Bash Cheatsheet - Shell Scripting Command Reference

Essential Bash scripting syntax on one page. Variables, loops, functions, and string operations — reference directly when writing shell scripts.

SysOps·43 commands·Last updated 2026-07-21

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Variables 8

NAME="value"

Define variable (no spaces around =)

echo $NAME

Read variable

echo ${NAME}

Read variable (recommended, avoids ambiguity)

readonly NAME="value"

Define readonly variable

unset NAME

Delete variable

${VAR:-default}

Use default value if variable is empty

${VAR:=default}

Assign and use default if variable is empty

${#VAR}

Get string length

Conditionals 7

if [ condition ]; then ... fi

if statement

if [ -f file ]; then ... fi

Check if file exists

if [ $a -eq $b ]; then ... fi

Numeric comparison (-eq -ne -gt -lt)

if [ "$str" = "value" ]; then ... fi

String comparison (= !=)

if [[ $str =~ regex ]]; then ... fi

Regex match (double brackets)

[ -d dir ] && echo "exists"

Short-circuit evaluation

case $var in pattern1) ... ;; pattern2) ... ;; esac

case statement

Loops 6

for i in 1 2 3; do echo $i; done

for loop over a list

for ((i=0; i<10; i++)); do ... done

C-style for loop

while [ condition ]; do ... done

while loop

until [ condition ]; do ... done

until loop (executes while condition is false)

break / continue

Break out of loop / skip iteration

select var in list; do ... done

Interactive selection menu

Functions 7

function name() { ... }

Define a function

name() { ... }

Define function (shorthand)

name arg1 arg2

Call a function

$1 $2 $@

Positional parameters / all parameters

$#

Number of parameters

return 0

Return value (0 means success)

local var="value"

Local variable

String Operations 7

${VAR:offset:length}

Substring extraction

${VAR#pattern}

Remove shortest matching prefix

${VAR##pattern}

Remove longest matching prefix

${VAR%pattern}

Remove shortest matching suffix

${VAR%%pattern}

Remove longest matching suffix

${VAR/pattern/replacement}

Replace first match

${VAR//pattern/replacement}

Replace all matches

File Tests 8

[ -f file ]

File exists and is a regular file

[ -d dir ]

Directory exists

[ -e path ]

Path exists

[ -r file ]

File is readable

[ -w file ]

File is writable

[ -x file ]

File is executable

[ -s file ]

File size is greater than 0

[ file1 -nt file2 ]

file1 is newer than file2

Tips

No spaces around = in variable assignment, or it will be interpreted as a command.
Always quote variables ("$VAR") to avoid word splitting and special character issues.
[ ] is syntactic sugar for the test command; [[ ]] is a Bash extension with more features like regex matching.

Official References

Commands are compiled from the official docs below. Click to verify the latest usage.

Linux man-pages

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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