Shell Scripting Complete 3: Script Input with Arguments, $@, shift, read and getopts

By Ravindra Bagale, trainer · LinkedIn · Last updated: 25 October 2026

1. An everyday example: ordering at a chai stall

Why do we need this?

At a chai stall you can order in three ways. You can wait for the owner to ask 'kiti?' and answer (read). You can say everything at once, 'two cutting, one without sugar' (arguments). Or you can use the menu codes, 'C2 -S' (options). A good stall understands all three and tells you the menu if you say something wrong.

What is it?

Owner asks = read. Saying it all at once = $1 $2. Count of items = $#. Menu codes = getopts options. Showing the menu = usage message. Wrong order = exit 2.

How to do it (step by step)

2. read: ask the user

Why do we need this?

Some scripts need a value only a person can give, like a ticket number or a yes/no.

What is it?

read name waits for a line and stores it in name. -p 'text' shows a prompt. -r keeps backslashes as typed (always use it). -s hides typing (passwords). -t 10 gives up after 10 seconds. -n 1 reads one key. With several names, words go to each and the rest to the last. With no name, the line goes to $REPLY.

How to do it (step by step)

1. Ask a name.

read -rp 'Your city: ' city; echo "Hello from $city"

Output:

Your city: Nashik
Hello from Nashik

What it means: The typed text went into city.

2. Two values at once.

read -rp 'First Last: ' first last; echo "$last, $first"

Output:

First Last: Sachin Tendulkar
Tendulkar, Sachin

What it means: Words split on spaces.

3. Hidden password.

read -rsp 'DB password: ' pw; echo; echo "got ${#pw} chars"

Output:

DB password: 
got 9 chars

What it means: Nothing was shown while typing.

4. Timeout.

read -t 5 -rp 'Continue? ' ans || echo ' no answer, using default'

Output:

Continue?  no answer, using default

What it means: read returns non-zero on timeout.

3. Yes/no confirmation before danger

Why do we need this?

Deleting, restarting or deploying should ask first, so a slip of the finger does not cause an outage.

What is it?

Read one answer, lower-case it, and continue only on y or yes. Treat everything else (including Enter) as no. Allow a -y option (taught below) so automation can skip the question.

How to do it (step by step)

1. Confirm.

read -rp 'Restart nginx? [y/N] ' a; [[ ${a,,} == y* ]] && echo restarting || echo cancelled

Output:

Restart nginx? [y/N] N
cancelled

What it means: Default is No.

2. One key.

read -n1 -rp 'Press any key to go on...'; echo

Output:

Press any key to go on...

What it means: Waits for a single key.

3. Not a terminal?

[ -t 0 ] && echo interactive || echo 'no tty, skip questions'

Output:

interactive

What it means: In cron [ -t 0 ] is false, so do not ask.

4. Positional arguments: $1, $2, $#, $0

Why do we need this?

Arguments let other people and cron run your script without questions: ./deploy.sh shop prod.

What is it?

Words after the script name become $1, $2 ... ${10} (braces from 10). $# is how many there are. $0 is the script name. Arguments with spaces must be quoted by the caller: ./s.sh "my file". Check $# first and stop with a usage message when something is missing.

How to do it (step by step)

1. See them.

printf '#!/bin/bash\necho "script=$0 count=$# first=$1 second=$2"\n' | tee args.sh && bash args.sh shop prod

Output:

script=args.sh count=2 first=shop second=prod

What it means: Each word got a number.

2. Quoted argument.

bash args.sh "Pune Camp" east

Output:

script=args.sh count=2 first=Pune Camp second=east

What it means: Quotes kept 'Pune Camp' as one.

3. Usage check.

bash -c '[ $# -ge 1 ] || { echo "usage: $0 FILE"; exit 2; }; echo ok' myscript

Output:

usage: myscript FILE

What it means: With bash -c the first word after the code becomes $0.

4. Tenth argument.

set -- a b c d e f g h i j; echo "${10}"

Output:

j

What it means: set -- sets the arguments; ${10} needs braces.

5. "$@" vs "$*" and passing arguments on

Why do we need this?

Wrappers and loops over arguments break on spaces unless you use the right form.

What is it?

"$@" expands to every argument as a separate, quoted word. It is what you want 99% of the time. "$*" joins all arguments into one string with a space (the first char of IFS). Unquoted $@ and $* split on spaces again, so avoid them. To pass all arguments to another command: other_cmd "$@".

How to do it (step by step)

1. Loop safely.

set -- 'a b' c; for x in "$@"; do echo "[$x]"; done

Output:

[a b]
[c]

What it means: Each argument kept whole.

2. Joined.

set -- 'a b' c; echo "[$*]"

Output:

[a b c]

What it means: One string.

3. A wrapper.

printf '#!/bin/bash\necho "[wrapper] running ls $*"\nexec ls -l "$@"\n' | tee myls.sh && bash myls.sh /etc/hosts

Output:

[wrapper] running ls /etc/hosts
-rw-r--r-- 1 root root 220 Oct 1 /etc/hosts

What it means: $* for the message, "$@" for the command.

6. shift: walk through arguments

Why do we need this?

When the first arguments are special (like a command name) you want to remove them and treat the rest as a list.

What is it?

shift drops $1 and moves every argument one place left, so $2 becomes $1 and $# goes down by one. shift 2 drops two. A common loop is while [ $# -gt 0 ]; do ...; shift; done. Use it for simple long options like --dry-run that getopts cannot handle.

How to do it (step by step)

1. Basic.

set -- deploy web1 web2; cmd=$1; shift; echo "$cmd on: $*"

Output:

deploy on: web1 web2

What it means: The command is removed from the list.

2. Loop.

set -- x y z; while [ $# -gt 0 ]; do echo "item $1 (left $#)"; shift; done

Output:

item x (left 3)
item y (left 2)
item z (left 1)

What it means: Each shift moves to the next.

3. Long options by hand.

set -- --dry-run --env stage app; while [ $# -gt 0 ]; do case $1 in --dry-run) dry=1;; --env) env=$2; shift;; *) break;; esac; shift; done; echo "dry=$dry env=$env rest=$*"

Output:

dry=1 env=stage rest=app

What it means: --env takes a value, so it shifts twice.

7. getopts: proper options like -v and -d DIR

Why do we need this?

Users expect tools to accept -h, -v, -n 5 in any order and combined like -vn 5. getopts does this for you.

What is it?

while getopts 'hvd:' opt; do case $opt in ... esac; done. Each letter is an option; a colon after it (d:) means it needs a value, found in $OPTARG. A leading colon (':hvd:') lets you handle errors yourself: \? for an unknown option and : for a missing value. After the loop, shift $((OPTIND-1)) removes the options so $1 is the first normal argument. getopts only handles short options.

How to do it (step by step)

1. A script.

cat backup.sh

Output:

#!/bin/bash
verbose=0; dest=/backup
while getopts ':hvd:' opt; do
  case $opt in
    h) echo "usage: $0 [-v] [-d DIR] SRC..."; exit 0;;
    v) verbose=1;;
    d) dest=$OPTARG;;
    :) echo "-$OPTARG needs a value"; exit 2;;
    \?) echo "unknown -$OPTARG"; exit 2;;
  esac
done
shift $((OPTIND-1))
echo "verbose=$verbose dest=$dest sources=$*"

What it means: h and v are flags; d needs a value.

2. Use it.

./backup.sh -v -d /mnt/usb /etc /home

Output:

verbose=1 dest=/mnt/usb sources=/etc /home

What it means: After shift only the folders remain.

3. Combined flags.

./backup.sh -vd /srv/bk /var/www

Output:

verbose=1 dest=/srv/bk sources=/var/www

What it means: -vd /srv/bk is the same as -v -d /srv/bk.

4. Errors.

./backup.sh -x; ./backup.sh -d

Output:

unknown -x
-d needs a value

What it means: Clear messages and exit 2.

8. Usage message and input checks

Why do we need this?

Most bad runs come from wrong input. Check it at the top and explain how to use the script.

What is it?

Write a usage() function that prints the syntax to stderr (>&2) and exits 2. Call it when $# is wrong or -h is given. Check that numbers are numbers ([[ $n =~ ^[0-9]+$ ]]), that files exist ([ -f ]), and that folders are writable ([ -w ]). The if chapter explains these tests.

How to do it (step by step)

1. Usage function.

usage(){ echo "usage: cleanup.sh DAYS DIR" >&2; exit 2; }; type usage | head -1

Output:

usage is a function

What it means: It prints to stderr and exits.

2. Number check.

n=abc; [[ $n =~ ^[0-9]+$ ]] && echo number || echo 'not a number'

Output:

not a number

What it means: Regex keeps only digits.

3. File check.

f=/etc/nope.conf; [ -f "$f" ] || echo "missing $f" >&2

Output:

missing /etc/nope.conf

What it means: Stop before doing anything.

9. Reading from stdin, pipes and files

Why do we need this?

Good tools work in pipes: cat list.txt | ./check.sh. Your script can read lines the same way.

What is it?

If no file is given, read from standard input. while IFS= read -r line; do ...; done reads one line at a time (chapter 5 explains IFS). < file sends a file in. A here-string <<< "text" sends one string. A here-document <

How to do it (step by step)

1. Pipe in.

printf 'web1\nweb2\n' | while IFS= read -r h; do echo "checking $h"; done

Output:

checking web1
checking web2

What it means: Each line in turn.

2. Here-string.

read -r a b <<< 'Pune 411001'; echo "$b $a"

Output:

411001 Pune

What it means: One string into read.

3. Here-document.

cat <<EOF
Host: $(hostname)
User: $USER
EOF

Output:

Host: web01
User: asha

What it means: Variables expanded inside.

4. File or stdin.

in=${1:-/dev/stdin}; wc -l < "$in"

Output:

3

What it means: /dev/stdin is used when no file is given.

10. Real examples from many industries

Why do we need this?

The same Linux skill shows up in every kind of company. Seeing it in many places helps you remember it.

What is it?

Each row is a made-up team. It shows who uses this and how.

How to do it (step by step)

11. Common errors and how to fix them

Why do we need this?

Everyone hits these errors. Knowing the cause saves hours.

What is it?

Read the exact message first. Then match it to a row below.

How to do it (step by step)

12. Troubleshooting step by step

Why do we need this?

Print what the script really received.

What is it?

Go top to bottom. Stop at the first step that shows the problem.

How to do it (step by step)

1. Count.

echo "count=$#"

2. Each argument.

printf '[%s]\n' "$@"

3. Option state.

echo "OPTIND=$OPTIND OPTARG=$OPTARG"

4. Terminal?

[ -t 0 ] && echo tty

5. Trace parsing.

bash -x s.sh -v -d /tmp x

6. Hidden characters in input.

printf '%q\n' "$1"

13. Lab 1: A greeting script with read and arguments

Why do we need this?

Write greet.sh that uses $1 if given, otherwise asks with read, and checks the input.

What is it?

A full hands-on lab. Run every step on a test Linux machine (an EC2 instance, a VM, or WSL).

How to do it (step by step)

1. Folder.

mkdir -p ~/lab39 && cd ~/lab39

2. Write.

printf '#!/bin/bash\nname=${1:-}\nif [ -z "$name" ]; then read -rp "Name: " name; fi\n[ -n "$name" ] || { echo "name required" >&2; exit 2; }\necho "Namaskar, $name!"\n' | tee greet.sh && chmod +x greet.sh

3. With an argument.

./greet.sh Meera

Output:

Namaskar, Meera!

4. Without.

./greet.sh

Output:

Name: Raj
Namaskar, Raj!

5. Empty input.

./greet.sh <<< ''; echo $?

Output:

name required
2

6. From a pipe.

echo Sara | ./greet.sh

Output:

Namaskar, Sara!

14. Lab 2: A real getopts tool

Why do we need this?

Build findbig.sh with -n COUNT, -d DIR and -h, which lists the largest files.

What is it?

A full hands-on lab. Run every step on a test Linux machine (an EC2 instance, a VM, or WSL).

How to do it (step by step)

1. Write the parser.

printf '#!/bin/bash\nn=5; d=.\nwhile getopts ":hn:d:" o; do case $o in h) echo "usage: $0 [-n N] [-d DIR]"; exit 0;; n) n=$OPTARG;; d) d=$OPTARG;; :) echo "-$OPTARG needs value" >&2; exit 2;; \\?) echo "bad -$OPTARG" >&2; exit 2;; esac; done\nshift $((OPTIND-1))\n[[ $n =~ ^[0-9]+$ ]] || { echo "N must be a number" >&2; exit 2; }\ndu -ah "$d" 2>/dev/null | sort -rh | head -n "$n"\n' | tee findbig.sh && chmod +x findbig.sh

2. Help.

./findbig.sh -h

Output:

usage: ./findbig.sh [-n N] [-d DIR]

3. Default.

./findbig.sh -d /var/log | head -2

Output:

1.2G /var/log
800M /var/log/journal

4. Three in /etc.

./findbig.sh -n 3 -d /etc

Output:

6.1M /etc
3.0M /etc/selinux
1.1M /etc/ssl

5. Bad number.

./findbig.sh -n many; echo $?

Output:

N must be a number
2

6. Missing value.

./findbig.sh -d

Output:

-d needs value

15. Frequently asked questions

16. Interview questions and answers

Beginner level

Mid level level

Senior level

17. Related chapters

• Linux Ops Refresh for DevOps
• Bash Scripting for Automation
• Linux grep and find Commands with Examples
• How to Set Up Passwordless SSH Between Linux Servers

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