18-001

Arithmetic commands return a status

Code preview

(( 2 + 3 ))
printf 'nonzero status=%s\n' "$?"
(( 2 - 2 ))
printf 'zero status=%s\n' "$?"

Bash · exit 0

nonzero status=0
zero status=1

View complete example

BSH-18-002

Postincrement versus preincrement

Code preview

n=0
((n++))
printf 'post: n=%s status=%s\n' "$n" "$?"
n=0
…

Bash · exit 0

post: n=1 status=1
pre: n=1 status=0

View complete example

BSH-18-003

Read a zero-padded decimal integer

Code preview

value=008
printf '%s\n' "$((10#$value + 1))"

Bash · exit 0

View complete example

BSH-18-004

Use an arithmetic for loop

Code preview

for ((i=0; i<3; i++)); do
  printf '%s\n' "$i"
done

Bash · exit 0

0
1
2

View complete example

BSH-18-005

Stop at the first match

Code preview

for value in 3 7 9; do
  if ((value > 5)); then
    printf 'first=%s\n' "$value"
    break
…

Bash · exit 0

first=7

View complete example

BSH-18-006

Compute a decimal result with a utility

Code preview

awk 'BEGIN {printf "%.2f\n", 7 / 2}'

Bash · exit 0

3.50

View complete example

Arrays, indirection and references

8 examples

BSH-19-001

Array indices need not be contiguous

Code preview

items=()
items[2]=alpha
items[5]=beta
printf 'count=%s\n' "${#items[@]}"
…

Bash · exit 0

count=2
index=2
index=5

View complete example

BSH-19-002

Unset one array element

Code preview

items=(alpha beta gamma)
unset 'items[1]'
printf 'index=%s\n' "${!items[@]}"
printf 'value=%s\n' "${items[@]}"

Bash · exit 0

index=0
index=2
value=alpha
value=gamma

View complete example

BSH-19-003

Slice several array elements

Code preview

items=(alpha 'beta gamma' delta epsilon)
printf '<%s>\n' "${items[@]:1:2}"

Bash · exit 0

<beta gamma>
<delta>

View complete example

BSH-19-004

Look up a variable by name

Code preview

label=sample
name=label
printf '%s\n' "${!name}"

Bash · exit 0

sample

View complete example

BSH-19-005

Update through a nameref

Code preview

label=before
declare -n ref=label
ref=after
printf '%s\n' "$label"

Bash · exit 0

after

View complete example

BSH-19-006

Return an array through a function argument

Code preview

make_items() {
  local -n output_ref="$1"
  output_ref=(alpha 'beta gamma')
}
…

Bash · exit 0

<alpha>
<beta gamma>

View complete example

BSH-19-007

List variable names by prefix

Code preview

tour_demo_alpha=12
tour_demo_beta=7
printf '%s\n' "${!tour_demo_@}" | sort

Bash · exit 0

tour_demo_alpha
tour_demo_beta

View complete example

BSH-19-008

Read values through discovered names

Code preview

tour_demo_alpha=12
tour_demo_beta=7
for variable in "${!tour_demo_@}"; do
  printf '%s=%s\n' "$variable" "${!variable}"
…

Bash · exit 0

tour_demo_alpha=12
tour_demo_beta=7

View complete example

Options and controlled file output

6 examples

BSH-20-001

Protect an existing output file

Code preview

printf 'original\n' > report.txt
set -C
if { printf 'replacement\n' > report.txt; } 2>/dev/null; then
  printf 'written\n'
…

Bash · exit 0

overwrite refused
original

View complete example

BSH-20-002

Override noclobber deliberately

Code preview

printf 'original\n' > report.txt
set -C
printf 'replacement\n' >| report.txt
cat report.txt

Bash · exit 0

replacement

View complete example

BSH-20-003

Scope a Bash option with a subshell

Code preview

shopt -u nullglob
(
  shopt -s nullglob
  files=(missing*.csv)
…

Bash · exit 0

inside=0
parent unchanged

View complete example

BSH-20-004

Match case-insensitively

Code preview

shopt -s nocasematch
file='SAMPLE.CSV'
if [[ "$file" == *.csv ]]; then printf 'matched\n'; fi

Bash · exit 0

matched

View complete example

BSH-20-005

Keep the last pipeline builtin in Bash

Code preview

set +m
shopt -s lastpipe
value=before
printf 'after\n' | read -r value
…

Bash · exit 0

after

View complete example

BSH-20-006

Disable filename expansion

Code preview

touch a.txt b.txt
set -f
printf '%s\n' *.txt
set +f
…

Bash · exit 0

*.txt
a.txt
b.txt

View complete example

Reusable script patterns

5 examples

BSH-21-001

Check a dependency before using it

Code preview

if command -v awk >/dev/null 2>&1; then
  printf 'awk available\n'
else
  printf 'awk missing\n' >&2
…

Bash · exit 0

awk available

View complete example

BSH-21-002

Validate an argument count

Code preview

require_one() {
  if (( $# != 1 )); then
    printf 'expected one argument\n' >&2
    return 2
…

Bash · exit 0

input=sample A
validation status=2

Standard error

expected one argument

View complete example

BSH-21-003

Separate data from diagnostic messages

Code preview

produce() {
  printf 'processing sample\n' >&2
  printf '7\n'
}
…

Bash · exit 0

DATA: 7
LOG: processing sample

View complete example

BSH-21-004

A dry-run wrapper preserves arguments

Code preview

run() {
  if [[ "$dry_run" == yes ]]; then
    printf 'would run:'
    printf ' %q' "$@"
…

Bash · exit 0

would run: printf %s\\n sample\ A

View complete example

BSH-21-005

Test a function result explicitly

Code preview

stem() { printf '%s\n' "${1%.csv}"; }
actual=$(stem sample.csv)
if [[ "$actual" != sample ]]; then
  printf 'FAIL: stem\n' >&2
…

Bash · exit 0

PASS: stem

View complete example

Reading the tour

Three ways to see a change

Program

Read a complete script with its own input and an explicit interpreter.

Captured result

Compare standard output, standard error and exit status with the code.

One change

Follow stable identifiers and focused explanations without an accumulating shell session.

Bash is the main interpreter. Amber Zsh difference notes are optional comparisons. They are explicitly labelled; a Bash block requires Bash even when your interactive terminal normally starts Zsh.

Read from the beginning or jump to a stable example ID. Each example includes its complete input and captured result. Copy link preserves the address of the guide you are reading, including its current domain and path.

Bash quick reference

Use these reminders to find a complete program and its captured result. Each example link opens the corresponding section of this tour, including offline. For another compact reference, see the Devhints Bash scripting cheatsheet.

Topic	Reminder	Worked example
Quoting	Keep a scalar together with `"$value"`.	BSH-02-003
Defaults	Use `${value:-fallback}` for an unset or empty value.	BSH-03-001
Path suffixes	Remove a matching suffix with `${file%.*}`.	BSH-03-004
Substrings	Extract a slice with `${text:offset:length}`.	BSH-17-001
Script arguments	Preserve argument boundaries with `"$@"`.	BSH-07-004
Arrays	Keep elements separate with `"${items[@]}"`.	BSH-08-003
Reading lines	Use `IFS= read -r line` to preserve spaces and backslashes.	BSH-07-002
Pipeline failures	Enable `set -o pipefail` to expose an earlier failure.	BSH-06-008
Function status	Test success explicitly with `if task; then`.	BSH-21-005
Process substitution	Read command output through `<(command)`.	BSH-09-005
Regular expressions	Read captures from `BASH_REMATCH` after a successful match.	BSH-17-006
Short options	Parse flags and their values with `getopts`.	BSH-12-002
Here-strings	Feed a string to standard input with `<<< "$text"`.	BSH-05-012
Variable names	Discover names with `"${!tour_demo_@}"`.	BSH-19-007
Error traps	Report an unchecked failure with `trap 'handler' ERR`.	BSH-16-007

The reminders describe Bash. Follow the labelled Zsh comparisons in the worked examples when using Zsh; array indexing and expansion rules can differ.

Read this first

This is a Bash reference, not an exercise book. The main examples use Bash; amber Zsh difference notes are optional comparisons, not required steps. Read each small program together with its actual output. Stable BSH-CC-NNN identifiers survive changes to titles and page order. Each example includes its own input data and runs independently.

The Org source contains each complete program. Read its captured stdout, stderr and exit status beside the code. Bash is the main interpreter; explicitly marked Zsh difference notes show alternative syntax or behavior.

Execution profile: noninteractive Bash --noprofile --norc, or native Zsh -f; LC_ALL=C; fresh temporary HOME. Zsh may still read a system zshenv. Interactive configuration and plugins are outside the test profile. The examples use shell builtins and common Unix utilities. External tool behavior can differ on macOS/BSD; tested versions are recorded in the build report. A Bash block always requires Bash even if your terminal normally starts Zsh.

The build isolates working files but is not a security sandbox. Review code before executing it. In Emacs, load ob-shell (M-x load-library RET ob-shell), then use C-c C-c on a bash or zsh block. Run file-writing blocks in a disposable directory: unlike the supplied builder, plain Babel execution does not create an isolated directory automatically. :results output captures stdout; the custom builder additionally records stderr and exit status.

Interactive companion

These actions require a real terminal and are not part of the executable tests. Tab requests completion; Ctrl-R searches history in common Emacs-style keymaps; Ctrl-A and Ctrl-E move to the start and end of the editing line. Bindings depend on Readline (Bash), ZLE (Zsh), vi/emacs mode and personal configuration.

Use type printf to inspect command resolution. Use bash --version or zsh --version to check the actual interpreter; $SHELL usually describes the login shell, not necessarily the running interpreter. Use bash script.sh or zsh script.zsh explicitly. For an executable script, add #!/usr/bin/env bash or #!/usr/bin/env zsh as its first line, then chmod +x script.sh and run ./script.sh. A shebang is ignored when you explicitly invoke a different interpreter.

Bash interactive configuration commonly belongs in ~/.bashrc; interactive Zsh configuration in ~/.zshrc. Login startup differs. Do not put tour experiments into startup files. Completion setup and prompt themes are outside this scripting tour.

Sources and scope

The explanations were checked against the official Bash Reference Manual (quoting, expansions, arrays, pipelines), the official Zsh manual (expansion, parameters and options) and the Org Babel shell documentation. Output panels are generated by running the supplied code, not copied from those sources.

GNU Bash Reference Manual
Zsh manual
Org Babel shell documentation
Devhints Bash scripting cheatsheet (additional quick reference)

Do not treat set -e as universal error handling: its behavior depends on command context. Prefer explicit validation and deliberate status handling; pipefail helps expose pipeline failures. Never parse ls output to obtain filenames. Arrays and quoted expansions preserve argument boundaries. This expanded tour covers scripting fundamentals and selected advanced patterns. Interactive job control, completion systems and terminal styling remain outside the executable reference.

First commands and formatted output

BSH-01-001

Print a line

printf is a shell builtin. %s inserts a string; \n ends the line. Keep the format string constant.

Bash,one change at a time

All shell examples at a glance

First commands and formatted output

Print a line

One argument, one line

Keep words together

Align columns

Choose decimal precision

Comments and continuation

Variables and quoting

Assign and expand

Single versus double quotes

Bash splits an unquoted scalar

Zsh difference: keeps an unquoted scalar

Zsh difference: Explicit Zsh splitting

Protect a variable boundary

Parameter expansion and arithmetic

A fallback value

Unset versus empty

Assign the fallback

Remove a suffix

Shortest versus longest match

Remove a path prefix

Replace matching text

Integer arithmetic

Files and filename patterns

Create, copy and read

Select a filename suffix

A quoted pattern stays literal

Exactly one character

Brace expansion does not find files

Bash unmatched glob

Zsh difference: unmatched glob

Bash: collect zero matches

Zsh difference: collect zero matches

Streams, redirection and pipes

Write a file

Append instead

Read standard input

Connect two commands

Sort and count repeats

Separate stdout and stderr

Capture both streams

Redirection order matters

A literal here-document

An expanding here-document

Save and continue a stream

Feed a variable through a here-string

An empty here-string still supplies a line

Exit status and decisions

Read the exit status

Run only after success

Recover after failure

Branch on a number

Match a string pattern

Several alternatives with case

Default pipeline status

Enable pipefail

Loops, arguments and functions

Loop over explicit arguments

Read complete lines

Repeat while a condition holds

Preserve positional arguments

Join positional arguments

A function with an argument

Capture a command result

Return a status from a function

Arrays and mappings

Bash starts at index zero

Zsh difference: starts at index one

Preserve array elements

Append an array element

Bash associative array

Zsh difference: associative array

Zsh difference: split and join flags

Zsh difference: path modifiers

Processes, isolation and robust scripts

A subshell isolates assignments

A group shares assignments

Export to a child process

Bash,
one change at a time