bashANYvariablesassignment
bash
name='Jonathan'Do not put spaces around = in shell assignment.
Bash Variables, Quoting, and Expansion
Bash variables, parameter expansion, quoting rules, command substitution, arithmetic, and shell expansion patterns.
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Variables
Assign, export, inspect, and unset variables.
bashANYvariablesquotes
bash
echo "$name"Double quotes preserve spaces and most characters.
bashANYexportenv
bash
export APP_ENV=productionNeeded when subprocesses should receive the value.
bashANYunsetvariables
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unset nameUseful for cleanup and testing default expansion behavior.
bashANYparameter-expansiondefaults
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echo "${PORT:-3000}"One of the most common parameter expansion patterns.
bashANYparameter-expansiondefaults
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echo "${PORT:=3000}"Be careful because this mutates the variable.
bashANYparameter-expansionvalidation
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echo "${DATABASE_URL:?DATABASE_URL is required}"Great for defensive scripts and deployment checks.
bashANYparameter-expansionconditional
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echo "${DEBUG:+enabled}"Good for optional flags and output labels.
Quoting
Single quotes, double quotes, escaping, and ANSI-C quoting.
bashANYquotesliteral
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echo 'Path is $HOME'Use when you need literal shell characters.
bashANYquotesexpansion
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echo "Path is $HOME"Usually the safest choice around variable expansions.
bashANYquotesescape
bash
echo "A quote: \""Needed when embedding quotes in strings.
bashANYquotesansi-c
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printf '%s
' $'line1
line2'Bash supports $'...' expansion for escaped literals.
bashANYquotesliteral
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echo '\$HOME'Handy when writing examples or templates.
Parameter and Command Expansion
Substring, replacement, command substitution, and arithmetic.
bashANYsubstitutioncommands
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today=$(date +%F)Prefer $(...) over backticks for clarity and nesting.
bashANYarithmeticexpansion
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echo $((2 + 3 * 4))Useful for counters, lengths, and simple math.
bashANYlengthstrings
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echo "${#name}"Works for strings and arrays.
bashANYsubstringstrings
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echo "${name:0:4}"Offsets are zero-based.
bashANYreplacestrings
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echo "${file/.txt/.bak}"Useful for filename transforms.
bashANYreplacestrings
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echo "${path//\//:}"The doubled slash means global replacement.
bashANYprefixsuffixpatterns
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echo "${path#*/}"Handy for path processing.
bashANYprefixsuffixpatterns
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echo "${file%%.*}"Useful for basename-like operations and extensions.
Globbing and Brace Expansion
Filename matching and brace generation.
bashANYglobfiles
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printf '%s
' *.txtGlobs are expanded by the shell before command execution.
bashANYbrace-expansiongeneration
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printf '%s
' file-{a,b,c}.txtBrace expansion happens before pathname expansion.
bashANYbrace-expansionsequence
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printf '%s
' {1..5}Great for loops and quick test data.
bashANYglobshopt
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shopt -s nullglobSafer than leaving a literal pattern in loops.
bashANYglobshopt
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shopt -s dotglobUseful for file moves and maintenance tasks.
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Comprehensive Bash commands, shell syntax, quoting, variables, redirection, pipelines, and day-to-day scripting patterns.
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