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Dash

July 19, 2025

🧘‍♀️ Flow State and Fast Shells: Understanding Dash for Beginners

In the yoga world, there’s this concept called “drishti”—a focused gaze. It’s not just about where you look during a pose, it’s about narrowing your attention to what truly matters, shedding the unnecessary to move with clarity and purpose. Think of a seasoned yogi in a crowded class: the room could be full of distractions—mirrors, other people wobbling in Tree Pose—but they stay laser-focused, breath aligned, body balanced, movement efficient.

This is Dash. In the chaotic world of scripting and system processes, Dash is that yogi. Minimal. Fast. Focused. It doesn’t care about fluff—it’s built to do one thing: run shell scripts quickly and efficiently.

🖥️ So… What is Dash, Technically?

Dash stands for Debian Almquist Shell. It’s a lightweight, POSIX-compliant shell used primarily for scripting, not for interactive shell sessions like you might do in your terminal.

If you’ve ever written a script and started it with:

#!/bin/sh

There's a good chance it’s actually being run by Dash on many Linux systems (especially Debian-based ones like Ubuntu). That’s because /bin/sh on those systems often points to Dash—not Bash.

Why? Because Dash is fast. It's streamlined to execute shell scripts more quickly than its bulkier siblings, which matters a lot when your system is booting or running hundreds of tiny scripts behind the scenes.

🆚 Dash vs Bash vs SH: What’s the Difference?

Let’s roll out the mat and get into the differences in style and purpose, yogi-style:

🧘 Dash: The Minimalist Yogi

🥋 Bash: The Vinyasa Flow Master

👣 SH: The Ancestral Guide

💡 Why Should a Beginner Care About Dash?

Let’s say you’re just getting into scripting. You might not notice the milliseconds Dash saves at first. But imagine you're writing a script that runs every time your system boots, or every few minutes via cron. Multiply that over time, across hundreds of scripts—that’s impact.

Also, learning to write scripts that work in Dash (i.e., POSIX-compliant scripts) is a great habit. It forces you to keep things simple, portable, and robust. It’s like learning to hold your Warrior II pose with precision before trying to fly into a handstand.

🧘‍♂️ Final Pose: Keep It Light

In yoga, the most advanced practitioners often return to the basics—mastering the breath, the stillness, the form. Likewise, in scripting, sometimes the most efficient solution is the simplest one. Dash embodies that philosophy.

So if you’re just starting out with shell scripting, give Dash a try. Strip things back. Focus your gaze. Feel the breath of your system moving lighter and faster.

Namaste—and happy scripting with the examples below. ✨

Examples

Below is a top 100 list of common Dash shell scripting lines/blocks, tailored to beginners, but written with clarity and real-world relevance. These are all POSIX-compliant, meaning they’ll work in Dash (which doesn't support Bash-only features like arrays or syntax).

🧾 Top 30 Common Lines of Code in Dash Shell Scripts

🔧 1. Shebang Line (Start of Script)

#!/bin/dash

📂 2. Defining a Variable

NAME="Alice"

🖨️ 3. Printing Text

echo "Hello, $NAME"

🧪 4. Basic If Statement

if [ "$NAME" = "Alice" ]; then
  echo "Welcome, Alice!"
fi

🔁 5. While Loop

i=1
while [ "$i" -le 5 ]; do
  echo "Loop $i"
  i=$((i + 1))
done

🔃 6. For Loop

for FILE in *.txt; do
  echo "Found file: $FILE"
done

🧭 7. Check If File Exists

if [ -f "config.cfg" ]; then
  echo "Config file exists."
fi

📁 8. Check If Directory Exists

if [ -d "/etc" ]; then
  echo "/etc exists."
fi

🆓 9. Check If File is Executable

if [ -x "script.sh" ]; then
  echo "Script is executable."
fi

🖥️ 10. Running a Command

uptime

💣 11. Error Exit

echo "Something failed!" >&2
exit 1

📜 12. Reading User Input

echo "Enter your name:"
read USERNAME
echo "Hello, $USERNAME"

📦 13. Command Substitution

DATE=$(date)
echo "Today is $DATE"

💬 14. Quoting Variables Safely

echo "User input: "$USER_INPUT""

🧹 15. Deleting a File

rm -f temp.txt

🧍 16. Function Definition

greet() {
  echo "Hello, $1"
}
greet "Dash"

⚖️ 17. Else Statement

if [ "$USER" = "root" ]; then
  echo "Running as root"
else
  echo "Not root"
fi

🔄 18. Elif Statement

if [ "$x" -gt 10 ]; then
  echo "Greater than 10"
elif [ "$x" -eq 10 ]; then
  echo "Exactly 10"
else
  echo "Less than 10"
fi

📶 19. Checking Exit Status

some_command
if [ $? -eq 0 ]; then
  echo "Success"
else
  echo "Failed"
fi

📤 20. Redirect Output to File

echo "Log entry" >> logfile.txt

🧾 21. Read File Line by Line

while IFS= read -r line; do
  echo "Line: $line"
done < file.txt

⛔ 22. Test String Empty

if [ -z "$VAR" ]; then
  echo "VAR is empty"
fi

✅ 23. Test String Not Empty

if [ -n "$VAR" ]; then
  echo "VAR is not empty"
fi

🕳️ 24. Redirect stderr to File

command 2> errors.txt

📛 25. Redirect stdout and stderr

command > output.txt 2>&1

🧭 26. Check Command Exists

if command -v curl >/dev/null 2>&1; then
  echo "curl is installed"
fi

🗜️ 27. String Comparison

if [ "$a" = "$b" ]; then
  echo "Equal"
fi

📊 28. Numeric Comparison

if [ "$a" -lt 100 ]; then
  echo "Less than 100"
fi

🚥 29. Using Case Statement

case "$1" in
  start) echo "Starting...";;
  stop) echo "Stopping...";;
  *) echo "Usage: $0 {start|stop}";;
esac

🚀 30. Run Script with Arguments

echo "First arg: $1"
echo "All args: $@"

🔄 31. Loop Through Arguments

for ARG in "$@"; do
  echo "Arg: $ARG"
done

📉 32. Decrement a Number

i=5
i=$((i - 1))

🧮 33. Basic Arithmetic

sum=$((3 + 4))
echo "Sum: $sum"

🔗 34. Combining Commands with &&

mkdir backup && echo "Directory created"

⛓️ 35. Combining Commands with ||

mkdir backup || echo "Failed to create directory"

🧩 36. Checking Multiple Conditions

if [ "$x" -gt 5 ] && [ "$x" -lt 10 ]; then
  echo "x is between 6 and 9"
fi

🔃 37. Infinite Loop

while :; do
  echo "Running forever"
  sleep 1
done

📜 38. Here Document (multi-line string)

cat <<EOF
Line 1
Line 2
EOF

🚫 39. Check If Command Fails

if ! grep "word" file.txt; then
  echo "Word not found"
fi

🧠 40. Use set -e to Exit on Error

set -e
# Any command failing here will exit the script

🔒 41. Use set -u to Error on Unset Variables

set -u
echo "$UNSET_VAR"  # Will cause error if UNSET_VAR is undefined

🌐 42. Ping a Host

ping -c 1 google.com >/dev/null 2>&1 && echo "Online"

⏳ 43. Sleep for Seconds

sleep 5

🧱 44. Check File is Non-Empty

if [ -s "file.txt" ]; then
  echo "File has content"
fi

🏃 45. Execute Script with Exec

exec ./child_script.sh

📂 46. Get Script Directory

DIR=$(cd "$(dirname "$0")" && pwd)
echo "Script is in $DIR"

🎯 47. Check If Directory Is Writable

if [ -w "/tmp" ]; then
  echo "Writable"
fi

🔧 48. Check If Variable Is a Number

case $VAR in
  ''|*[!0-9]*) echo "Not a number" ;;
  *) echo "It’s a number" ;;
esac

🧹 49. Remove All .log Files

rm -f *.log

🗓️ 50. Get Today’s Date

TODAY=$(date +%F)
echo "Today is $TODAY"

📈 51. Compare Two Files

if cmp -s file1.txt file2.txt; then
  echo "Files are the same"
fi

📖 52. Count Lines in File

LINES=$(wc -l < file.txt)
echo "Lines: $LINES"

🕰️ 53. Time a Command

START=$(date +%s)
your_command
END=$(date +%s)
echo "Took $((END - START)) seconds"

🔄 54. Loop with Step (increment by 2)

i=0
while [ "$i" -le 10 ]; do
  echo "$i"
  i=$((i + 2))
done

📍 55. Print Each Character of a String

STR="hello"
i=0
while [ "$i" -lt "${#STR}" ]; do
  echo "${STR:$i:1}"
  i=$((i + 1))
done

⚠️ Not POSIX — string slicing like ${STR:$i:1} isn't valid in Dash. A workaround would be needed. So this one should be skipped or rewritten using cut.

🧪 55. (Fixed) Loop Over Each Char with POSIX fold

echo "$STR" | fold -w1 | while read -r ch; do
  echo "$ch"
done

🏷️ 56. Truncate a File

> file.txt

🔚 57. End Script Early

exit 0

💾 58. Redirect to New File (Overwrite)

echo "New content" > file.txt

🧱 59. Create Directory If Not Exists

[ -d "logs" ] || mkdir logs

🗃️ 60. Get Number of Arguments

echo "You passed $# arguments."

You got it. Here's the next 40 Dash-compatible scripting lines/blocks, taking us from 61 to 100, with practical, real-world use still in focus — no Bash-only features, strictly POSIX/Dash-safe.

🧾 Dash Shell Scripting: Snippets 61–100

📊 61. Loop Over Numbers with seq

for i in $(seq 1 5); do
  echo "Number: $i"
done

📎 62. Append to Variable

STR="hello"
STR="${STR} world"
echo "$STR"

🧩 63. Default Value If Variable Is Empty

echo "${NAME:-Guest}"

🗂️ 64. Create Nested Directories

mkdir -p parent/child/grandchild

🧼 65. Trim Whitespace Using sed

TRIMMED=$(echo "$INPUT" | sed 's/^:space:*//;s/:space:*$//')

📁 66. List All Files in Directory

for f in *; do
  echo "File: $f"
done

🏃‍♂️ 67. Run Command in Background

long_running_task &

⏳ 68. Wait for Background Job

long_running_task &
PID=$!
wait "$PID"
echo "Done"

🛑 69. Trap Script Exit

trap 'echo "Exiting..."; cleanup' EXIT

🪤 70. Trap Ctrl+C

trap 'echo "Interrupted!"; exit 1' INT

🧾 71. Check File Contains Text

if grep -q "needle" haystack.txt; then
  echo "Found it!"
fi

🗄️ 72. Copy File

cp source.txt backup.txt

✂️ 73. Move (or Rename) File

mv file.txt archive.txt

🗑️ 74. Delete Empty Directories

find . -type d -empty -delete

🧮 75. Round Down Division

echo $((7 / 2))  # Outputs 3

🧑‍🤝‍🧑 76. Get Current User

USER=$(whoami)

🧠 77. Check if Variable Is Set

if [ "${VAR+set}" = "set" ]; then
  echo "VAR is set"
fi

🕳️ 78. Redirect Only Stdout (Not Stderr)

command > out.txt

🛠️ 79. Create an Empty File

touch newfile.txt

🔗 80. Create a Symbolic Link

ln -s /path/to/original linkname

🔐 81. Check If Port is Open (TCP)

if nc -z 127.0.0.1 80; then
  echo "Port open"
fi

🧬 82. Replace Text in File (in-place)

sed -i 's/old/new/g' file.txt

⚠️ Use sed -i '' on macOS (not POSIX, but still widely used).

🖼️ 83. Get File Extension

EXT="${FILE##*.}"

🧾 84. Read Key Without Enter

stty -echo -icanon time 0 min 1
read -r key
stty sane

📚 85. Print Script Usage

if [ $# -eq 0 ]; then
  echo "Usage: $0 <arg>"
  exit 1
fi

🔐 86. Check If User Is Root

if [ "$(id -u)" -eq 0 ]; then
  echo "You are root"
fi

📦 87. Find Files by Name

find . -name "*.log"

🧹 88. Delete Files Older Than 7 Days

find . -type f -mtime +7 -exec rm {} ;

📎 89. Export a Variable to Subprocesses

export API_KEY="abc123"

📋 90. Read First Line of File

read -r FIRST < file.txt

🧮 91. Incrementing a Variable Inside a Loop

i=0
while [ "$i" -lt 3 ]; do
  echo "$i"
  i=$((i + 1))
done

📤 92. List Running Processes

ps -ef

🗳️ 93. Choose Option With Case

case "$1" in
  yes) echo "You said yes" ;;
  no)  echo "You said no" ;;
  *)   echo "Unknown input" ;;
esac

🔐 94. Check for Environment Variable

if [ -n "$HOME" ]; then
  echo "HOME is set"
fi

📦 95. Compress Files With tar

tar czf archive.tar.gz folder/

📂 96. Unpack a .tar.gz

tar xzf archive.tar.gz

🧪 97. Check Number of Args

if [ "$#" -ne 2 ]; then
  echo "Provide 2 arguments."
  exit 1
fi

📥 98. Download a File with wget

wget https://example.com/file.txt

🔎 99. Search Logs for Keyword

grep -i "error" logfile.txt

📟 100. Get Script Name

SCRIPT_NAME=$(basename "$0")

📘 Bonus Tip: Always Test in a Dash Shell

Want to make sure your script is truly Dash-compatible?

Run it like this explicitly:

dash your_script.sh